From b389f4d3aa38be375589b327696ab763904b8da5 Mon Sep 17 00:00:00 2001 From: nicksxs Date: Sun, 11 Oct 2020 23:24:36 +0800 Subject: [PATCH] Site updated: 2020-10-11 23:24:34 --- 2014/12/23/my-new-post/index.html | 8 +- 2014/12/24/MFC 模态对话框/index.html | 8 +- 2014/12/30/Clone-Graph-Part-I/index.html | 10 +- 2015/01/04/Path-Sum/index.html | 14 +- 2015/01/14/Two-Sum/index.html | 14 +- .../index.html | 8 +- 2015/03/11/Number-Of-1-Bits/index.html | 14 +- 2015/03/11/Reverse-Bits/index.html | 14 +- 2015/03/13/Reverse-Integer/index.html | 14 +- 2015/04/14/Add-Two-Number/index.html | 14 +- 2015/04/15/Leetcode-No-3/index.html | 14 +- 2015/06/22/invert-binary-tree/index.html | 14 +- 2016/07/13/swoole-websocket-test/index.html | 8 +- 2016/08/14/34-Search-for-a-Range/index.html | 18 +- 2016/08/14/docker-mysql-cluster/index.html | 14 +- 2016/09/29/binary-watch/index.html | 14 +- .../minimum-size-subarray-sum-209/index.html | 14 +- 2016/10/12/summary-ranges-228/index.html | 14 +- .../index.html | 8 +- 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          在老丈人家的小工记三
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        • 这周末我又在老丈人家打了天小工
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          周末我在老丈人家打了天小工
        • -
          在老丈人家的小工记四
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        • 我是如何走上跑步这条不归路的
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          又 roll 到了一个以前做过的题，不过现在用 Java 也来写一下，是 easy 级别的，所以就简单说下

          +

          简要介绍

          You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

          +

          You may assume the two numbers do not contain any leading zero, except the number 0 itself.
          就是给了两个链表，用来表示两个非负的整数，在链表中倒序放着，每个节点包含一位的数字，把他们加起来以后也按照原来的链表结构输出

          +

          样例

          example 1

          1
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          Input: l1 = [2,4,3], l2 = [5,6,4]
          Output: [7,0,8]
          Explanation: 342 + 465 = 807.
          + +

          example 2

          1
          2
          Input: l1 = [0], l2 = [0]
          Output: [0]
          + +

          example 3

          1
          2
          Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
          Output: [8,9,9,9,0,0,0,1]
          + +

          题解

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          public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
                  ListNode root = new ListNode();
                  if (l1 == null && l2 == null) {
                      return root;
                  }
                  ListNode tail = root;
                  int entered = 0;
                  // 这个条件加了 entered，就是还有进位的数
                  while (l1 != null || l2 != null || entered != 0) {
                      int temp = entered;
                      if (l1 != null) {
                          temp += l1.val;
                          l1 = l1.next;
                      }
                      if (l2 != null) {
                          temp += l2.val;
                          l2 = l2.next;
                      }
                      entered = (temp - temp % 10) / 10;
                      tail.val = temp % 10;
                      // 循环内部的控制是为了排除最后的空节点
                      if (l1 != null || l2 != null || entered != 0) {
                          tail.next = new ListNode();
                          tail = tail.next;
                      }
                  }
          //        tail = null;
                  return root;
              }
          +

          这里唯二需要注意的就是两个点，一个是循环条件需要包含进位值还存在的情况，还有一个是最后一个节点，如果是空的了，就不要在 new 一个出来了，写的比较挫

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          - Nice! 70 posts in total. Keep on posting. + Nice! 71 posts in total. Keep on posting.
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          - Nice! 70 posts in total. Keep on posting. + Nice! 71 posts in total. Keep on posting.
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          - Nice! 70 posts in total. Keep on posting. + Nice! 71 posts in total. Keep on posting.
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          在工作中碰到的一点C++指针上的一点小问题

          +

          在C++中，应该是从C语言就开始了，除了void型指针之外都是需要有分配对应的内存才可以使用，同时malloc与free成对使用，new与delete成对使用，否则造成内存泄漏。

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          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + + In + + + + , + + + + , + + + + , + + + + , + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          这个问题也是面试中常被问到的，就抽空来了解下这个，跳过一大段前面初始化的逻辑，
          对于一条select * from t1 where id = #{id}这样的 sql，在初始化扫描 mapper 的xml文件的时候会根据是否是 dynamic 来判断生成 DynamicSqlSource 还是 RawSqlSource，这里它是一条 RawSqlSource，
          在这里做了替换，将#{}替换成了?

          前面说的是否 dynamic 就是在这里进行判断

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          // org.apache.ibatis.scripting.xmltags.XMLScriptBuilder#parseScriptNode
          public SqlSource parseScriptNode() {
              MixedSqlNode rootSqlNode = parseDynamicTags(context);
              SqlSource sqlSource;
              if (isDynamic) {
                sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
              } else {
                sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
              }
              return sqlSource;
            }
          // org.apache.ibatis.scripting.xmltags.XMLScriptBuilder#parseDynamicTags
          protected MixedSqlNode parseDynamicTags(XNode node) {
              List<SqlNode> contents = new ArrayList<>();
              NodeList children = node.getNode().getChildNodes();
              for (int i = 0; i < children.getLength(); i++) {
                XNode child = node.newXNode(children.item(i));
                if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {
                  String data = child.getStringBody("");
                  TextSqlNode textSqlNode = new TextSqlNode(data);
                  if (textSqlNode.isDynamic()) {
                    contents.add(textSqlNode);
                    isDynamic = true;
                  } else {
                    contents.add(new StaticTextSqlNode(data));
                  }
                } else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) { // issue #628
                  String nodeName = child.getNode().getNodeName();
                  NodeHandler handler = nodeHandlerMap.get(nodeName);
                  if (handler == null) {
                    throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
                  }
                  handler.handleNode(child, contents);
                  isDynamic = true;
                }
              }
              return new MixedSqlNode(contents);
            }
          // org.apache.ibatis.scripting.xmltags.TextSqlNode#isDynamic
            public boolean isDynamic() {
              DynamicCheckerTokenParser checker = new DynamicCheckerTokenParser();
              GenericTokenParser parser = createParser(checker);
              parser.parse(text);
              return checker.isDynamic();
            }
              private GenericTokenParser createParser(TokenHandler handler) {
              return new GenericTokenParser("${", "}", handler);
            }
          +

          可以看到其中一个条件就是是否有${}这种占位符，假如说上面的 sql 换成 ${}，那么可以看到它会在这里创建一个 dynamicSqlSource,

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          // org.apache.ibatis.scripting.xmltags.DynamicSqlSource
          public class DynamicSqlSource implements SqlSource {

            private final Configuration configuration;
            private final SqlNode rootSqlNode;

            public DynamicSqlSource(Configuration configuration, SqlNode rootSqlNode) {
              this.configuration = configuration;
              this.rootSqlNode = rootSqlNode;
            }

            @Override
            public BoundSql getBoundSql(Object parameterObject) {
              DynamicContext context = new DynamicContext(configuration, parameterObject);
              rootSqlNode.apply(context);
              SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
              Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
              SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
              BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
              context.getBindings().forEach(boundSql::setAdditionalParameter);
              return boundSql;
            }

          }
          +

          这里眼尖的同学可能就可以看出来了，RawSqlSource 在初始化的时候已经经过了 parse，把#{}替换成了?占位符，但是 DynamicSqlSource 并没有
          再看这个图，我们发现在这的时候还没有进行替换
          然后往里跟
          好像是这里了

          这里 rootSqlNode.apply 其实是一个对原来 sql 的解析结果的一个循环调用，不同类型的标签会构成不同的 node，像这里就是一个 textSqlNode

          可以发现到这我们的 sql 已经被替换了，而且是直接作为 string 类型替换的，所以可以明白了这个问题所在，就是注入，不过细心的同学发现其实这里是有个

          理论上还是可以做过滤的，不过好像现在没用起来。
          我们前面可以发现对于#{}是在启动扫描 mapper的 xml 文件就替换成了 ?,然后是在什么时候变成实际的值的呢

          发现到这的时候还是没有替换，其实说白了也就是 prepareStatement 那一套，

          在这里进行替换，会拿到 org.apache.ibatis.mapping.ParameterMapping，然后进行替换，因为会带着类型信息，所以不用担心注入咯

          + + +
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          @@ -661,126 +776,10 @@ - - - -
          - - - - - -
          -

          - - -

          - -
          - - - - - Posted on - - - - - - - - Edited on - - - - - - - In - - - - , - - - - , - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
          -
          - - - - -
          - - -

          原谅我的标题党，其实这些工具的确很厉害，之前其实介绍过一点相关的，是从我一次问题排查的过程中用到的，但是最近又有碰到一次排查问题，发现其实用 idea 直接 dump thread 是不现实的，毕竟服务器环境的没法这么操作，那就得用 Java 的那些工具了

          -

          jstack & jps

          譬如 jstack，这个命令其实不能更简单了
          看看 help 信息

          用-l参数可以打出锁的额外信息，然后后面的 pid 就是进程 id 咯，机智的小伙伴会问了（就你这个小白才问这么蠢的问题🤦‍♂️），怎么看 Java 应用的进程呢
          那就是 jps 了，命令也很简单，一般直接用 jps命令就好了，不过也可以 help 看一下

          稍微解释下，-q是只显示进程 id，-m是输出给main 方法的参数，比如我在配置中加给参数

          然后用 jps -m查看

          -v加上小 v 的话就是打印 jvm 参数

          还是有点东西，然后就继续介绍 jstack 了，然后我们看看 jstack 出来是啥，为了加点内容我加了个死锁

          -
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          public static void main(String[] args) throws InterruptedException {
                  SpringApplication.run(ThreadDumpDemoApplication.class, args);
                  ReentrantLock lock1 = new ReentrantLock();
                  ReentrantLock lock2 = new ReentrantLock();
                  Thread t1 = new Thread() {
                      @Override
                      public void run() {
                          try {
                              lock1.lock();
                              TimeUnit.SECONDS.sleep(1);
                              lock2.lock();
                          } catch (InterruptedException e) {
                              e.printStackTrace();
                          }
                      }
                  };
                  Thread t2 = new Thread() {
                      @Override
                      public void run() {
                          try {
                              lock2.lock();
                              TimeUnit.SECONDS.sleep(1);
                              lock1.lock();
                          } catch (InterruptedException e) {
                              e.printStackTrace();
                          }
                      }
                  };
                  t1.setName("mythread1");
                  t2.setName("mythread2");
                  t1.start();
                  t2.start();
                  Thread.sleep(10000);
              }
          -

          然后看看出来时怎么样的

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          2020-08-02 21:50:32
          Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.201-b09 mixed mode):

          "DestroyJavaVM" #147 prio=5 os_prio=31 tid=0x00007fc9dd807000 nid=0x2603 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "mythread2" #140 prio=5 os_prio=31 tid=0x00007fc9dd877000 nid=0x9903 waiting on condition [0x0000700006fb9000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$2.run(ThreadDumpDemoApplication.java:34)

             Locked ownable synchronizers:
                  - <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

          "mythread1" #139 prio=5 os_prio=31 tid=0x00007fc9de873800 nid=0x9a03 waiting on condition [0x0000700006eb6000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$1.run(ThreadDumpDemoApplication.java:22)

             Locked ownable synchronizers:
                  - <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

          "http-nio-8080-Acceptor" #137 daemon prio=5 os_prio=31 tid=0x00007fc9de1ac000 nid=0x9b03 runnable [0x0000700006db3000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
                  at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
                  at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
                  - locked <0x000000076f1e4820> (a java.lang.Object)
                  at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:469)
                  at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:71)
                  at org.apache.tomcat.util.net.Acceptor.run(Acceptor.java:95)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-ClientPoller" #136 daemon prio=5 os_prio=31 tid=0x00007fc9dd876800 nid=0x6503 runnable [0x0000700006cb0000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.KQueueArrayWrapper.kevent0(Native Method)
                  at sun.nio.ch.KQueueArrayWrapper.poll(KQueueArrayWrapper.java:198)
                  at sun.nio.ch.KQueueSelectorImpl.doSelect(KQueueSelectorImpl.java:117)
                  at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
                  - locked <0x000000076f2978c8> (a sun.nio.ch.Util$3)
                  - locked <0x000000076f2978b8> (a java.util.Collections$UnmodifiableSet)
                  - locked <0x000000076f297798> (a sun.nio.ch.KQueueSelectorImpl)
                  at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
                  at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:709)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-10" #135 daemon prio=5 os_prio=31 tid=0x00007fc9de1af000 nid=0x9d03 waiting on condition [0x0000700006bad000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-9" #134 daemon prio=5 os_prio=31 tid=0x00007fc9de1ab800 nid=0x6403 waiting on condition [0x0000700006aaa000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-8" #133 daemon prio=5 os_prio=31 tid=0x00007fc9de873000 nid=0x9f03 waiting on condition [0x00007000069a7000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-7" #132 daemon prio=5 os_prio=31 tid=0x00007fc9df0a1800 nid=0xa103 waiting on condition [0x00007000068a4000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-6" #131 daemon prio=5 os_prio=31 tid=0x00007fc9df242800 nid=0x6103 waiting on condition [0x00007000067a1000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-5" #130 daemon prio=5 os_prio=31 tid=0x00007fc9de872000 nid=0x5f03 waiting on condition [0x000070000669e000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-4" #129 daemon prio=5 os_prio=31 tid=0x00007fc9de1a6000 nid=0x5e03 waiting on condition [0x000070000659b000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-3" #128 daemon prio=5 os_prio=31 tid=0x00007fc9de871800 nid=0x5c03 waiting on condition [0x0000700006498000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-2" #127 daemon prio=5 os_prio=31 tid=0x00007fc9dead9000 nid=0x5b03 waiting on condition [0x0000700006395000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-1" #126 daemon prio=5 os_prio=31 tid=0x00007fc9ddb00000 nid=0x5a03 waiting on condition [0x0000700006292000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-BlockPoller" #125 daemon prio=5 os_prio=31 tid=0x00007fc9df242000 nid=0xa503 runnable [0x000070000618f000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.KQueueArrayWrapper.kevent0(Native Method)
                  at sun.nio.ch.KQueueArrayWrapper.poll(KQueueArrayWrapper.java:198)
                  at sun.nio.ch.KQueueSelectorImpl.doSelect(KQueueSelectorImpl.java:117)
                  at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
                  - locked <0x000000076f1eea30> (a sun.nio.ch.Util$3)
                  - locked <0x000000076f1ee198> (a java.util.Collections$UnmodifiableSet)
                  - locked <0x000000076f1ee010> (a sun.nio.ch.KQueueSelectorImpl)
                  at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
                  at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:313)

             Locked ownable synchronizers:
                  - None

          "container-0" #124 prio=5 os_prio=31 tid=0x00007fc9df06a000 nid=0x5803 waiting on condition [0x000070000608c000]
             java.lang.Thread.State: TIMED_WAITING (sleeping)
                  at java.lang.Thread.sleep(Native Method)
                  at org.apache.catalina.core.StandardServer.await(StandardServer.java:570)
                  at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:197)

             Locked ownable synchronizers:
                  - None

          "Catalina-utility-2" #123 prio=1 os_prio=31 tid=0x00007fc9de886000 nid=0xa80f waiting on condition [0x0000700005f89000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076c88ab58> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1088)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Catalina-utility-1" #122 prio=1 os_prio=31 tid=0x00007fc9de884000 nid=0x5667 waiting on condition [0x0000700005e86000]
             java.lang.Thread.State: TIMED_WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076c88ab58> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "RMI Scheduler(0)" #15 daemon prio=5 os_prio=31 tid=0x00007fc9de9ee000 nid=0x5503 waiting on condition [0x0000700005d83000]
             java.lang.Thread.State: TIMED_WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x00000006c0015410> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Attach Listener" #13 daemon prio=9 os_prio=31 tid=0x00007fc9df149800 nid=0x3c07 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "RMI TCP Accept-0" #11 daemon prio=5 os_prio=31 tid=0x00007fc9df100000 nid=0x4003 runnable [0x0000700005977000]
             java.lang.Thread.State: RUNNABLE
                  at java.net.PlainSocketImpl.socketAccept(Native Method)
                  at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)
                  at java.net.ServerSocket.implAccept(ServerSocket.java:545)
                  at java.net.ServerSocket.accept(ServerSocket.java:513)
                  at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)
                  at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:405)
                  at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:377)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fc9df0ce800 nid=0x4103 runnable [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C1 CompilerThread2" #8 daemon prio=9 os_prio=31 tid=0x00007fc9df0ce000 nid=0x4203 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C2 CompilerThread1" #7 daemon prio=9 os_prio=31 tid=0x00007fc9de0a3800 nid=0x3503 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C2 CompilerThread0" #6 daemon prio=9 os_prio=31 tid=0x00007fc9de89b000 nid=0x3403 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "Monitor Ctrl-Break" #5 daemon prio=5 os_prio=31 tid=0x00007fc9df0ca000 nid=0x3303 runnable [0x0000700005468000]
             java.lang.Thread.State: RUNNABLE
                  at java.net.SocketInputStream.socketRead0(Native Method)
                  at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
                  at java.net.SocketInputStream.read(SocketInputStream.java:171)
                  at java.net.SocketInputStream.read(SocketInputStream.java:141)
                  at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
                  at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
                  at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
                  - locked <0x00000006c001b760> (a java.io.InputStreamReader)
                  at java.io.InputStreamReader.read(InputStreamReader.java:184)
                  at java.io.BufferedReader.fill(BufferedReader.java:161)
                  at java.io.BufferedReader.readLine(BufferedReader.java:324)
                  - locked <0x00000006c001b760> (a java.io.InputStreamReader)
                  at java.io.BufferedReader.readLine(BufferedReader.java:389)
                  at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)

             Locked ownable synchronizers:
                  - None

          "Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fc9de824000 nid=0x4503 runnable [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fc9dd811800 nid=0x4f03 in Object.wait() [0x0000700005262000]
             java.lang.Thread.State: WAITING (on object monitor)
                  at java.lang.Object.wait(Native Method)
                  - waiting on <0x00000006c0008348> (a java.lang.ref.ReferenceQueue$Lock)
                  at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
                  - locked <0x00000006c0008348> (a java.lang.ref.ReferenceQueue$Lock)
                  at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
                  at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

             Locked ownable synchronizers:
                  - None

          "Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fc9de02a000 nid=0x5003 in Object.wait() [0x000070000515f000]
             java.lang.Thread.State: WAITING (on object monitor)
                  at java.lang.Object.wait(Native Method)
                  - waiting on <0x00000006c001b940> (a java.lang.ref.Reference$Lock)
                  at java.lang.Object.wait(Object.java:502)
                  at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
                  - locked <0x00000006c001b940> (a java.lang.ref.Reference$Lock)
                  at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

             Locked ownable synchronizers:
                  - None

          "VM Thread" os_prio=31 tid=0x00007fc9df00b800 nid=0x2c03 runnable 

          "GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fc9de805000 nid=0x1e07 runnable 

          "GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fc9de003800 nid=0x2a03 runnable 

          "GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fc9df002000 nid=0x5403 runnable 

          "GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fc9df002800 nid=0x5203 runnable 

          "VM Periodic Task Thread" os_prio=31 tid=0x00007fc9df11a800 nid=0x3a03 waiting on condition 

          JNI global references: 1087


          Found one Java-level deadlock:
          =============================
          "mythread2":
            waiting for ownable synchronizer 0x000000076f5d4330, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
            which is held by "mythread1"
          "mythread1":
            waiting for ownable synchronizer 0x000000076f5d4360, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
            which is held by "mythread2"

          Java stack information for the threads listed above:
          ===================================================
          "mythread2":
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$2.run(ThreadDumpDemoApplication.java:34)
          "mythread1":
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$1.run(ThreadDumpDemoApplication.java:22)

          Found 1 deadlock.
          -

          前面的信息其实上次就看过了，后面就可以发现有个死锁了，

          上面比较长，把主要的截出来，就是这边的，这点就很强大了。

          -

          jmap

          惯例还是看一下帮助信息

          这个相对命令比较多，不过因为现在 dump 下来我们可能会用文件模式，然后将文件下载下来使用 mat 进行分析，所以可以使用
          jmap -dump:live,format=b,file=heap.bin <pid>
          命令照着上面看的就是打印活着的对象，然后以二进制格式，文件名叫 heap.bin 然后最后就是进程 id，打印出来以后可以用 mat 打开

          这样就可以很清晰的看到应用里的各种信息，jmap 直接在命令中还可以看很多信息，比如使用jmap -histo <pid>打印对象的实例数和对象占用的内存

          jmap -finalizerinfo <pid> 打印正在等候回收的对象

          -

          小tips

          对于一些应用内存已经占满了，jstack 和 jmap 可能会连不上的情况，可以使用-F参数强制打印线程或者 dump 文件，但是要注意这两者使用的用户必须与 java 进程启动用户一致，并且使用的 jdk 也要一致

          - - -
          - - - - - - -
          -
          -
          -
          - - - - @@ -848,20 +847,20 @@
          - 70 + 71 posts
          - 81 + 83 categories
          - 113 + 114 tags
          @@ -886,7 +885,7 @@
          - +
          diff --git a/page/3/index.html b/page/3/index.html index 11cbc5713e..27875d3e6b 100644 --- a/page/3/index.html +++ b/page/3/index.html @@ -203,6 +203,122 @@ +
          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + Edited on + + + + + + + In + + + + , + + + + , + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          原谅我的标题党，其实这些工具的确很厉害，之前其实介绍过一点相关的，是从我一次问题排查的过程中用到的，但是最近又有碰到一次排查问题，发现其实用 idea 直接 dump thread 是不现实的，毕竟服务器环境的没法这么操作，那就得用 Java 的那些工具了

          +

          jstack & jps

          譬如 jstack，这个命令其实不能更简单了
          看看 help 信息

          用-l参数可以打出锁的额外信息，然后后面的 pid 就是进程 id 咯，机智的小伙伴会问了（就你这个小白才问这么蠢的问题🤦‍♂️），怎么看 Java 应用的进程呢
          那就是 jps 了，命令也很简单，一般直接用 jps命令就好了，不过也可以 help 看一下

          稍微解释下，-q是只显示进程 id，-m是输出给main 方法的参数，比如我在配置中加给参数

          然后用 jps -m查看

          -v加上小 v 的话就是打印 jvm 参数

          还是有点东西，然后就继续介绍 jstack 了，然后我们看看 jstack 出来是啥，为了加点内容我加了个死锁

          +
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          public static void main(String[] args) throws InterruptedException {
                  SpringApplication.run(ThreadDumpDemoApplication.class, args);
                  ReentrantLock lock1 = new ReentrantLock();
                  ReentrantLock lock2 = new ReentrantLock();
                  Thread t1 = new Thread() {
                      @Override
                      public void run() {
                          try {
                              lock1.lock();
                              TimeUnit.SECONDS.sleep(1);
                              lock2.lock();
                          } catch (InterruptedException e) {
                              e.printStackTrace();
                          }
                      }
                  };
                  Thread t2 = new Thread() {
                      @Override
                      public void run() {
                          try {
                              lock2.lock();
                              TimeUnit.SECONDS.sleep(1);
                              lock1.lock();
                          } catch (InterruptedException e) {
                              e.printStackTrace();
                          }
                      }
                  };
                  t1.setName("mythread1");
                  t2.setName("mythread2");
                  t1.start();
                  t2.start();
                  Thread.sleep(10000);
              }
          +

          然后看看出来时怎么样的

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          2020-08-02 21:50:32
          Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.201-b09 mixed mode):

          "DestroyJavaVM" #147 prio=5 os_prio=31 tid=0x00007fc9dd807000 nid=0x2603 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "mythread2" #140 prio=5 os_prio=31 tid=0x00007fc9dd877000 nid=0x9903 waiting on condition [0x0000700006fb9000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$2.run(ThreadDumpDemoApplication.java:34)

             Locked ownable synchronizers:
                  - <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

          "mythread1" #139 prio=5 os_prio=31 tid=0x00007fc9de873800 nid=0x9a03 waiting on condition [0x0000700006eb6000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$1.run(ThreadDumpDemoApplication.java:22)

             Locked ownable synchronizers:
                  - <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

          "http-nio-8080-Acceptor" #137 daemon prio=5 os_prio=31 tid=0x00007fc9de1ac000 nid=0x9b03 runnable [0x0000700006db3000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
                  at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
                  at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
                  - locked <0x000000076f1e4820> (a java.lang.Object)
                  at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:469)
                  at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:71)
                  at org.apache.tomcat.util.net.Acceptor.run(Acceptor.java:95)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-ClientPoller" #136 daemon prio=5 os_prio=31 tid=0x00007fc9dd876800 nid=0x6503 runnable [0x0000700006cb0000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.KQueueArrayWrapper.kevent0(Native Method)
                  at sun.nio.ch.KQueueArrayWrapper.poll(KQueueArrayWrapper.java:198)
                  at sun.nio.ch.KQueueSelectorImpl.doSelect(KQueueSelectorImpl.java:117)
                  at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
                  - locked <0x000000076f2978c8> (a sun.nio.ch.Util$3)
                  - locked <0x000000076f2978b8> (a java.util.Collections$UnmodifiableSet)
                  - locked <0x000000076f297798> (a sun.nio.ch.KQueueSelectorImpl)
                  at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
                  at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:709)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-10" #135 daemon prio=5 os_prio=31 tid=0x00007fc9de1af000 nid=0x9d03 waiting on condition [0x0000700006bad000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-9" #134 daemon prio=5 os_prio=31 tid=0x00007fc9de1ab800 nid=0x6403 waiting on condition [0x0000700006aaa000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-8" #133 daemon prio=5 os_prio=31 tid=0x00007fc9de873000 nid=0x9f03 waiting on condition [0x00007000069a7000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-7" #132 daemon prio=5 os_prio=31 tid=0x00007fc9df0a1800 nid=0xa103 waiting on condition [0x00007000068a4000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-6" #131 daemon prio=5 os_prio=31 tid=0x00007fc9df242800 nid=0x6103 waiting on condition [0x00007000067a1000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-5" #130 daemon prio=5 os_prio=31 tid=0x00007fc9de872000 nid=0x5f03 waiting on condition [0x000070000669e000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-4" #129 daemon prio=5 os_prio=31 tid=0x00007fc9de1a6000 nid=0x5e03 waiting on condition [0x000070000659b000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-3" #128 daemon prio=5 os_prio=31 tid=0x00007fc9de871800 nid=0x5c03 waiting on condition [0x0000700006498000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-2" #127 daemon prio=5 os_prio=31 tid=0x00007fc9dead9000 nid=0x5b03 waiting on condition [0x0000700006395000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-exec-1" #126 daemon prio=5 os_prio=31 tid=0x00007fc9ddb00000 nid=0x5a03 waiting on condition [0x0000700006292000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f26aa00> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
                  at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "http-nio-8080-BlockPoller" #125 daemon prio=5 os_prio=31 tid=0x00007fc9df242000 nid=0xa503 runnable [0x000070000618f000]
             java.lang.Thread.State: RUNNABLE
                  at sun.nio.ch.KQueueArrayWrapper.kevent0(Native Method)
                  at sun.nio.ch.KQueueArrayWrapper.poll(KQueueArrayWrapper.java:198)
                  at sun.nio.ch.KQueueSelectorImpl.doSelect(KQueueSelectorImpl.java:117)
                  at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
                  - locked <0x000000076f1eea30> (a sun.nio.ch.Util$3)
                  - locked <0x000000076f1ee198> (a java.util.Collections$UnmodifiableSet)
                  - locked <0x000000076f1ee010> (a sun.nio.ch.KQueueSelectorImpl)
                  at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
                  at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:313)

             Locked ownable synchronizers:
                  - None

          "container-0" #124 prio=5 os_prio=31 tid=0x00007fc9df06a000 nid=0x5803 waiting on condition [0x000070000608c000]
             java.lang.Thread.State: TIMED_WAITING (sleeping)
                  at java.lang.Thread.sleep(Native Method)
                  at org.apache.catalina.core.StandardServer.await(StandardServer.java:570)
                  at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:197)

             Locked ownable synchronizers:
                  - None

          "Catalina-utility-2" #123 prio=1 os_prio=31 tid=0x00007fc9de886000 nid=0xa80f waiting on condition [0x0000700005f89000]
             java.lang.Thread.State: WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076c88ab58> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1088)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Catalina-utility-1" #122 prio=1 os_prio=31 tid=0x00007fc9de884000 nid=0x5667 waiting on condition [0x0000700005e86000]
             java.lang.Thread.State: TIMED_WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076c88ab58> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "RMI Scheduler(0)" #15 daemon prio=5 os_prio=31 tid=0x00007fc9de9ee000 nid=0x5503 waiting on condition [0x0000700005d83000]
             java.lang.Thread.State: TIMED_WAITING (parking)
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x00000006c0015410> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
                  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
                  at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
                  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Attach Listener" #13 daemon prio=9 os_prio=31 tid=0x00007fc9df149800 nid=0x3c07 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "RMI TCP Accept-0" #11 daemon prio=5 os_prio=31 tid=0x00007fc9df100000 nid=0x4003 runnable [0x0000700005977000]
             java.lang.Thread.State: RUNNABLE
                  at java.net.PlainSocketImpl.socketAccept(Native Method)
                  at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)
                  at java.net.ServerSocket.implAccept(ServerSocket.java:545)
                  at java.net.ServerSocket.accept(ServerSocket.java:513)
                  at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)
                  at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:405)
                  at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:377)
                  at java.lang.Thread.run(Thread.java:748)

             Locked ownable synchronizers:
                  - None

          "Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fc9df0ce800 nid=0x4103 runnable [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C1 CompilerThread2" #8 daemon prio=9 os_prio=31 tid=0x00007fc9df0ce000 nid=0x4203 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C2 CompilerThread1" #7 daemon prio=9 os_prio=31 tid=0x00007fc9de0a3800 nid=0x3503 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "C2 CompilerThread0" #6 daemon prio=9 os_prio=31 tid=0x00007fc9de89b000 nid=0x3403 waiting on condition [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "Monitor Ctrl-Break" #5 daemon prio=5 os_prio=31 tid=0x00007fc9df0ca000 nid=0x3303 runnable [0x0000700005468000]
             java.lang.Thread.State: RUNNABLE
                  at java.net.SocketInputStream.socketRead0(Native Method)
                  at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
                  at java.net.SocketInputStream.read(SocketInputStream.java:171)
                  at java.net.SocketInputStream.read(SocketInputStream.java:141)
                  at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
                  at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
                  at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
                  - locked <0x00000006c001b760> (a java.io.InputStreamReader)
                  at java.io.InputStreamReader.read(InputStreamReader.java:184)
                  at java.io.BufferedReader.fill(BufferedReader.java:161)
                  at java.io.BufferedReader.readLine(BufferedReader.java:324)
                  - locked <0x00000006c001b760> (a java.io.InputStreamReader)
                  at java.io.BufferedReader.readLine(BufferedReader.java:389)
                  at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)

             Locked ownable synchronizers:
                  - None

          "Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fc9de824000 nid=0x4503 runnable [0x0000000000000000]
             java.lang.Thread.State: RUNNABLE

             Locked ownable synchronizers:
                  - None

          "Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fc9dd811800 nid=0x4f03 in Object.wait() [0x0000700005262000]
             java.lang.Thread.State: WAITING (on object monitor)
                  at java.lang.Object.wait(Native Method)
                  - waiting on <0x00000006c0008348> (a java.lang.ref.ReferenceQueue$Lock)
                  at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
                  - locked <0x00000006c0008348> (a java.lang.ref.ReferenceQueue$Lock)
                  at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
                  at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

             Locked ownable synchronizers:
                  - None

          "Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fc9de02a000 nid=0x5003 in Object.wait() [0x000070000515f000]
             java.lang.Thread.State: WAITING (on object monitor)
                  at java.lang.Object.wait(Native Method)
                  - waiting on <0x00000006c001b940> (a java.lang.ref.Reference$Lock)
                  at java.lang.Object.wait(Object.java:502)
                  at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
                  - locked <0x00000006c001b940> (a java.lang.ref.Reference$Lock)
                  at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

             Locked ownable synchronizers:
                  - None

          "VM Thread" os_prio=31 tid=0x00007fc9df00b800 nid=0x2c03 runnable 

          "GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fc9de805000 nid=0x1e07 runnable 

          "GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fc9de003800 nid=0x2a03 runnable 

          "GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fc9df002000 nid=0x5403 runnable 

          "GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fc9df002800 nid=0x5203 runnable 

          "VM Periodic Task Thread" os_prio=31 tid=0x00007fc9df11a800 nid=0x3a03 waiting on condition 

          JNI global references: 1087


          Found one Java-level deadlock:
          =============================
          "mythread2":
            waiting for ownable synchronizer 0x000000076f5d4330, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
            which is held by "mythread1"
          "mythread1":
            waiting for ownable synchronizer 0x000000076f5d4360, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
            which is held by "mythread2"

          Java stack information for the threads listed above:
          ===================================================
          "mythread2":
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4330> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$2.run(ThreadDumpDemoApplication.java:34)
          "mythread1":
                  at sun.misc.Unsafe.park(Native Method)
                  - parking to wait for  <0x000000076f5d4360> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
                  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
                  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
                  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
                  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
                  at com.nicksxs.thread_dump_demo.ThreadDumpDemoApplication$1.run(ThreadDumpDemoApplication.java:22)

          Found 1 deadlock.
          +

          前面的信息其实上次就看过了，后面就可以发现有个死锁了，

          上面比较长，把主要的截出来，就是这边的，这点就很强大了。

          +

          jmap

          惯例还是看一下帮助信息

          这个相对命令比较多，不过因为现在 dump 下来我们可能会用文件模式，然后将文件下载下来使用 mat 进行分析，所以可以使用
          jmap -dump:live,format=b,file=heap.bin <pid>
          命令照着上面看的就是打印活着的对象，然后以二进制格式，文件名叫 heap.bin 然后最后就是进程 id，打印出来以后可以用 mat 打开

          这样就可以很清晰的看到应用里的各种信息，jmap 直接在命令中还可以看很多信息，比如使用jmap -histo <pid>打印对象的实例数和对象占用的内存

          jmap -finalizerinfo <pid> 打印正在等候回收的对象

          +

          小tips

          对于一些应用内存已经占满了，jstack 和 jmap 可能会连不上的情况，可以使用-F参数强制打印线程或者 dump 文件，但是要注意这两者使用的用户必须与 java 进程启动用户一致，并且使用的 jdk 也要一致

          + + +
          + + + + + + +
          +
          +
          +
          + + + + + + +
          @@ -725,158 +841,10 @@ - - - -
          - - - - - -
          -

          - - -

          - -
          - - - - - Posted on - - - - - - - - Edited on - - - - - - - In - - - - , - - - - , - - - - , - - - - , - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
          -
          - - - - -
          - - -

          首先看下官方的小 demo

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          public static void main(String[] args) throws InterruptedException, MQClientException {

                  /*
                   * Instantiate with specified consumer group name.
                   * 首先是new 一个对象出来，然后指定 Consumer 的 Group
                   * 同一类Consumer的集合，这类Consumer通常消费同一类消息且消费逻辑一致。消费者组使得在消息消费方面，实现负载均衡和容错的目标变得非常容易。要注意的是，消费者组的消费者实例必须订阅完全相同的Topic。RocketMQ 支持两种消息模式：集群消费（Clustering）和广播消费（Broadcasting）。
                   */
                  DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name_4");

                  /*
                   * Specify name server addresses.
                   * <p/>
                   * 这里可以通知指定环境变量或者设置对象参数的形式指定名字空间服务的地址
                   *
                   * Alternatively, you may specify name server addresses via exporting environmental variable: NAMESRV_ADDR
                   * <pre>
                   * {@code
                   * consumer.setNamesrvAddr("name-server1-ip:9876;name-server2-ip:9876");
                   * }
                   * </pre>
                   */

                  /*
                   * Specify where to start in case the specified consumer group is a brand new one.
                   * 指定消费起始点
                   */
                  consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);

                  /*
                   * Subscribe one more more topics to consume.
                   * 指定订阅的 topic 跟 tag，注意后面的是个表达式，可以以 tag1 || tag2 || tag3 传入
                   */
                  consumer.subscribe("TopicTest", "*");

                  /*
                   *  Register callback to execute on arrival of messages fetched from brokers.
                   *  注册具体获得消息后的处理方法
                   */
                  consumer.registerMessageListener(new MessageListenerConcurrently() {

                      @Override
                      public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs,
                          ConsumeConcurrentlyContext context) {
                          System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
                          return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
                      }
                  });

                  /*
                   *  Launch the consumer instance.
                   * 启动消费者
                   */
                  consumer.start();

                  System.out.printf("Consumer Started.%n");
              }
          - -

          然后就是看看 start 的过程了

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          /**
               * This method gets internal infrastructure readily to serve. Instances must call this method after configuration.
               *
               * @throws MQClientException if there is any client error.
               */
              @Override
              public void start() throws MQClientException {
                  setConsumerGroup(NamespaceUtil.wrapNamespace(this.getNamespace(), this.consumerGroup));
                  this.defaultMQPushConsumerImpl.start();
                  if (null != traceDispatcher) {
                      try {
                          traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
                      } catch (MQClientException e) {
                          log.warn("trace dispatcher start failed ", e);
                      }
                  }
              }
          -

          具体的逻辑在this.defaultMQPushConsumerImpl.start()，这个 defaultMQPushConsumerImpl 就是

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          /**
               * Internal implementation. Most of the functions herein are delegated to it.
               */
              protected final transient DefaultMQPushConsumerImpl defaultMQPushConsumerImpl;
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          public synchronized void start() throws MQClientException {
                  switch (this.serviceState) {
                      case CREATE_JUST:
                          log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),
                              this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());
                          // 这里比较巧妙，相当于想设立了个屏障，防止并发启动，不过这里并不是悲观锁，也不算个严格的乐观锁
                          this.serviceState = ServiceState.START_FAILED;

                          this.checkConfig();

                          this.copySubscription();

                          if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
                              this.defaultMQPushConsumer.changeInstanceNameToPID();
                          }

                          // 这个mQClientFactory，负责管理client（consumer、producer），并提供多中功能接口供各个Service（Rebalance、PullMessage等）调用；大部分逻辑均在这个类中完成
                          this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);

                          // 这个 rebalanceImpl 主要负责决定，当前的consumer应该从哪些Queue中消费消息；
                          this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
                          this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
                          this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
                          this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);

                          // 长连接，负责从broker处拉取消息，然后利用ConsumeMessageService回调用户的Listener执行消息消费逻辑
                          this.pullAPIWrapper = new PullAPIWrapper(
                              mQClientFactory,
                              this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
                          this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);

                          if (this.defaultMQPushConsumer.getOffsetStore() != null) {
                              this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
                          } else {
                              switch (this.defaultMQPushConsumer.getMessageModel()) {
                                  case BROADCASTING:
                                      this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
                                      break;
                                  case CLUSTERING:
                                      this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
                                      break;
                                  default:
                                      break;
                              }
                              this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);
                          }
                          // offsetStore 维护当前consumer的消费记录（offset）；有两种实现，Local和Rmote，Local存储在本地磁盘上，适用于BROADCASTING广播消费模式；而Remote则将消费进度存储在Broker上，适用于CLUSTERING集群消费模式；
                          this.offsetStore.load();

                          if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
                              this.consumeOrderly = true;
                              this.consumeMessageService =
                                  new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
                          } else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
                              this.consumeOrderly = false;
                              this.consumeMessageService =
                                  new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
                          }

                          // 实现所谓的"Push-被动"消费机制；从Broker拉取的消息后，封装成ConsumeRequest提交给ConsumeMessageSerivce，此service负责回调用户的Listener消费消息；
                          this.consumeMessageService.start();

                          boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
                          if (!registerOK) {
                              this.serviceState = ServiceState.CREATE_JUST;
                              this.consumeMessageService.shutdown();
                              throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()
                                  + "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
                                  null);
                          }

                          mQClientFactory.start();
                          log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());
                          this.serviceState = ServiceState.RUNNING;
                          break;
                      case RUNNING:
                      case START_FAILED:
                      case SHUTDOWN_ALREADY:
                          throw new MQClientException("The PushConsumer service state not OK, maybe started once, "
                              + this.serviceState
                              + FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
                              null);
                      default:
                          break;
                  }

                  this.updateTopicSubscribeInfoWhenSubscriptionChanged();
                  this.mQClientFactory.checkClientInBroker();
                  this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
                  this.mQClientFactory.rebalanceImmediately();
              }
          -

          然后我们往下看主要的目光聚焦mQClientFactory.start()

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          public void start() throws MQClientException {

                  synchronized (this) {
                      switch (this.serviceState) {
                          case CREATE_JUST:
                              this.serviceState = ServiceState.START_FAILED;
                              // If not specified,looking address from name server
                              if (null == this.clientConfig.getNamesrvAddr()) {
                                  this.mQClientAPIImpl.fetchNameServerAddr();
                              }
                              // Start request-response channel
                              // 这里主要是初始化了个网络客户端
                              this.mQClientAPIImpl.start();
                              // Start various schedule tasks
                              // 定时任务
                              this.startScheduledTask();
                              // Start pull service
                              // 这里重点说下
                              this.pullMessageService.start();
                              // Start rebalance service
                              this.rebalanceService.start();
                              // Start push service
                              this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
                              log.info("the client factory [{}] start OK", this.clientId);
                              this.serviceState = ServiceState.RUNNING;
                              break;
                          case START_FAILED:
                              throw new MQClientException("The Factory object[" + this.getClientId() + "] has been created before, and failed.", null);
                          default:
                              break;
                      }
                  }
              }
          -

          我们来看下这个 pullMessageService，org.apache.rocketmq.client.impl.consumer.PullMessageService，

          实现了 runnable 接口，
          然后可以看到 run 方法

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          public void run() {
                  log.info(this.getServiceName() + " service started");

                  while (!this.isStopped()) {
                      try {
                          PullRequest pullRequest = this.pullRequestQueue.take();
                          this.pullMessage(pullRequest);
                      } catch (InterruptedException ignored) {
                      } catch (Exception e) {
                          log.error("Pull Message Service Run Method exception", e);
                      }
                  }

                  log.info(this.getServiceName() + " service end");
              }
          -

          接着在看 pullMessage 方法

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          private void pullMessage(final PullRequest pullRequest) {
                  final MQConsumerInner consumer = this.mQClientFactory.selectConsumer(pullRequest.getConsumerGroup());
                  if (consumer != null) {
                      DefaultMQPushConsumerImpl impl = (DefaultMQPushConsumerImpl) consumer;
                      impl.pullMessage(pullRequest);
                  } else {
                      log.warn("No matched consumer for the PullRequest {}, drop it", pullRequest);
                  }
              }
          -

          实际上调用了这个方法，这个方法很长，我在代码里注释下下每一段的功能

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          public void pullMessage(final PullRequest pullRequest) {
                  final ProcessQueue processQueue = pullRequest.getProcessQueue();
                  // 这里开始就是检查状态，确定是否往下执行
                  if (processQueue.isDropped()) {
                      log.info("the pull request[{}] is dropped.", pullRequest.toString());
                      return;
                  }

                  pullRequest.getProcessQueue().setLastPullTimestamp(System.currentTimeMillis());

                  try {
                      this.makeSureStateOK();
                  } catch (MQClientException e) {
                      log.warn("pullMessage exception, consumer state not ok", e);
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      return;
                  }

                  if (this.isPause()) {
                      log.warn("consumer was paused, execute pull request later. instanceName={}, group={}", this.defaultMQPushConsumer.getInstanceName(), this.defaultMQPushConsumer.getConsumerGroup());
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_SUSPEND);
                      return;
                  }

                  // 这块其实是个类似于限流的功能块，对消息数量和消息大小做限制
                  long cachedMessageCount = processQueue.getMsgCount().get();
                  long cachedMessageSizeInMiB = processQueue.getMsgSize().get() / (1024 * 1024);

                  if (cachedMessageCount > this.defaultMQPushConsumer.getPullThresholdForQueue()) {
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                      if ((queueFlowControlTimes++ % 1000) == 0) {
                          log.warn(
                              "the cached message count exceeds the threshold {}, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
                              this.defaultMQPushConsumer.getPullThresholdForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
                      }
                      return;
                  }

                  if (cachedMessageSizeInMiB > this.defaultMQPushConsumer.getPullThresholdSizeForQueue()) {
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                      if ((queueFlowControlTimes++ % 1000) == 0) {
                          log.warn(
                              "the cached message size exceeds the threshold {} MiB, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
                              this.defaultMQPushConsumer.getPullThresholdSizeForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
                      }
                      return;
                  }

                  // 若不是顺序消费（即DefaultMQPushConsumerImpl.consumeOrderly等于false），则检查ProcessQueue对象的msgTreeMap:TreeMap<Long,MessageExt>变量的第一个key值与最后一个key值之间的差额，该key值表示查询的队列偏移量queueoffset；若差额大于阈值（由DefaultMQPushConsumer. consumeConcurrentlyMaxSpan指定，默认是2000），则调用PullMessageService.executePullRequestLater方法，在50毫秒之后重新将该PullRequest请求放入PullMessageService.pullRequestQueue队列中；并跳出该方法；这里的意思主要就是消息有堆积了，等会再来拉取
                  if (!this.consumeOrderly) {
                      if (processQueue.getMaxSpan() > this.defaultMQPushConsumer.getConsumeConcurrentlyMaxSpan()) {
                          this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                          if ((queueMaxSpanFlowControlTimes++ % 1000) == 0) {
                              log.warn(
                                  "the queue's messages, span too long, so do flow control, minOffset={}, maxOffset={}, maxSpan={}, pullRequest={}, flowControlTimes={}",
                                  processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), processQueue.getMaxSpan(),
                                  pullRequest, queueMaxSpanFlowControlTimes);
                          }
                          return;
                      }
                  } else {
                      if (processQueue.isLocked()) {
                          if (!pullRequest.isLockedFirst()) {
                              final long offset = this.rebalanceImpl.computePullFromWhere(pullRequest.getMessageQueue());
                              boolean brokerBusy = offset < pullRequest.getNextOffset();
                              log.info("the first time to pull message, so fix offset from broker. pullRequest: {} NewOffset: {} brokerBusy: {}",
                                  pullRequest, offset, brokerBusy);
                              if (brokerBusy) {
                                  log.info("[NOTIFYME]the first time to pull message, but pull request offset larger than broker consume offset. pullRequest: {} NewOffset: {}",
                                      pullRequest, offset);
                              }

                              pullRequest.setLockedFirst(true);
                              pullRequest.setNextOffset(offset);
                          }
                      } else {
                          this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                          log.info("pull message later because not locked in broker, {}", pullRequest);
                          return;
                      }
                  }

                  // 以PullRequest.messageQueue对象的topic值为参数从RebalanceImpl.subscriptionInner: ConcurrentHashMap, SubscriptionData>中获取对应的SubscriptionData对象，若该对象为null，考虑到并发的关系，调用executePullRequestLater方法，稍后重试；并跳出该方法；
                  final SubscriptionData subscriptionData = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
                  if (null == subscriptionData) {
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      log.warn("find the consumer's subscription failed, {}", pullRequest);
                      return;
                  }

                  final long beginTimestamp = System.currentTimeMillis();

                  // 异步拉取回调，先不讨论细节
                  PullCallback pullCallback = new PullCallback() {
                      @Override
                      public void onSuccess(PullResult pullResult) {
                          if (pullResult != null) {
                              pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult,
                                  subscriptionData);

                              switch (pullResult.getPullStatus()) {
                                  case FOUND:
                                      long prevRequestOffset = pullRequest.getNextOffset();
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());
                                      long pullRT = System.currentTimeMillis() - beginTimestamp;
                                      DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullRT(pullRequest.getConsumerGroup(),
                                          pullRequest.getMessageQueue().getTopic(), pullRT);

                                      long firstMsgOffset = Long.MAX_VALUE;
                                      if (pullResult.getMsgFoundList() == null || pullResult.getMsgFoundList().isEmpty()) {
                                          DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      } else {
                                          firstMsgOffset = pullResult.getMsgFoundList().get(0).getQueueOffset();

                                          DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullTPS(pullRequest.getConsumerGroup(),
                                              pullRequest.getMessageQueue().getTopic(), pullResult.getMsgFoundList().size());

                                          boolean dispatchToConsume = processQueue.putMessage(pullResult.getMsgFoundList());
                                          DefaultMQPushConsumerImpl.this.consumeMessageService.submitConsumeRequest(
                                              pullResult.getMsgFoundList(),
                                              processQueue,
                                              pullRequest.getMessageQueue(),
                                              dispatchToConsume);

                                          if (DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval() > 0) {
                                              DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest,
                                                  DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval());
                                          } else {
                                              DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                          }
                                      }

                                      if (pullResult.getNextBeginOffset() < prevRequestOffset
                                          || firstMsgOffset < prevRequestOffset) {
                                          log.warn(
                                              "[BUG] pull message result maybe data wrong, nextBeginOffset: {} firstMsgOffset: {} prevRequestOffset: {}",
                                              pullResult.getNextBeginOffset(),
                                              firstMsgOffset,
                                              prevRequestOffset);
                                      }

                                      break;
                                  case NO_NEW_MSG:
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);

                                      DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      break;
                                  case NO_MATCHED_MSG:
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);

                                      DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      break;
                                  case OFFSET_ILLEGAL:
                                      log.warn("the pull request offset illegal, {} {}",
                                          pullRequest.toString(), pullResult.toString());
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      pullRequest.getProcessQueue().setDropped(true);
                                      DefaultMQPushConsumerImpl.this.executeTaskLater(new Runnable() {

                                          @Override
                                          public void run() {
                                              try {
                                                  DefaultMQPushConsumerImpl.this.offsetStore.updateOffset(pullRequest.getMessageQueue(),
                                                      pullRequest.getNextOffset(), false);

                                                  DefaultMQPushConsumerImpl.this.offsetStore.persist(pullRequest.getMessageQueue());

                                                  DefaultMQPushConsumerImpl.this.rebalanceImpl.removeProcessQueue(pullRequest.getMessageQueue());

                                                  log.warn("fix the pull request offset, {}", pullRequest);
                                              } catch (Throwable e) {
                                                  log.error("executeTaskLater Exception", e);
                                              }
                                          }
                                      }, 10000);
                                      break;
                                  default:
                                      break;
                              }
                          }
                      }

                      @Override
                      public void onException(Throwable e) {
                          if (!pullRequest.getMessageQueue().getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
                              log.warn("execute the pull request exception", e);
                          }

                          DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      }
                  };
                  // 如果为集群模式，即可置commitOffsetEnable为 true
                  boolean commitOffsetEnable = false;
                  long commitOffsetValue = 0L;
                  if (MessageModel.CLUSTERING == this.defaultMQPushConsumer.getMessageModel()) {
                      commitOffsetValue = this.offsetStore.readOffset(pullRequest.getMessageQueue(), ReadOffsetType.READ_FROM_MEMORY);
                      if (commitOffsetValue > 0) {
                          commitOffsetEnable = true;
                      }
                  }

                  // 将上面获得的commitOffsetEnable更新到订阅关系里
                  String subExpression = null;
                  boolean classFilter = false;
                  SubscriptionData sd = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
                  if (sd != null) {
                      if (this.defaultMQPushConsumer.isPostSubscriptionWhenPull() && !sd.isClassFilterMode()) {
                          subExpression = sd.getSubString();
                      }

                      classFilter = sd.isClassFilterMode();
                  }

                  // 组成 sysFlag
                  int sysFlag = PullSysFlag.buildSysFlag(
                      commitOffsetEnable, // commitOffset
                      true, // suspend
                      subExpression != null, // subscription
                      classFilter // class filter
                  );
                  // 调用真正的拉取消息接口
                  try {
                      this.pullAPIWrapper.pullKernelImpl(
                          pullRequest.getMessageQueue(),
                          subExpression,
                          subscriptionData.getExpressionType(),
                          subscriptionData.getSubVersion(),
                          pullRequest.getNextOffset(),
                          this.defaultMQPushConsumer.getPullBatchSize(),
                          sysFlag,
                          commitOffsetValue,
                          BROKER_SUSPEND_MAX_TIME_MILLIS,
                          CONSUMER_TIMEOUT_MILLIS_WHEN_SUSPEND,
                          CommunicationMode.ASYNC,
                          pullCallback
                      );
                  } catch (Exception e) {
                      log.error("pullKernelImpl exception", e);
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                  }
              }
          -

          以下就是拉取消息的底层 api，不够不是特别复杂，主要是在找 broker，和设置请求参数

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          public PullResult pullKernelImpl(
              final MessageQueue mq,
              final String subExpression,
              final String expressionType,
              final long subVersion,
              final long offset,
              final int maxNums,
              final int sysFlag,
              final long commitOffset,
              final long brokerSuspendMaxTimeMillis,
              final long timeoutMillis,
              final CommunicationMode communicationMode,
              final PullCallback pullCallback
          ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
              FindBrokerResult findBrokerResult =
                  this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                      this.recalculatePullFromWhichNode(mq), false);
              if (null == findBrokerResult) {
                  this.mQClientFactory.updateTopicRouteInfoFromNameServer(mq.getTopic());
                  findBrokerResult =
                      this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                          this.recalculatePullFromWhichNode(mq), false);
              }

              if (findBrokerResult != null) {
                  {
                      // check version
                      if (!ExpressionType.isTagType(expressionType)
                          && findBrokerResult.getBrokerVersion() < MQVersion.Version.V4_1_0_SNAPSHOT.ordinal()) {
                          throw new MQClientException("The broker[" + mq.getBrokerName() + ", "
                              + findBrokerResult.getBrokerVersion() + "] does not upgrade to support for filter message by " + expressionType, null);
                      }
                  }
                  int sysFlagInner = sysFlag;

                  if (findBrokerResult.isSlave()) {
                      sysFlagInner = PullSysFlag.clearCommitOffsetFlag(sysFlagInner);
                  }

                  PullMessageRequestHeader requestHeader = new PullMessageRequestHeader();
                  requestHeader.setConsumerGroup(this.consumerGroup);
                  requestHeader.setTopic(mq.getTopic());
                  requestHeader.setQueueId(mq.getQueueId());
                  requestHeader.setQueueOffset(offset);
                  requestHeader.setMaxMsgNums(maxNums);
                  requestHeader.setSysFlag(sysFlagInner);
                  requestHeader.setCommitOffset(commitOffset);
                  requestHeader.setSuspendTimeoutMillis(brokerSuspendMaxTimeMillis);
                  requestHeader.setSubscription(subExpression);
                  requestHeader.setSubVersion(subVersion);
                  requestHeader.setExpressionType(expressionType);

                  String brokerAddr = findBrokerResult.getBrokerAddr();
                  if (PullSysFlag.hasClassFilterFlag(sysFlagInner)) {
                      brokerAddr = computPullFromWhichFilterServer(mq.getTopic(), brokerAddr);
                  }

                  PullResult pullResult = this.mQClientFactory.getMQClientAPIImpl().pullMessage(
                      brokerAddr,
                      requestHeader,
                      timeoutMillis,
                      communicationMode,
                      pullCallback);

                  return pullResult;
              }

              throw new MQClientException("The broker[" + mq.getBrokerName() + "] not exist", null);
          }
          -

          再看下一步的

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          public PullResult pullMessage(
              final String addr,
              final PullMessageRequestHeader requestHeader,
              final long timeoutMillis,
              final CommunicationMode communicationMode,
              final PullCallback pullCallback
          ) throws RemotingException, MQBrokerException, InterruptedException {
              RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.PULL_MESSAGE, requestHeader);

              switch (communicationMode) {
                  case ONEWAY:
                      assert false;
                      return null;
                  case ASYNC:
                      this.pullMessageAsync(addr, request, timeoutMillis, pullCallback);
                      return null;
                  case SYNC:
                      return this.pullMessageSync(addr, request, timeoutMillis);
                  default:
                      assert false;
                      break;
              }

              return null;
          }
          -

          通过 communicationMode 判断是同步拉取还是异步拉取，异步就调用

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          private void pullMessageAsync(
                  final String addr,
                  final RemotingCommand request,
                  final long timeoutMillis,
                  final PullCallback pullCallback
              ) throws RemotingException, InterruptedException {
                  this.remotingClient.invokeAsync(addr, request, timeoutMillis, new InvokeCallback() {
                      @Override
                      public void operationComplete(ResponseFuture responseFuture) {
                          异步
                          RemotingCommand response = responseFuture.getResponseCommand();
                          if (response != null) {
                              try {
                                  PullResult pullResult = MQClientAPIImpl.this.processPullResponse(response);
                                  assert pullResult != null;
                                  pullCallback.onSuccess(pullResult);
                              } catch (Exception e) {
                                  pullCallback.onException(e);
                              }
                          } else {
                              if (!responseFuture.isSendRequestOK()) {
                                  pullCallback.onException(new MQClientException("send request failed to " + addr + ". Request: " + request, responseFuture.getCause()));
                              } else if (responseFuture.isTimeout()) {
                                  pullCallback.onException(new MQClientException("wait response from " + addr + " timeout :" + responseFuture.getTimeoutMillis() + "ms" + ". Request: " + request,
                                      responseFuture.getCause()));
                              } else {
                                  pullCallback.onException(new MQClientException("unknown reason. addr: " + addr + ", timeoutMillis: " + timeoutMillis + ". Request: " + request, responseFuture.getCause()));
                              }
                          }
                      }
                  });
              }
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          并且会调用前面 pullCallback 的onSuccess和onException方法，同步的就是调用

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          private PullResult pullMessageSync(
                  final String addr,
                  final RemotingCommand request,
                  final long timeoutMillis
              ) throws RemotingException, InterruptedException, MQBrokerException {
                  RemotingCommand response = this.remotingClient.invokeSync(addr, request, timeoutMillis);
                  assert response != null;
                  return this.processPullResponse(response);
              }
          -

          然后就是这个 remotingClient 的 invokeAsync 跟 invokeSync 方法

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          @Override
              public void invokeAsync(String addr, RemotingCommand request, long timeoutMillis, InvokeCallback invokeCallback)
                  throws InterruptedException, RemotingConnectException, RemotingTooMuchRequestException, RemotingTimeoutException,
                  RemotingSendRequestException {
                  long beginStartTime = System.currentTimeMillis();
                  final Channel channel = this.getAndCreateChannel(addr);
                  if (channel != null && channel.isActive()) {
                      try {
                          doBeforeRpcHooks(addr, request);
                          long costTime = System.currentTimeMillis() - beginStartTime;
                          if (timeoutMillis < costTime) {
                              throw new RemotingTooMuchRequestException("invokeAsync call timeout");
                          }
                          this.invokeAsyncImpl(channel, request, timeoutMillis - costTime, invokeCallback);
                      } catch (RemotingSendRequestException e) {
                          log.warn("invokeAsync: send request exception, so close the channel[{}]", addr);
                          this.closeChannel(addr, channel);
                          throw e;
                      }
                  } else {
                      this.closeChannel(addr, channel);
                      throw new RemotingConnectException(addr);
                  }
              }
          @Override
              public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)
                  throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {
                  long beginStartTime = System.currentTimeMillis();
                  final Channel channel = this.getAndCreateChannel(addr);
                  if (channel != null && channel.isActive()) {
                      try {
                          doBeforeRpcHooks(addr, request);
                          long costTime = System.currentTimeMillis() - beginStartTime;
                          if (timeoutMillis < costTime) {
                              throw new RemotingTimeoutException("invokeSync call timeout");
                          }
                          RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime);
                          doAfterRpcHooks(RemotingHelper.parseChannelRemoteAddr(channel), request, response);
                          return response;
                      } catch (RemotingSendRequestException e) {
                          log.warn("invokeSync: send request exception, so close the channel[{}]", addr);
                          this.closeChannel(addr, channel);
                          throw e;
                      } catch (RemotingTimeoutException e) {
                          if (nettyClientConfig.isClientCloseSocketIfTimeout()) {
                              this.closeChannel(addr, channel);
                              log.warn("invokeSync: close socket because of timeout, {}ms, {}", timeoutMillis, addr);
                          }
                          log.warn("invokeSync: wait response timeout exception, the channel[{}]", addr);
                          throw e;
                      }
                  } else {
                      this.closeChannel(addr, channel);
                      throw new RemotingConnectException(addr);
                  }
              }
          -

          再往下看

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          public RemotingCommand invokeSyncImpl(final Channel channel, final RemotingCommand request,
                  final long timeoutMillis)
                  throws InterruptedException, RemotingSendRequestException, RemotingTimeoutException {
                  final int opaque = request.getOpaque();

                  try {
                      同步跟异步都是会把结果用ResponseFuture抱起来
                      final ResponseFuture responseFuture = new ResponseFuture(channel, opaque, timeoutMillis, null, null);
                      this.responseTable.put(opaque, responseFuture);
                      final SocketAddress addr = channel.remoteAddress();
                      channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
                          @Override
                          public void operationComplete(ChannelFuture f) throws Exception {
                              if (f.isSuccess()) {
                                  responseFuture.setSendRequestOK(true);
                                  return;
                              } else {
                                  responseFuture.setSendRequestOK(false);
                              }

                              responseTable.remove(opaque);
                              responseFuture.setCause(f.cause());
                              responseFuture.putResponse(null);
                              log.warn("send a request command to channel <" + addr + "> failed.");
                          }
                      });
                      // 区别是同步的是在这等待
                      RemotingCommand responseCommand = responseFuture.waitResponse(timeoutMillis);
                      if (null == responseCommand) {
                          if (responseFuture.isSendRequestOK()) {
                              throw new RemotingTimeoutException(RemotingHelper.parseSocketAddressAddr(addr), timeoutMillis,
                                  responseFuture.getCause());
                          } else {
                              throw new RemotingSendRequestException(RemotingHelper.parseSocketAddressAddr(addr), responseFuture.getCause());
                          }
                      }

                      return responseCommand;
                  } finally {
                      this.responseTable.remove(opaque);
                  }
              }

              public void invokeAsyncImpl(final Channel channel, final RemotingCommand request, final long timeoutMillis,
                  final InvokeCallback invokeCallback)
                  throws InterruptedException, RemotingTooMuchRequestException, RemotingTimeoutException, RemotingSendRequestException {
                  long beginStartTime = System.currentTimeMillis();
                  final int opaque = request.getOpaque();
                  boolean acquired = this.semaphoreAsync.tryAcquire(timeoutMillis, TimeUnit.MILLISECONDS);
                  if (acquired) {
                      final SemaphoreReleaseOnlyOnce once = new SemaphoreReleaseOnlyOnce(this.semaphoreAsync);
                      long costTime = System.currentTimeMillis() - beginStartTime;
                      if (timeoutMillis < costTime) {
                          once.release();
                          throw new RemotingTimeoutException("invokeAsyncImpl call timeout");
                      }

                      final ResponseFuture responseFuture = new ResponseFuture(channel, opaque, timeoutMillis - costTime, invokeCallback, once);
                      this.responseTable.put(opaque, responseFuture);
                      try {
                          channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
                              @Override
                              public void operationComplete(ChannelFuture f) throws Exception {
                                  if (f.isSuccess()) {
                                      responseFuture.setSendRequestOK(true);
                                      return;
                                  }
                                  requestFail(opaque);
                                  log.warn("send a request command to channel <{}> failed.", RemotingHelper.parseChannelRemoteAddr(channel));
                              }
                          });
                      } catch (Exception e) {
                          responseFuture.release();
                          log.warn("send a request command to channel <" + RemotingHelper.parseChannelRemoteAddr(channel) + "> Exception", e);
                          throw new RemotingSendRequestException(RemotingHelper.parseChannelRemoteAddr(channel), e);
                      }
                  } else {
                      if (timeoutMillis <= 0) {
                          throw new RemotingTooMuchRequestException("invokeAsyncImpl invoke too fast");
                      } else {
                          String info =
                              String.format("invokeAsyncImpl tryAcquire semaphore timeout, %dms, waiting thread nums: %d semaphoreAsyncValue: %d",
                                  timeoutMillis,
                                  this.semaphoreAsync.getQueueLength(),
                                  this.semaphoreAsync.availablePermits()
                              );
                          log.warn(info);
                          throw new RemotingTimeoutException(info);
                      }
                  }
              }
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          - - - - @@ -944,20 +912,20 @@
          - 70 + 71 posts
          - 81 + 83 categories
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          @@ -982,7 +950,7 @@
          - +
          diff --git a/page/4/index.html b/page/4/index.html index e0fa4f263a..8eb211c255 100644 --- a/page/4/index.html +++ b/page/4/index.html @@ -203,6 +203,154 @@ +
          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + Edited on + + + + + + + In + + + + , + + + + , + + + + , + + + + , + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          首先看下官方的小 demo

          +
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          public static void main(String[] args) throws InterruptedException, MQClientException {

                  /*
                   * Instantiate with specified consumer group name.
                   * 首先是new 一个对象出来，然后指定 Consumer 的 Group
                   * 同一类Consumer的集合，这类Consumer通常消费同一类消息且消费逻辑一致。消费者组使得在消息消费方面，实现负载均衡和容错的目标变得非常容易。要注意的是，消费者组的消费者实例必须订阅完全相同的Topic。RocketMQ 支持两种消息模式：集群消费（Clustering）和广播消费（Broadcasting）。
                   */
                  DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name_4");

                  /*
                   * Specify name server addresses.
                   * <p/>
                   * 这里可以通知指定环境变量或者设置对象参数的形式指定名字空间服务的地址
                   *
                   * Alternatively, you may specify name server addresses via exporting environmental variable: NAMESRV_ADDR
                   * <pre>
                   * {@code
                   * consumer.setNamesrvAddr("name-server1-ip:9876;name-server2-ip:9876");
                   * }
                   * </pre>
                   */

                  /*
                   * Specify where to start in case the specified consumer group is a brand new one.
                   * 指定消费起始点
                   */
                  consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);

                  /*
                   * Subscribe one more more topics to consume.
                   * 指定订阅的 topic 跟 tag，注意后面的是个表达式，可以以 tag1 || tag2 || tag3 传入
                   */
                  consumer.subscribe("TopicTest", "*");

                  /*
                   *  Register callback to execute on arrival of messages fetched from brokers.
                   *  注册具体获得消息后的处理方法
                   */
                  consumer.registerMessageListener(new MessageListenerConcurrently() {

                      @Override
                      public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs,
                          ConsumeConcurrentlyContext context) {
                          System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
                          return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
                      }
                  });

                  /*
                   *  Launch the consumer instance.
                   * 启动消费者
                   */
                  consumer.start();

                  System.out.printf("Consumer Started.%n");
              }
          + +

          然后就是看看 start 的过程了

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          /**
               * This method gets internal infrastructure readily to serve. Instances must call this method after configuration.
               *
               * @throws MQClientException if there is any client error.
               */
              @Override
              public void start() throws MQClientException {
                  setConsumerGroup(NamespaceUtil.wrapNamespace(this.getNamespace(), this.consumerGroup));
                  this.defaultMQPushConsumerImpl.start();
                  if (null != traceDispatcher) {
                      try {
                          traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
                      } catch (MQClientException e) {
                          log.warn("trace dispatcher start failed ", e);
                      }
                  }
              }
          +

          具体的逻辑在this.defaultMQPushConsumerImpl.start()，这个 defaultMQPushConsumerImpl 就是

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          /**
               * Internal implementation. Most of the functions herein are delegated to it.
               */
              protected final transient DefaultMQPushConsumerImpl defaultMQPushConsumerImpl;
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          public synchronized void start() throws MQClientException {
                  switch (this.serviceState) {
                      case CREATE_JUST:
                          log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),
                              this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());
                          // 这里比较巧妙，相当于想设立了个屏障，防止并发启动，不过这里并不是悲观锁，也不算个严格的乐观锁
                          this.serviceState = ServiceState.START_FAILED;

                          this.checkConfig();

                          this.copySubscription();

                          if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
                              this.defaultMQPushConsumer.changeInstanceNameToPID();
                          }

                          // 这个mQClientFactory，负责管理client（consumer、producer），并提供多中功能接口供各个Service（Rebalance、PullMessage等）调用；大部分逻辑均在这个类中完成
                          this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);

                          // 这个 rebalanceImpl 主要负责决定，当前的consumer应该从哪些Queue中消费消息；
                          this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
                          this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
                          this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
                          this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);

                          // 长连接，负责从broker处拉取消息，然后利用ConsumeMessageService回调用户的Listener执行消息消费逻辑
                          this.pullAPIWrapper = new PullAPIWrapper(
                              mQClientFactory,
                              this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
                          this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);

                          if (this.defaultMQPushConsumer.getOffsetStore() != null) {
                              this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
                          } else {
                              switch (this.defaultMQPushConsumer.getMessageModel()) {
                                  case BROADCASTING:
                                      this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
                                      break;
                                  case CLUSTERING:
                                      this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
                                      break;
                                  default:
                                      break;
                              }
                              this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);
                          }
                          // offsetStore 维护当前consumer的消费记录（offset）；有两种实现，Local和Rmote，Local存储在本地磁盘上，适用于BROADCASTING广播消费模式；而Remote则将消费进度存储在Broker上，适用于CLUSTERING集群消费模式；
                          this.offsetStore.load();

                          if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
                              this.consumeOrderly = true;
                              this.consumeMessageService =
                                  new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
                          } else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
                              this.consumeOrderly = false;
                              this.consumeMessageService =
                                  new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
                          }

                          // 实现所谓的"Push-被动"消费机制；从Broker拉取的消息后，封装成ConsumeRequest提交给ConsumeMessageSerivce，此service负责回调用户的Listener消费消息；
                          this.consumeMessageService.start();

                          boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
                          if (!registerOK) {
                              this.serviceState = ServiceState.CREATE_JUST;
                              this.consumeMessageService.shutdown();
                              throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()
                                  + "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
                                  null);
                          }

                          mQClientFactory.start();
                          log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());
                          this.serviceState = ServiceState.RUNNING;
                          break;
                      case RUNNING:
                      case START_FAILED:
                      case SHUTDOWN_ALREADY:
                          throw new MQClientException("The PushConsumer service state not OK, maybe started once, "
                              + this.serviceState
                              + FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
                              null);
                      default:
                          break;
                  }

                  this.updateTopicSubscribeInfoWhenSubscriptionChanged();
                  this.mQClientFactory.checkClientInBroker();
                  this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
                  this.mQClientFactory.rebalanceImmediately();
              }
          +

          然后我们往下看主要的目光聚焦mQClientFactory.start()

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          public void start() throws MQClientException {

                  synchronized (this) {
                      switch (this.serviceState) {
                          case CREATE_JUST:
                              this.serviceState = ServiceState.START_FAILED;
                              // If not specified,looking address from name server
                              if (null == this.clientConfig.getNamesrvAddr()) {
                                  this.mQClientAPIImpl.fetchNameServerAddr();
                              }
                              // Start request-response channel
                              // 这里主要是初始化了个网络客户端
                              this.mQClientAPIImpl.start();
                              // Start various schedule tasks
                              // 定时任务
                              this.startScheduledTask();
                              // Start pull service
                              // 这里重点说下
                              this.pullMessageService.start();
                              // Start rebalance service
                              this.rebalanceService.start();
                              // Start push service
                              this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
                              log.info("the client factory [{}] start OK", this.clientId);
                              this.serviceState = ServiceState.RUNNING;
                              break;
                          case START_FAILED:
                              throw new MQClientException("The Factory object[" + this.getClientId() + "] has been created before, and failed.", null);
                          default:
                              break;
                      }
                  }
              }
          +

          我们来看下这个 pullMessageService，org.apache.rocketmq.client.impl.consumer.PullMessageService，

          实现了 runnable 接口，
          然后可以看到 run 方法

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          public void run() {
                  log.info(this.getServiceName() + " service started");

                  while (!this.isStopped()) {
                      try {
                          PullRequest pullRequest = this.pullRequestQueue.take();
                          this.pullMessage(pullRequest);
                      } catch (InterruptedException ignored) {
                      } catch (Exception e) {
                          log.error("Pull Message Service Run Method exception", e);
                      }
                  }

                  log.info(this.getServiceName() + " service end");
              }
          +

          接着在看 pullMessage 方法

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          private void pullMessage(final PullRequest pullRequest) {
                  final MQConsumerInner consumer = this.mQClientFactory.selectConsumer(pullRequest.getConsumerGroup());
                  if (consumer != null) {
                      DefaultMQPushConsumerImpl impl = (DefaultMQPushConsumerImpl) consumer;
                      impl.pullMessage(pullRequest);
                  } else {
                      log.warn("No matched consumer for the PullRequest {}, drop it", pullRequest);
                  }
              }
          +

          实际上调用了这个方法，这个方法很长，我在代码里注释下下每一段的功能

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          public void pullMessage(final PullRequest pullRequest) {
                  final ProcessQueue processQueue = pullRequest.getProcessQueue();
                  // 这里开始就是检查状态，确定是否往下执行
                  if (processQueue.isDropped()) {
                      log.info("the pull request[{}] is dropped.", pullRequest.toString());
                      return;
                  }

                  pullRequest.getProcessQueue().setLastPullTimestamp(System.currentTimeMillis());

                  try {
                      this.makeSureStateOK();
                  } catch (MQClientException e) {
                      log.warn("pullMessage exception, consumer state not ok", e);
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      return;
                  }

                  if (this.isPause()) {
                      log.warn("consumer was paused, execute pull request later. instanceName={}, group={}", this.defaultMQPushConsumer.getInstanceName(), this.defaultMQPushConsumer.getConsumerGroup());
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_SUSPEND);
                      return;
                  }

                  // 这块其实是个类似于限流的功能块，对消息数量和消息大小做限制
                  long cachedMessageCount = processQueue.getMsgCount().get();
                  long cachedMessageSizeInMiB = processQueue.getMsgSize().get() / (1024 * 1024);

                  if (cachedMessageCount > this.defaultMQPushConsumer.getPullThresholdForQueue()) {
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                      if ((queueFlowControlTimes++ % 1000) == 0) {
                          log.warn(
                              "the cached message count exceeds the threshold {}, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
                              this.defaultMQPushConsumer.getPullThresholdForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
                      }
                      return;
                  }

                  if (cachedMessageSizeInMiB > this.defaultMQPushConsumer.getPullThresholdSizeForQueue()) {
                      this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                      if ((queueFlowControlTimes++ % 1000) == 0) {
                          log.warn(
                              "the cached message size exceeds the threshold {} MiB, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
                              this.defaultMQPushConsumer.getPullThresholdSizeForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
                      }
                      return;
                  }

                  // 若不是顺序消费（即DefaultMQPushConsumerImpl.consumeOrderly等于false），则检查ProcessQueue对象的msgTreeMap:TreeMap<Long,MessageExt>变量的第一个key值与最后一个key值之间的差额，该key值表示查询的队列偏移量queueoffset；若差额大于阈值（由DefaultMQPushConsumer. consumeConcurrentlyMaxSpan指定，默认是2000），则调用PullMessageService.executePullRequestLater方法，在50毫秒之后重新将该PullRequest请求放入PullMessageService.pullRequestQueue队列中；并跳出该方法；这里的意思主要就是消息有堆积了，等会再来拉取
                  if (!this.consumeOrderly) {
                      if (processQueue.getMaxSpan() > this.defaultMQPushConsumer.getConsumeConcurrentlyMaxSpan()) {
                          this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
                          if ((queueMaxSpanFlowControlTimes++ % 1000) == 0) {
                              log.warn(
                                  "the queue's messages, span too long, so do flow control, minOffset={}, maxOffset={}, maxSpan={}, pullRequest={}, flowControlTimes={}",
                                  processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), processQueue.getMaxSpan(),
                                  pullRequest, queueMaxSpanFlowControlTimes);
                          }
                          return;
                      }
                  } else {
                      if (processQueue.isLocked()) {
                          if (!pullRequest.isLockedFirst()) {
                              final long offset = this.rebalanceImpl.computePullFromWhere(pullRequest.getMessageQueue());
                              boolean brokerBusy = offset < pullRequest.getNextOffset();
                              log.info("the first time to pull message, so fix offset from broker. pullRequest: {} NewOffset: {} brokerBusy: {}",
                                  pullRequest, offset, brokerBusy);
                              if (brokerBusy) {
                                  log.info("[NOTIFYME]the first time to pull message, but pull request offset larger than broker consume offset. pullRequest: {} NewOffset: {}",
                                      pullRequest, offset);
                              }

                              pullRequest.setLockedFirst(true);
                              pullRequest.setNextOffset(offset);
                          }
                      } else {
                          this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                          log.info("pull message later because not locked in broker, {}", pullRequest);
                          return;
                      }
                  }

                  // 以PullRequest.messageQueue对象的topic值为参数从RebalanceImpl.subscriptionInner: ConcurrentHashMap, SubscriptionData>中获取对应的SubscriptionData对象，若该对象为null，考虑到并发的关系，调用executePullRequestLater方法，稍后重试；并跳出该方法；
                  final SubscriptionData subscriptionData = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
                  if (null == subscriptionData) {
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      log.warn("find the consumer's subscription failed, {}", pullRequest);
                      return;
                  }

                  final long beginTimestamp = System.currentTimeMillis();

                  // 异步拉取回调，先不讨论细节
                  PullCallback pullCallback = new PullCallback() {
                      @Override
                      public void onSuccess(PullResult pullResult) {
                          if (pullResult != null) {
                              pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult,
                                  subscriptionData);

                              switch (pullResult.getPullStatus()) {
                                  case FOUND:
                                      long prevRequestOffset = pullRequest.getNextOffset();
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());
                                      long pullRT = System.currentTimeMillis() - beginTimestamp;
                                      DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullRT(pullRequest.getConsumerGroup(),
                                          pullRequest.getMessageQueue().getTopic(), pullRT);

                                      long firstMsgOffset = Long.MAX_VALUE;
                                      if (pullResult.getMsgFoundList() == null || pullResult.getMsgFoundList().isEmpty()) {
                                          DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      } else {
                                          firstMsgOffset = pullResult.getMsgFoundList().get(0).getQueueOffset();

                                          DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullTPS(pullRequest.getConsumerGroup(),
                                              pullRequest.getMessageQueue().getTopic(), pullResult.getMsgFoundList().size());

                                          boolean dispatchToConsume = processQueue.putMessage(pullResult.getMsgFoundList());
                                          DefaultMQPushConsumerImpl.this.consumeMessageService.submitConsumeRequest(
                                              pullResult.getMsgFoundList(),
                                              processQueue,
                                              pullRequest.getMessageQueue(),
                                              dispatchToConsume);

                                          if (DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval() > 0) {
                                              DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest,
                                                  DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval());
                                          } else {
                                              DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                          }
                                      }

                                      if (pullResult.getNextBeginOffset() < prevRequestOffset
                                          || firstMsgOffset < prevRequestOffset) {
                                          log.warn(
                                              "[BUG] pull message result maybe data wrong, nextBeginOffset: {} firstMsgOffset: {} prevRequestOffset: {}",
                                              pullResult.getNextBeginOffset(),
                                              firstMsgOffset,
                                              prevRequestOffset);
                                      }

                                      break;
                                  case NO_NEW_MSG:
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);

                                      DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      break;
                                  case NO_MATCHED_MSG:
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);

                                      DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
                                      break;
                                  case OFFSET_ILLEGAL:
                                      log.warn("the pull request offset illegal, {} {}",
                                          pullRequest.toString(), pullResult.toString());
                                      pullRequest.setNextOffset(pullResult.getNextBeginOffset());

                                      pullRequest.getProcessQueue().setDropped(true);
                                      DefaultMQPushConsumerImpl.this.executeTaskLater(new Runnable() {

                                          @Override
                                          public void run() {
                                              try {
                                                  DefaultMQPushConsumerImpl.this.offsetStore.updateOffset(pullRequest.getMessageQueue(),
                                                      pullRequest.getNextOffset(), false);

                                                  DefaultMQPushConsumerImpl.this.offsetStore.persist(pullRequest.getMessageQueue());

                                                  DefaultMQPushConsumerImpl.this.rebalanceImpl.removeProcessQueue(pullRequest.getMessageQueue());

                                                  log.warn("fix the pull request offset, {}", pullRequest);
                                              } catch (Throwable e) {
                                                  log.error("executeTaskLater Exception", e);
                                              }
                                          }
                                      }, 10000);
                                      break;
                                  default:
                                      break;
                              }
                          }
                      }

                      @Override
                      public void onException(Throwable e) {
                          if (!pullRequest.getMessageQueue().getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
                              log.warn("execute the pull request exception", e);
                          }

                          DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                      }
                  };
                  // 如果为集群模式，即可置commitOffsetEnable为 true
                  boolean commitOffsetEnable = false;
                  long commitOffsetValue = 0L;
                  if (MessageModel.CLUSTERING == this.defaultMQPushConsumer.getMessageModel()) {
                      commitOffsetValue = this.offsetStore.readOffset(pullRequest.getMessageQueue(), ReadOffsetType.READ_FROM_MEMORY);
                      if (commitOffsetValue > 0) {
                          commitOffsetEnable = true;
                      }
                  }

                  // 将上面获得的commitOffsetEnable更新到订阅关系里
                  String subExpression = null;
                  boolean classFilter = false;
                  SubscriptionData sd = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
                  if (sd != null) {
                      if (this.defaultMQPushConsumer.isPostSubscriptionWhenPull() && !sd.isClassFilterMode()) {
                          subExpression = sd.getSubString();
                      }

                      classFilter = sd.isClassFilterMode();
                  }

                  // 组成 sysFlag
                  int sysFlag = PullSysFlag.buildSysFlag(
                      commitOffsetEnable, // commitOffset
                      true, // suspend
                      subExpression != null, // subscription
                      classFilter // class filter
                  );
                  // 调用真正的拉取消息接口
                  try {
                      this.pullAPIWrapper.pullKernelImpl(
                          pullRequest.getMessageQueue(),
                          subExpression,
                          subscriptionData.getExpressionType(),
                          subscriptionData.getSubVersion(),
                          pullRequest.getNextOffset(),
                          this.defaultMQPushConsumer.getPullBatchSize(),
                          sysFlag,
                          commitOffsetValue,
                          BROKER_SUSPEND_MAX_TIME_MILLIS,
                          CONSUMER_TIMEOUT_MILLIS_WHEN_SUSPEND,
                          CommunicationMode.ASYNC,
                          pullCallback
                      );
                  } catch (Exception e) {
                      log.error("pullKernelImpl exception", e);
                      this.executePullRequestLater(pullRequest, pullTimeDelayMillsWhenException);
                  }
              }
          +

          以下就是拉取消息的底层 api，不够不是特别复杂，主要是在找 broker，和设置请求参数

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          public PullResult pullKernelImpl(
              final MessageQueue mq,
              final String subExpression,
              final String expressionType,
              final long subVersion,
              final long offset,
              final int maxNums,
              final int sysFlag,
              final long commitOffset,
              final long brokerSuspendMaxTimeMillis,
              final long timeoutMillis,
              final CommunicationMode communicationMode,
              final PullCallback pullCallback
          ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
              FindBrokerResult findBrokerResult =
                  this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                      this.recalculatePullFromWhichNode(mq), false);
              if (null == findBrokerResult) {
                  this.mQClientFactory.updateTopicRouteInfoFromNameServer(mq.getTopic());
                  findBrokerResult =
                      this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                          this.recalculatePullFromWhichNode(mq), false);
              }

              if (findBrokerResult != null) {
                  {
                      // check version
                      if (!ExpressionType.isTagType(expressionType)
                          && findBrokerResult.getBrokerVersion() < MQVersion.Version.V4_1_0_SNAPSHOT.ordinal()) {
                          throw new MQClientException("The broker[" + mq.getBrokerName() + ", "
                              + findBrokerResult.getBrokerVersion() + "] does not upgrade to support for filter message by " + expressionType, null);
                      }
                  }
                  int sysFlagInner = sysFlag;

                  if (findBrokerResult.isSlave()) {
                      sysFlagInner = PullSysFlag.clearCommitOffsetFlag(sysFlagInner);
                  }

                  PullMessageRequestHeader requestHeader = new PullMessageRequestHeader();
                  requestHeader.setConsumerGroup(this.consumerGroup);
                  requestHeader.setTopic(mq.getTopic());
                  requestHeader.setQueueId(mq.getQueueId());
                  requestHeader.setQueueOffset(offset);
                  requestHeader.setMaxMsgNums(maxNums);
                  requestHeader.setSysFlag(sysFlagInner);
                  requestHeader.setCommitOffset(commitOffset);
                  requestHeader.setSuspendTimeoutMillis(brokerSuspendMaxTimeMillis);
                  requestHeader.setSubscription(subExpression);
                  requestHeader.setSubVersion(subVersion);
                  requestHeader.setExpressionType(expressionType);

                  String brokerAddr = findBrokerResult.getBrokerAddr();
                  if (PullSysFlag.hasClassFilterFlag(sysFlagInner)) {
                      brokerAddr = computPullFromWhichFilterServer(mq.getTopic(), brokerAddr);
                  }

                  PullResult pullResult = this.mQClientFactory.getMQClientAPIImpl().pullMessage(
                      brokerAddr,
                      requestHeader,
                      timeoutMillis,
                      communicationMode,
                      pullCallback);

                  return pullResult;
              }

              throw new MQClientException("The broker[" + mq.getBrokerName() + "] not exist", null);
          }
          +

          再看下一步的

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          public PullResult pullMessage(
              final String addr,
              final PullMessageRequestHeader requestHeader,
              final long timeoutMillis,
              final CommunicationMode communicationMode,
              final PullCallback pullCallback
          ) throws RemotingException, MQBrokerException, InterruptedException {
              RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.PULL_MESSAGE, requestHeader);

              switch (communicationMode) {
                  case ONEWAY:
                      assert false;
                      return null;
                  case ASYNC:
                      this.pullMessageAsync(addr, request, timeoutMillis, pullCallback);
                      return null;
                  case SYNC:
                      return this.pullMessageSync(addr, request, timeoutMillis);
                  default:
                      assert false;
                      break;
              }

              return null;
          }
          +

          通过 communicationMode 判断是同步拉取还是异步拉取，异步就调用

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          private void pullMessageAsync(
                  final String addr,
                  final RemotingCommand request,
                  final long timeoutMillis,
                  final PullCallback pullCallback
              ) throws RemotingException, InterruptedException {
                  this.remotingClient.invokeAsync(addr, request, timeoutMillis, new InvokeCallback() {
                      @Override
                      public void operationComplete(ResponseFuture responseFuture) {
                          异步
                          RemotingCommand response = responseFuture.getResponseCommand();
                          if (response != null) {
                              try {
                                  PullResult pullResult = MQClientAPIImpl.this.processPullResponse(response);
                                  assert pullResult != null;
                                  pullCallback.onSuccess(pullResult);
                              } catch (Exception e) {
                                  pullCallback.onException(e);
                              }
                          } else {
                              if (!responseFuture.isSendRequestOK()) {
                                  pullCallback.onException(new MQClientException("send request failed to " + addr + ". Request: " + request, responseFuture.getCause()));
                              } else if (responseFuture.isTimeout()) {
                                  pullCallback.onException(new MQClientException("wait response from " + addr + " timeout :" + responseFuture.getTimeoutMillis() + "ms" + ". Request: " + request,
                                      responseFuture.getCause()));
                              } else {
                                  pullCallback.onException(new MQClientException("unknown reason. addr: " + addr + ", timeoutMillis: " + timeoutMillis + ". Request: " + request, responseFuture.getCause()));
                              }
                          }
                      }
                  });
              }
          +

          并且会调用前面 pullCallback 的onSuccess和onException方法，同步的就是调用

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          private PullResult pullMessageSync(
                  final String addr,
                  final RemotingCommand request,
                  final long timeoutMillis
              ) throws RemotingException, InterruptedException, MQBrokerException {
                  RemotingCommand response = this.remotingClient.invokeSync(addr, request, timeoutMillis);
                  assert response != null;
                  return this.processPullResponse(response);
              }
          +

          然后就是这个 remotingClient 的 invokeAsync 跟 invokeSync 方法

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          @Override
              public void invokeAsync(String addr, RemotingCommand request, long timeoutMillis, InvokeCallback invokeCallback)
                  throws InterruptedException, RemotingConnectException, RemotingTooMuchRequestException, RemotingTimeoutException,
                  RemotingSendRequestException {
                  long beginStartTime = System.currentTimeMillis();
                  final Channel channel = this.getAndCreateChannel(addr);
                  if (channel != null && channel.isActive()) {
                      try {
                          doBeforeRpcHooks(addr, request);
                          long costTime = System.currentTimeMillis() - beginStartTime;
                          if (timeoutMillis < costTime) {
                              throw new RemotingTooMuchRequestException("invokeAsync call timeout");
                          }
                          this.invokeAsyncImpl(channel, request, timeoutMillis - costTime, invokeCallback);
                      } catch (RemotingSendRequestException e) {
                          log.warn("invokeAsync: send request exception, so close the channel[{}]", addr);
                          this.closeChannel(addr, channel);
                          throw e;
                      }
                  } else {
                      this.closeChannel(addr, channel);
                      throw new RemotingConnectException(addr);
                  }
              }
          @Override
              public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)
                  throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {
                  long beginStartTime = System.currentTimeMillis();
                  final Channel channel = this.getAndCreateChannel(addr);
                  if (channel != null && channel.isActive()) {
                      try {
                          doBeforeRpcHooks(addr, request);
                          long costTime = System.currentTimeMillis() - beginStartTime;
                          if (timeoutMillis < costTime) {
                              throw new RemotingTimeoutException("invokeSync call timeout");
                          }
                          RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime);
                          doAfterRpcHooks(RemotingHelper.parseChannelRemoteAddr(channel), request, response);
                          return response;
                      } catch (RemotingSendRequestException e) {
                          log.warn("invokeSync: send request exception, so close the channel[{}]", addr);
                          this.closeChannel(addr, channel);
                          throw e;
                      } catch (RemotingTimeoutException e) {
                          if (nettyClientConfig.isClientCloseSocketIfTimeout()) {
                              this.closeChannel(addr, channel);
                              log.warn("invokeSync: close socket because of timeout, {}ms, {}", timeoutMillis, addr);
                          }
                          log.warn("invokeSync: wait response timeout exception, the channel[{}]", addr);
                          throw e;
                      }
                  } else {
                      this.closeChannel(addr, channel);
                      throw new RemotingConnectException(addr);
                  }
              }
          +

          再往下看

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          public RemotingCommand invokeSyncImpl(final Channel channel, final RemotingCommand request,
                  final long timeoutMillis)
                  throws InterruptedException, RemotingSendRequestException, RemotingTimeoutException {
                  final int opaque = request.getOpaque();

                  try {
                      同步跟异步都是会把结果用ResponseFuture抱起来
                      final ResponseFuture responseFuture = new ResponseFuture(channel, opaque, timeoutMillis, null, null);
                      this.responseTable.put(opaque, responseFuture);
                      final SocketAddress addr = channel.remoteAddress();
                      channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
                          @Override
                          public void operationComplete(ChannelFuture f) throws Exception {
                              if (f.isSuccess()) {
                                  responseFuture.setSendRequestOK(true);
                                  return;
                              } else {
                                  responseFuture.setSendRequestOK(false);
                              }

                              responseTable.remove(opaque);
                              responseFuture.setCause(f.cause());
                              responseFuture.putResponse(null);
                              log.warn("send a request command to channel <" + addr + "> failed.");
                          }
                      });
                      // 区别是同步的是在这等待
                      RemotingCommand responseCommand = responseFuture.waitResponse(timeoutMillis);
                      if (null == responseCommand) {
                          if (responseFuture.isSendRequestOK()) {
                              throw new RemotingTimeoutException(RemotingHelper.parseSocketAddressAddr(addr), timeoutMillis,
                                  responseFuture.getCause());
                          } else {
                              throw new RemotingSendRequestException(RemotingHelper.parseSocketAddressAddr(addr), responseFuture.getCause());
                          }
                      }

                      return responseCommand;
                  } finally {
                      this.responseTable.remove(opaque);
                  }
              }

              public void invokeAsyncImpl(final Channel channel, final RemotingCommand request, final long timeoutMillis,
                  final InvokeCallback invokeCallback)
                  throws InterruptedException, RemotingTooMuchRequestException, RemotingTimeoutException, RemotingSendRequestException {
                  long beginStartTime = System.currentTimeMillis();
                  final int opaque = request.getOpaque();
                  boolean acquired = this.semaphoreAsync.tryAcquire(timeoutMillis, TimeUnit.MILLISECONDS);
                  if (acquired) {
                      final SemaphoreReleaseOnlyOnce once = new SemaphoreReleaseOnlyOnce(this.semaphoreAsync);
                      long costTime = System.currentTimeMillis() - beginStartTime;
                      if (timeoutMillis < costTime) {
                          once.release();
                          throw new RemotingTimeoutException("invokeAsyncImpl call timeout");
                      }

                      final ResponseFuture responseFuture = new ResponseFuture(channel, opaque, timeoutMillis - costTime, invokeCallback, once);
                      this.responseTable.put(opaque, responseFuture);
                      try {
                          channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
                              @Override
                              public void operationComplete(ChannelFuture f) throws Exception {
                                  if (f.isSuccess()) {
                                      responseFuture.setSendRequestOK(true);
                                      return;
                                  }
                                  requestFail(opaque);
                                  log.warn("send a request command to channel <{}> failed.", RemotingHelper.parseChannelRemoteAddr(channel));
                              }
                          });
                      } catch (Exception e) {
                          responseFuture.release();
                          log.warn("send a request command to channel <" + RemotingHelper.parseChannelRemoteAddr(channel) + "> Exception", e);
                          throw new RemotingSendRequestException(RemotingHelper.parseChannelRemoteAddr(channel), e);
                      }
                  } else {
                      if (timeoutMillis <= 0) {
                          throw new RemotingTooMuchRequestException("invokeAsyncImpl invoke too fast");
                      } else {
                          String info =
                              String.format("invokeAsyncImpl tryAcquire semaphore timeout, %dms, waiting thread nums: %d semaphoreAsyncValue: %d",
                                  timeoutMillis,
                                  this.semaphoreAsync.getQueueLength(),
                                  this.semaphoreAsync.availablePermits()
                              );
                          log.warn(info);
                          throw new RemotingTimeoutException(info);
                      }
                  }
              }
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          - - - - - -
          -

          - - -

          - -
          - - - - - Posted on - - - - - - - - Edited on - - - - - - - In - - - - , - - - - , - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
          -
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          因为传说中的出身问题，我以前写的是PHP，在使用 swoole 之前，基本的应用调试手段就是简单粗暴的 var_dump，exit，对于单进程模型的 PHP 也是简单有效，技术栈换成 Java 之后，就变得没那么容易，一方面是需要编译，另一方面是一般都是基于 spring 的项目，如果问题定位比较模糊，那框架层的是很难靠简单的 System.out.println 或者打 log 解决，(PS：我觉得可能我写的东西比较适合从 PHP 这种弱类型语言转到 Java 的小白同学)这个时候一方面因为是 Java，有了非常好用的 idea IDE 的支持，可以各种花式调试，条件断点尤其牛叉，但是又因为有 Spring+Java 的双重原因，有些情况下单步调试可以把手按废掉，这也是我之前一直比较困惑苦逼的点，后来随着慢慢精（jiang）进（you）之后，比如对于一个 oom 的情况，我们可以通过启动参数加上-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=xx/xx 来配置溢出时的堆dump 日志，获取到这个文件后，我们可以通过像 Memory Analyzer (MAT)[https://www.eclipse.org/mat/] (The Eclipse Memory Analyzer is a fast and feature-rich Java heap analyzer that helps you find memory leaks and reduce memory consumption.)来查看诊断问题所在，之前用到的时候是因为有个死循环一直往链表里塞数据，属于比较简单的，后来一次是由于运维进行应用迁移时按默认的统一配置了堆内存大小，导致内存的确不够用，所以溢出了，
          今天想说的其实主要是我们的 thread dump，这也是我最近才真正用的一个方法，可能真的很小白了，用过 ide 的单步调试其实都知道会有一个一层层的玩意，比如函数从 A，调用了 B，再从 B 调用了 C，一直往下(因为是 Java，所以还有很多🤦‍♂️)，这个其实也是大部分语言的调用模型，利用了栈这个数据结构，通过这个结构我们可以知道代码的调用链路，由于对于一个 spring 应用，在本身框架代码量非常庞大的情况下，外加如果应用代码也是非常多的时候，有时候通过单步调试真的很难短时间定位到问题，需要非常大的耐心和仔细观察，当然不是说完全不行，举个例子当我的应用经常启动需要非常长的时间，因为本身应用有非常多个 bean，比较难说究竟是 bean 的加载的确很慢还是有什么异常原因，这种时候就可以使用 thread dump 了，具体怎么操作呢

          如果在idea 中运行或者调试时，可以直接点击这个照相机一样的按钮，右边就会出现了左边会显示所有的线程，右边会显示线程栈，

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          "main@1" prio=5 tid=0x1 nid=NA runnable
            java.lang.Thread.State: RUNNABLE
          	  at TreeDistance.treeDist(TreeDistance.java:64)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.main(TreeDistance.java:45)
          -

          这就是我们主线程的堆栈信息了，main 表示这个线程名，prio表示优先级，默认是 5，tid 表示线程 id，nid 表示对应的系统线程，后面的runnable 表示目前线程状态，因为是被我打了断点，所以是就许状态，然后下面就是对应的线程栈内容了，在TreeDistance类的 treeDist方法中，对应的文件行数是 64 行。
          这里使用 thread dump一般也不会是上面我截图代码里的这种代码量很少的，一般是大型项目，有时候跑着跑着没反应，又不知道跑到哪了，特别是一些刚接触的大项目或者需要定位一个大项目的一个疑难问题，一时没思路时，可以使用这个方法，个人觉得非常有帮助。

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          - - - - @@ -899,20 +936,20 @@
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          - +
          diff --git a/page/5/index.html b/page/5/index.html index 7fa093a26f..fe870498c3 100644 --- a/page/5/index.html +++ b/page/5/index.html @@ -203,6 +203,117 @@ +
          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + Edited on + + + + + + + In + + + + , + + + + , + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          因为传说中的出身问题，我以前写的是PHP，在使用 swoole 之前，基本的应用调试手段就是简单粗暴的 var_dump，exit，对于单进程模型的 PHP 也是简单有效，技术栈换成 Java 之后，就变得没那么容易，一方面是需要编译，另一方面是一般都是基于 spring 的项目，如果问题定位比较模糊，那框架层的是很难靠简单的 System.out.println 或者打 log 解决，(PS：我觉得可能我写的东西比较适合从 PHP 这种弱类型语言转到 Java 的小白同学)这个时候一方面因为是 Java，有了非常好用的 idea IDE 的支持，可以各种花式调试，条件断点尤其牛叉，但是又因为有 Spring+Java 的双重原因，有些情况下单步调试可以把手按废掉，这也是我之前一直比较困惑苦逼的点，后来随着慢慢精（jiang）进（you）之后，比如对于一个 oom 的情况，我们可以通过启动参数加上-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=xx/xx 来配置溢出时的堆dump 日志，获取到这个文件后，我们可以通过像 Memory Analyzer (MAT)[https://www.eclipse.org/mat/] (The Eclipse Memory Analyzer is a fast and feature-rich Java heap analyzer that helps you find memory leaks and reduce memory consumption.)来查看诊断问题所在，之前用到的时候是因为有个死循环一直往链表里塞数据，属于比较简单的，后来一次是由于运维进行应用迁移时按默认的统一配置了堆内存大小，导致内存的确不够用，所以溢出了，
          今天想说的其实主要是我们的 thread dump，这也是我最近才真正用的一个方法，可能真的很小白了，用过 ide 的单步调试其实都知道会有一个一层层的玩意，比如函数从 A，调用了 B，再从 B 调用了 C，一直往下(因为是 Java，所以还有很多🤦‍♂️)，这个其实也是大部分语言的调用模型，利用了栈这个数据结构，通过这个结构我们可以知道代码的调用链路，由于对于一个 spring 应用，在本身框架代码量非常庞大的情况下，外加如果应用代码也是非常多的时候，有时候通过单步调试真的很难短时间定位到问题，需要非常大的耐心和仔细观察，当然不是说完全不行，举个例子当我的应用经常启动需要非常长的时间，因为本身应用有非常多个 bean，比较难说究竟是 bean 的加载的确很慢还是有什么异常原因，这种时候就可以使用 thread dump 了，具体怎么操作呢

          如果在idea 中运行或者调试时，可以直接点击这个照相机一样的按钮，右边就会出现了左边会显示所有的线程，右边会显示线程栈，

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          "main@1" prio=5 tid=0x1 nid=NA runnable
            java.lang.Thread.State: RUNNABLE
          	  at TreeDistance.treeDist(TreeDistance.java:64)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.treeDist(TreeDistance.java:65)
          	  at TreeDistance.main(TreeDistance.java:45)
          +

          这就是我们主线程的堆栈信息了，main 表示这个线程名，prio表示优先级，默认是 5，tid 表示线程 id，nid 表示对应的系统线程，后面的runnable 表示目前线程状态，因为是被我打了断点，所以是就许状态，然后下面就是对应的线程栈内容了，在TreeDistance类的 treeDist方法中，对应的文件行数是 64 行。
          这里使用 thread dump一般也不会是上面我截图代码里的这种代码量很少的，一般是大型项目，有时候跑着跑着没反应，又不知道跑到哪了，特别是一些刚接触的大项目或者需要定位一个大项目的一个疑难问题，一时没思路时，可以使用这个方法，个人觉得非常有帮助。

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          - - - - - Posted on - - - - - - - - Edited on - - - - - - - In - - - - , - - - - , - - - - , - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
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          LRU

          说完了过期策略再说下淘汰策略，redis 使用的策略是近似的 lru 策略，为什么是近似的呢，先来看下什么是 lru，看下 wiki 的介绍
          ，图中一共有四个槽的存储空间，依次访问顺序是 A B C D E D F，
          当第一次访问 D 时刚好占满了坑，并且值是 4，这个值越小代表越先被淘汰，当 E 进来时，看了下已经存在的四个里 A 是最小的，代表是最早存在并且最早被访问的，那就先淘汰它了，E 占领了 A 的位置，并设置值为 4，然后又访问 D 了，D 已经存在了，不过又被访问到了，得更新值为 5，然后是 F 进来了，这时 B 是最老的且最近未被访问，所以就淘汰它了。以上是一个 lru 的简要说明，但是 redis 没有严格按照这个去执行，理由跟前面过期策略一致，最严格的过期策略应该是每个 key 都有对应的定时器，当超时时马上就能清除，但是问题是这样的cpu 消耗太大，所换来的内存效率不太值得，淘汰策略也是这样，类似于上图，要维护所有 key 的一个有序 lru 值，并且遍历将最小的淘汰，redis 采用的是抽样的形式，最初的实现方式是随机从 dict 抽取 5 个 key，淘汰一个 lru 最小的，这样子勉强能达到淘汰的目的，但是效果不是特别好，后面在 redis 3.0开始，将随机抽取改成了维护一个 pool，pool 的大小默认是 16，每次放入的都是按lru 值有序排列好，每一次放入的必须是 lru小于 pool 中最小的 lru 才允许放入，直到放满，后面再有新的就会将大的踢出。
          redis 针对这个策略的改进做了一个实验，这里借用下图

          首先背景是这图中的所有点都对应一个 redis 的 key，灰色部分加入后被顺序访问过一遍，然后又加入了绿色部分，那么按照理论的 lru 算法，应该是图左上中，浅灰色部分全都被淘汰，那么对比来看看图右上，左下和右下，左下表示 2.8 版本就是随机抽样 5 个 key，淘汰其中 lru 最小的一个，发现是灰色和浅灰色的都有被淘汰的，右下的 3.0 版本抽样数量不变的情况下，稍好一些，当 3.0 版本的抽样数量调整成 10 后，已经较为接近理论上的 lru 策略了，通过代码来简要分析下

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          typedef struct redisObject {
              unsigned type:4;
              unsigned encoding:4;
              unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
                                      * LFU data (least significant 8 bits frequency
                                      * and most significant 16 bits access time). */
              int refcount;
              void *ptr;
          } robj;
          -

          对于 lru 策略来说，lru 字段记录的就是redisObj 的LRU time，
          redis 在访问数据时，都会调用lookupKey方法

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          /* Low level key lookup API, not actually called directly from commands
           * implementations that should instead rely on lookupKeyRead(),
           * lookupKeyWrite() and lookupKeyReadWithFlags(). */
          robj *lookupKey(redisDb *db, robj *key, int flags) {
              dictEntry *de = dictFind(db->dict,key->ptr);
              if (de) {
                  robj *val = dictGetVal(de);

                  /* Update the access time for the ageing algorithm.
                   * Don't do it if we have a saving child, as this will trigger
                   * a copy on write madness. */
                  if (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){
                      if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                          // 这个是后面一节的内容
                          updateLFU(val);
                      } else {
                          //  对于这个分支，访问时就会去更新 lru 值
                          val->lru = LRU_CLOCK();
                      }
                  }
                  return val;
              } else {
                  return NULL;
              }
          }
          /* This function is used to obtain the current LRU clock.
           * If the current resolution is lower than the frequency we refresh the
           * LRU clock (as it should be in production servers) we return the
           * precomputed value, otherwise we need to resort to a system call. */
          unsigned int LRU_CLOCK(void) {
              unsigned int lruclock;
              if (1000/server.hz <= LRU_CLOCK_RESOLUTION) {
                  // 如果服务器的频率server.hz大于 1 时就是用系统预设的 lruclock
                  lruclock = server.lruclock;
              } else {
                  lruclock = getLRUClock();
              }
              return lruclock;
          }
          /* Return the LRU clock, based on the clock resolution. This is a time
           * in a reduced-bits format that can be used to set and check the
           * object->lru field of redisObject structures. */
          unsigned int getLRUClock(void) {
              return (mstime()/LRU_CLOCK_RESOLUTION) & LRU_CLOCK_MAX;
          }
          -

          redis 处理命令是在这里processCommand

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          /* If this function gets called we already read a whole
           * command, arguments are in the client argv/argc fields.
           * processCommand() execute the command or prepare the
           * server for a bulk read from the client.
           *
           * If C_OK is returned the client is still alive and valid and
           * other operations can be performed by the caller. Otherwise
           * if C_ERR is returned the client was destroyed (i.e. after QUIT). */
          int processCommand(client *c) {
              moduleCallCommandFilters(c);

              

              /* Handle the maxmemory directive.
               *
               * Note that we do not want to reclaim memory if we are here re-entering
               * the event loop since there is a busy Lua script running in timeout
               * condition, to avoid mixing the propagation of scripts with the
               * propagation of DELs due to eviction. */
              if (server.maxmemory && !server.lua_timedout) {
                  int out_of_memory = freeMemoryIfNeededAndSafe() == C_ERR;
                  /* freeMemoryIfNeeded may flush slave output buffers. This may result
                   * into a slave, that may be the active client, to be freed. */
                  if (server.current_client == NULL) return C_ERR;

                  /* It was impossible to free enough memory, and the command the client
                   * is trying to execute is denied during OOM conditions or the client
                   * is in MULTI/EXEC context? Error. */
                  if (out_of_memory &&
                      (c->cmd->flags & CMD_DENYOOM ||
                       (c->flags & CLIENT_MULTI &&
                        c->cmd->proc != execCommand &&
                        c->cmd->proc != discardCommand)))
                  {
                      flagTransaction(c);
                      addReply(c, shared.oomerr);
                      return C_OK;
                  }
              }
          }
          -

          这里只摘了部分，当需要清理内存时就会调用, 然后调用了freeMemoryIfNeededAndSafe

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          /* This is a wrapper for freeMemoryIfNeeded() that only really calls the
           * function if right now there are the conditions to do so safely:
           *
           * - There must be no script in timeout condition.
           * - Nor we are loading data right now.
           *
           */
          int freeMemoryIfNeededAndSafe(void) {
              if (server.lua_timedout || server.loading) return C_OK;
              return freeMemoryIfNeeded();
          }
          /* This function is periodically called to see if there is memory to free
           * according to the current "maxmemory" settings. In case we are over the
           * memory limit, the function will try to free some memory to return back
           * under the limit.
           *
           * The function returns C_OK if we are under the memory limit or if we
           * were over the limit, but the attempt to free memory was successful.
           * Otehrwise if we are over the memory limit, but not enough memory
           * was freed to return back under the limit, the function returns C_ERR. */
          int freeMemoryIfNeeded(void) {
              int keys_freed = 0;
              /* By default replicas should ignore maxmemory
               * and just be masters exact copies. */
              if (server.masterhost && server.repl_slave_ignore_maxmemory) return C_OK;

              size_t mem_reported, mem_tofree, mem_freed;
              mstime_t latency, eviction_latency;
              long long delta;
              int slaves = listLength(server.slaves);

              /* When clients are paused the dataset should be static not just from the
               * POV of clients not being able to write, but also from the POV of
               * expires and evictions of keys not being performed. */
              if (clientsArePaused()) return C_OK;
              if (getMaxmemoryState(&mem_reported,NULL,&mem_tofree,NULL) == C_OK)
                  return C_OK;

              mem_freed = 0;

              if (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)
                  goto cant_free; /* We need to free memory, but policy forbids. */

              latencyStartMonitor(latency);
              while (mem_freed < mem_tofree) {
                  int j, k, i;
                  static unsigned int next_db = 0;
                  sds bestkey = NULL;
                  int bestdbid;
                  redisDb *db;
                  dict *dict;
                  dictEntry *de;

                  if (server.maxmemory_policy & (MAXMEMORY_FLAG_LRU|MAXMEMORY_FLAG_LFU) ||
                      server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL)
                  {
                      struct evictionPoolEntry *pool = EvictionPoolLRU;

                      while(bestkey == NULL) {
                          unsigned long total_keys = 0, keys;

                          /* We don't want to make local-db choices when expiring keys,
                           * so to start populate the eviction pool sampling keys from
                           * every DB. */
                          for (i = 0; i < server.dbnum; i++) {
                              db = server.db+i;
                              dict = (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) ?
                                      db->dict : db->expires;
                              if ((keys = dictSize(dict)) != 0) {
                                  evictionPoolPopulate(i, dict, db->dict, pool);
                                  total_keys += keys;
                              }
                          }
                          if (!total_keys) break; /* No keys to evict. */

                          /* Go backward from best to worst element to evict. */
                          for (k = EVPOOL_SIZE-1; k >= 0; k--) {
                              if (pool[k].key == NULL) continue;
                              bestdbid = pool[k].dbid;

                              if (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) {
                                  de = dictFind(server.db[pool[k].dbid].dict,
                                      pool[k].key);
                              } else {
                                  de = dictFind(server.db[pool[k].dbid].expires,
                                      pool[k].key);
                              }

                              /* Remove the entry from the pool. */
                              if (pool[k].key != pool[k].cached)
                                  sdsfree(pool[k].key);
                              pool[k].key = NULL;
                              pool[k].idle = 0;

                              /* If the key exists, is our pick. Otherwise it is
                               * a ghost and we need to try the next element. */
                              if (de) {
                                  bestkey = dictGetKey(de);
                                  break;
                              } else {
                                  /* Ghost... Iterate again. */
                              }
                          }
                      }
                  }

                  /* volatile-random and allkeys-random policy */
                  else if (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM ||
                           server.maxmemory_policy == MAXMEMORY_VOLATILE_RANDOM)
                  {
                      /* When evicting a random key, we try to evict a key for
                       * each DB, so we use the static 'next_db' variable to
                       * incrementally visit all DBs. */
                      for (i = 0; i < server.dbnum; i++) {
                          j = (++next_db) % server.dbnum;
                          db = server.db+j;
                          dict = (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM) ?
                                  db->dict : db->expires;
                          if (dictSize(dict) != 0) {
                              de = dictGetRandomKey(dict);
                              bestkey = dictGetKey(de);
                              bestdbid = j;
                              break;
                          }
                      }
                  }

                  /* Finally remove the selected key. */
                  if (bestkey) {
                      db = server.db+bestdbid;
                      robj *keyobj = createStringObject(bestkey,sdslen(bestkey));
                      propagateExpire(db,keyobj,server.lazyfree_lazy_eviction);
                      /* We compute the amount of memory freed by db*Delete() alone.
                       * It is possible that actually the memory needed to propagate
                       * the DEL in AOF and replication link is greater than the one
                       * we are freeing removing the key, but we can't account for
                       * that otherwise we would never exit the loop.
                       *
                       * AOF and Output buffer memory will be freed eventually so
                       * we only care about memory used by the key space. */
                      delta = (long long) zmalloc_used_memory();
                      latencyStartMonitor(eviction_latency);
                      if (server.lazyfree_lazy_eviction)
                          dbAsyncDelete(db,keyobj);
                      else
                          dbSyncDelete(db,keyobj);
                      latencyEndMonitor(eviction_latency);
                      latencyAddSampleIfNeeded("eviction-del",eviction_latency);
                      latencyRemoveNestedEvent(latency,eviction_latency);
                      delta -= (long long) zmalloc_used_memory();
                      mem_freed += delta;
                      server.stat_evictedkeys++;
                      notifyKeyspaceEvent(NOTIFY_EVICTED, "evicted",
                          keyobj, db->id);
                      decrRefCount(keyobj);
                      keys_freed++;

                      /* When the memory to free starts to be big enough, we may
                       * start spending so much time here that is impossible to
                       * deliver data to the slaves fast enough, so we force the
                       * transmission here inside the loop. */
                      if (slaves) flushSlavesOutputBuffers();

                      /* Normally our stop condition is the ability to release
                       * a fixed, pre-computed amount of memory. However when we
                       * are deleting objects in another thread, it's better to
                       * check, from time to time, if we already reached our target
                       * memory, since the "mem_freed" amount is computed only
                       * across the dbAsyncDelete() call, while the thread can
                       * release the memory all the time. */
                      if (server.lazyfree_lazy_eviction && !(keys_freed % 16)) {
                          if (getMaxmemoryState(NULL,NULL,NULL,NULL) == C_OK) {
                              /* Let's satisfy our stop condition. */
                              mem_freed = mem_tofree;
                          }
                      }
                  } else {
                      latencyEndMonitor(latency);
                      latencyAddSampleIfNeeded("eviction-cycle",latency);
                      goto cant_free; /* nothing to free... */
                  }
              }
              latencyEndMonitor(latency);
              latencyAddSampleIfNeeded("eviction-cycle",latency);
              return C_OK;

          cant_free:
              /* We are here if we are not able to reclaim memory. There is only one
               * last thing we can try: check if the lazyfree thread has jobs in queue
               * and wait... */
              while(bioPendingJobsOfType(BIO_LAZY_FREE)) {
                  if (((mem_reported - zmalloc_used_memory()) + mem_freed) >= mem_tofree)
                      break;
                  usleep(1000);
              }
              return C_ERR;
          }
          -

          这里就是根据具体策略去淘汰 key，首先是要往 pool 更新 key，更新key 的方法是evictionPoolPopulate

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          void evictionPoolPopulate(int dbid, dict *sampledict, dict *keydict, struct evictionPoolEntry *pool) {
              int j, k, count;
              dictEntry *samples[server.maxmemory_samples];

              count = dictGetSomeKeys(sampledict,samples,server.maxmemory_samples);
              for (j = 0; j < count; j++) {
                  unsigned long long idle;
                  sds key;
                  robj *o;
                  dictEntry *de;

                  de = samples[j];
                  key = dictGetKey(de);

                  /* If the dictionary we are sampling from is not the main
                   * dictionary (but the expires one) we need to lookup the key
                   * again in the key dictionary to obtain the value object. */
                  if (server.maxmemory_policy != MAXMEMORY_VOLATILE_TTL) {
                      if (sampledict != keydict) de = dictFind(keydict, key);
                      o = dictGetVal(de);
                  }

                  /* Calculate the idle time according to the policy. This is called
                   * idle just because the code initially handled LRU, but is in fact
                   * just a score where an higher score means better candidate. */
                  if (server.maxmemory_policy & MAXMEMORY_FLAG_LRU) {
                      idle = estimateObjectIdleTime(o);
                  } else if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                      /* When we use an LRU policy, we sort the keys by idle time
                       * so that we expire keys starting from greater idle time.
                       * However when the policy is an LFU one, we have a frequency
                       * estimation, and we want to evict keys with lower frequency
                       * first. So inside the pool we put objects using the inverted
                       * frequency subtracting the actual frequency to the maximum
                       * frequency of 255. */
                      idle = 255-LFUDecrAndReturn(o);
                  } else if (server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL) {
                      /* In this case the sooner the expire the better. */
                      idle = ULLONG_MAX - (long)dictGetVal(de);
                  } else {
                      serverPanic("Unknown eviction policy in evictionPoolPopulate()");
                  }

                  /* Insert the element inside the pool.
                   * First, find the first empty bucket or the first populated
                   * bucket that has an idle time smaller than our idle time. */
                  k = 0;
                  while (k < EVPOOL_SIZE &&
                         pool[k].key &&
                         pool[k].idle < idle) k++;
                  if (k == 0 && pool[EVPOOL_SIZE-1].key != NULL) {
                      /* Can't insert if the element is < the worst element we have
                       * and there are no empty buckets. */
                      continue;
                  } else if (k < EVPOOL_SIZE && pool[k].key == NULL) {
                      /* Inserting into empty position. No setup needed before insert. */
                  } else {
                      /* Inserting in the middle. Now k points to the first element
                       * greater than the element to insert.  */
                      if (pool[EVPOOL_SIZE-1].key == NULL) {
                          /* Free space on the right? Insert at k shifting
                           * all the elements from k to end to the right. */

                          /* Save SDS before overwriting. */
                          sds cached = pool[EVPOOL_SIZE-1].cached;
                          memmove(pool+k+1,pool+k,
                              sizeof(pool[0])*(EVPOOL_SIZE-k-1));
                          pool[k].cached = cached;
                      } else {
                          /* No free space on right? Insert at k-1 */
                          k--;
                          /* Shift all elements on the left of k (included) to the
                           * left, so we discard the element with smaller idle time. */
                          sds cached = pool[0].cached; /* Save SDS before overwriting. */
                          if (pool[0].key != pool[0].cached) sdsfree(pool[0].key);
                          memmove(pool,pool+1,sizeof(pool[0])*k);
                          pool[k].cached = cached;
                      }
                  }

                  /* Try to reuse the cached SDS string allocated in the pool entry,
                   * because allocating and deallocating this object is costly
                   * (according to the profiler, not my fantasy. Remember:
                   * premature optimizbla bla bla bla. */
                  int klen = sdslen(key);
                  if (klen > EVPOOL_CACHED_SDS_SIZE) {
                      pool[k].key = sdsdup(key);
                  } else {
                      memcpy(pool[k].cached,key,klen+1);
                      sdssetlen(pool[k].cached,klen);
                      pool[k].key = pool[k].cached;
                  }
                  pool[k].idle = idle;
                  pool[k].dbid = dbid;
              }
          }
          -

          Redis随机选择maxmemory_samples数量的key，然后计算这些key的空闲时间idle time，当满足条件时(比pool中的某些键的空闲时间还大)就可以进pool。pool更新之后，就淘汰pool中空闲时间最大的键。

          -

          estimateObjectIdleTime用来计算Redis对象的空闲时间：

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          /* Given an object returns the min number of milliseconds the object was never
           * requested, using an approximated LRU algorithm. */
          unsigned long long estimateObjectIdleTime(robj *o) {
              unsigned long long lruclock = LRU_CLOCK();
              if (lruclock >= o->lru) {
                  return (lruclock - o->lru) * LRU_CLOCK_RESOLUTION;
              } else {
                  return (lruclock + (LRU_CLOCK_MAX - o->lru)) *
                              LRU_CLOCK_RESOLUTION;
              }
          }
          -

          空闲时间第一种是 lurclock 大于对象的 lru，那么就是减一下乘以精度，因为 lruclock 有可能是已经预生成的，所以会可能走下面这个

          -

          LFU

          上面介绍了LRU 的算法，但是考虑一种场景

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          ~~~~~A~~~~~A~~~~~A~~~~A~~~~~A~~~~~A~~|
          ~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~|
          ~~~~~~~~~~C~~~~~~~~~C~~~~~~~~~C~~~~~~|
          ~~~~~D~~~~~~~~~~D~~~~~~~~~D~~~~~~~~~D|
          -

          可以发现，当采用 lru 的淘汰策略的时候，D 是最新的，会被认为是最值得保留的，但是事实上还不如 A 跟 B，然后 antirez 大神就想到了LFU (Least Frequently Used) 这个算法, 显然对于上面的四个 key 的访问频率，保留优先级应该是 B > A > C = D
          那要怎么来实现这个 LFU 算法呢，其实像LRU，理想的情况就是维护个链表，把最新访问的放到头上去，但是这个会影响访问速度，注意到前面代码的应该可以看到，redisObject 的 lru 字段其实是两用的，当策略是 LFU 时，这个字段就另作他用了，它的 24 位长度被分成两部分

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                16 bits      8 bits
          +----------------+--------+
          + Last decr time | LOG_C  |
          +----------------+--------+
          -

          前16位字段是最后一次递减时间，因此Redis知道 上一次计数器递减，后8位是 计数器 counter。
          LFU 的主体策略就是当这个 key 被访问的次数越多频率越高他就越容易被保留下来，并且是最近被访问的频率越高。这其实有两个事情要做，一个是在访问的时候增加计数值，在一定长时间不访问时进行衰减，所以这里用了两个值，前 16 位记录上一次衰减的时间，后 8 位记录具体的计数值。
          Redis4.0之后为maxmemory_policy淘汰策略添加了两个LFU模式：

          -

          volatile-lfu：对有过期时间的key采用LFU淘汰策略
          allkeys-lfu：对全部key采用LFU淘汰策略
          还有2个配置可以调整LFU算法：

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          lfu-log-factor 10
          lfu-decay-time 1
          ```  
          `lfu-log-factor` 可以调整计数器counter的增长速度，lfu-log-factor越大，counter增长的越慢。

          `lfu-decay-time`是一个以分钟为单位的数值，可以调整counter的减少速度
          这里有个问题是 8 位大小够计么，访问一次加 1 的话的确不够，不过大神就是大神，才不会这么简单的加一。往下看代码
          ```C
          /* Low level key lookup API, not actually called directly from commands
           * implementations that should instead rely on lookupKeyRead(),
           * lookupKeyWrite() and lookupKeyReadWithFlags(). */
          robj *lookupKey(redisDb *db, robj *key, int flags) {
              dictEntry *de = dictFind(db->dict,key->ptr);
              if (de) {
                  robj *val = dictGetVal(de);

                  /* Update the access time for the ageing algorithm.
                   * Don't do it if we have a saving child, as this will trigger
                   * a copy on write madness. */
                  if (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){
                      if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                          // 当淘汰策略是 LFU 时，就会调用这个updateLFU
                          updateLFU(val);
                      } else {
                          val->lru = LRU_CLOCK();
                      }
                  }
                  return val;
              } else {
                  return NULL;
              }
          }
          -

          updateLFU 这个其实个入口，调用了两个重要的方法

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          /* Update LFU when an object is accessed.
           * Firstly, decrement the counter if the decrement time is reached.
           * Then logarithmically increment the counter, and update the access time. */
          void updateLFU(robj *val) {
              unsigned long counter = LFUDecrAndReturn(val);
              counter = LFULogIncr(counter);
              val->lru = (LFUGetTimeInMinutes()<<8) | counter;
          }
          -

          首先来看看LFUDecrAndReturn，这个方法的作用是根据上一次衰减时间和系统配置的 lfu-decay-time 参数来确定需要将 counter 减去多少

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          /* If the object decrement time is reached decrement the LFU counter but
           * do not update LFU fields of the object, we update the access time
           * and counter in an explicit way when the object is really accessed.
           * And we will times halve the counter according to the times of
           * elapsed time than server.lfu_decay_time.
           * Return the object frequency counter.
           *
           * This function is used in order to scan the dataset for the best object
           * to fit: as we check for the candidate, we incrementally decrement the
           * counter of the scanned objects if needed. */
          unsigned long LFUDecrAndReturn(robj *o) {
              // 右移 8 位，拿到上次衰减时间
              unsigned long ldt = o->lru >> 8;
              // 对 255 做与操作，拿到 counter 值
              unsigned long counter = o->lru & 255;
              // 根据lfu_decay_time来算出过了多少个衰减周期
              unsigned long num_periods = server.lfu_decay_time ? LFUTimeElapsed(ldt) / server.lfu_decay_time : 0;
              if (num_periods)
                  counter = (num_periods > counter) ? 0 : counter - num_periods;
              return counter;
          }
          -

          然后是加，调用了LFULogIncr

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          /* Logarithmically increment a counter. The greater is the current counter value
           * the less likely is that it gets really implemented. Saturate it at 255. */
          uint8_t LFULogIncr(uint8_t counter) {
              // 最大值就是 255，到顶了就不加了
              if (counter == 255) return 255;
              // 生成个随机小数
              double r = (double)rand()/RAND_MAX;
              // 减去个基础值，LFU_INIT_VAL = 5，防止刚进来就被逐出
              double baseval = counter - LFU_INIT_VAL;
              // 如果是小于 0，
              if (baseval < 0) baseval = 0;
              // 如果 baseval 是 0，那么 p 就是 1了，后面 counter 直接加一，如果不是的话，得看系统参数lfu_log_factor，这个越大，除出来的 p 越小，那么 counter++的可能性也越小，这样子就把前面的疑问给解决了，不是直接+1 的
              double p = 1.0/(baseval*server.lfu_log_factor+1);
              if (r < p) counter++;
              return counter;
          }
          -

          大概的变化速度可以参考

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          +--------+------------+------------+------------+------------+------------+
          | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |
          +--------+------------+------------+------------+------------+------------+
          | 0      | 104        | 255        | 255        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 1      | 18         | 49         | 255        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 10     | 10         | 18         | 142        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 100    | 8          | 11         | 49         | 143        | 255        |
          +--------+------------+------------+------------+------------+------------+
          -

          简而言之就是 lfu_log_factor 越大变化的越慢

          -

          总结

          总结一下，redis 实现了近似的 lru 淘汰策略，通过增加了淘汰 key 的池子(pool)，并且增大每次抽样的 key 的数量来将淘汰效果更进一步地接近于 lru，这是 lru 策略，但是对于前面举的一个例子，其实 lru 并不能保证 key 的淘汰就如我们预期，所以在后期又引入了 lfu 的策略，lfu的策略比较巧妙，复用了 redis 对象的 lru 字段，并且使用了factor 参数来控制计数器递增的速度，防止 8 位的计数器太早溢出。

          - - -
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          - - - - @@ -917,20 +885,20 @@
          - 70 + 71 posts
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          - +
          diff --git a/page/6/index.html b/page/6/index.html index 92db0560cd..5698d33c5b 100644 --- a/page/6/index.html +++ b/page/6/index.html @@ -203,6 +203,149 @@ +
          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + Edited on + + + + + + + In + + + + , + + + + , + + + + , + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          LRU

          说完了过期策略再说下淘汰策略，redis 使用的策略是近似的 lru 策略，为什么是近似的呢，先来看下什么是 lru，看下 wiki 的介绍
          ，图中一共有四个槽的存储空间，依次访问顺序是 A B C D E D F，
          当第一次访问 D 时刚好占满了坑，并且值是 4，这个值越小代表越先被淘汰，当 E 进来时，看了下已经存在的四个里 A 是最小的，代表是最早存在并且最早被访问的，那就先淘汰它了，E 占领了 A 的位置，并设置值为 4，然后又访问 D 了，D 已经存在了，不过又被访问到了，得更新值为 5，然后是 F 进来了，这时 B 是最老的且最近未被访问，所以就淘汰它了。以上是一个 lru 的简要说明，但是 redis 没有严格按照这个去执行，理由跟前面过期策略一致，最严格的过期策略应该是每个 key 都有对应的定时器，当超时时马上就能清除，但是问题是这样的cpu 消耗太大，所换来的内存效率不太值得，淘汰策略也是这样，类似于上图，要维护所有 key 的一个有序 lru 值，并且遍历将最小的淘汰，redis 采用的是抽样的形式，最初的实现方式是随机从 dict 抽取 5 个 key，淘汰一个 lru 最小的，这样子勉强能达到淘汰的目的，但是效果不是特别好，后面在 redis 3.0开始，将随机抽取改成了维护一个 pool，pool 的大小默认是 16，每次放入的都是按lru 值有序排列好，每一次放入的必须是 lru小于 pool 中最小的 lru 才允许放入，直到放满，后面再有新的就会将大的踢出。
          redis 针对这个策略的改进做了一个实验，这里借用下图

          首先背景是这图中的所有点都对应一个 redis 的 key，灰色部分加入后被顺序访问过一遍，然后又加入了绿色部分，那么按照理论的 lru 算法，应该是图左上中，浅灰色部分全都被淘汰，那么对比来看看图右上，左下和右下，左下表示 2.8 版本就是随机抽样 5 个 key，淘汰其中 lru 最小的一个，发现是灰色和浅灰色的都有被淘汰的，右下的 3.0 版本抽样数量不变的情况下，稍好一些，当 3.0 版本的抽样数量调整成 10 后，已经较为接近理论上的 lru 策略了，通过代码来简要分析下

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          typedef struct redisObject {
              unsigned type:4;
              unsigned encoding:4;
              unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
                                      * LFU data (least significant 8 bits frequency
                                      * and most significant 16 bits access time). */
              int refcount;
              void *ptr;
          } robj;
          +

          对于 lru 策略来说，lru 字段记录的就是redisObj 的LRU time，
          redis 在访问数据时，都会调用lookupKey方法

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          /* Low level key lookup API, not actually called directly from commands
           * implementations that should instead rely on lookupKeyRead(),
           * lookupKeyWrite() and lookupKeyReadWithFlags(). */
          robj *lookupKey(redisDb *db, robj *key, int flags) {
              dictEntry *de = dictFind(db->dict,key->ptr);
              if (de) {
                  robj *val = dictGetVal(de);

                  /* Update the access time for the ageing algorithm.
                   * Don't do it if we have a saving child, as this will trigger
                   * a copy on write madness. */
                  if (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){
                      if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                          // 这个是后面一节的内容
                          updateLFU(val);
                      } else {
                          //  对于这个分支，访问时就会去更新 lru 值
                          val->lru = LRU_CLOCK();
                      }
                  }
                  return val;
              } else {
                  return NULL;
              }
          }
          /* This function is used to obtain the current LRU clock.
           * If the current resolution is lower than the frequency we refresh the
           * LRU clock (as it should be in production servers) we return the
           * precomputed value, otherwise we need to resort to a system call. */
          unsigned int LRU_CLOCK(void) {
              unsigned int lruclock;
              if (1000/server.hz <= LRU_CLOCK_RESOLUTION) {
                  // 如果服务器的频率server.hz大于 1 时就是用系统预设的 lruclock
                  lruclock = server.lruclock;
              } else {
                  lruclock = getLRUClock();
              }
              return lruclock;
          }
          /* Return the LRU clock, based on the clock resolution. This is a time
           * in a reduced-bits format that can be used to set and check the
           * object->lru field of redisObject structures. */
          unsigned int getLRUClock(void) {
              return (mstime()/LRU_CLOCK_RESOLUTION) & LRU_CLOCK_MAX;
          }
          +

          redis 处理命令是在这里processCommand

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          /* If this function gets called we already read a whole
           * command, arguments are in the client argv/argc fields.
           * processCommand() execute the command or prepare the
           * server for a bulk read from the client.
           *
           * If C_OK is returned the client is still alive and valid and
           * other operations can be performed by the caller. Otherwise
           * if C_ERR is returned the client was destroyed (i.e. after QUIT). */
          int processCommand(client *c) {
              moduleCallCommandFilters(c);

              

              /* Handle the maxmemory directive.
               *
               * Note that we do not want to reclaim memory if we are here re-entering
               * the event loop since there is a busy Lua script running in timeout
               * condition, to avoid mixing the propagation of scripts with the
               * propagation of DELs due to eviction. */
              if (server.maxmemory && !server.lua_timedout) {
                  int out_of_memory = freeMemoryIfNeededAndSafe() == C_ERR;
                  /* freeMemoryIfNeeded may flush slave output buffers. This may result
                   * into a slave, that may be the active client, to be freed. */
                  if (server.current_client == NULL) return C_ERR;

                  /* It was impossible to free enough memory, and the command the client
                   * is trying to execute is denied during OOM conditions or the client
                   * is in MULTI/EXEC context? Error. */
                  if (out_of_memory &&
                      (c->cmd->flags & CMD_DENYOOM ||
                       (c->flags & CLIENT_MULTI &&
                        c->cmd->proc != execCommand &&
                        c->cmd->proc != discardCommand)))
                  {
                      flagTransaction(c);
                      addReply(c, shared.oomerr);
                      return C_OK;
                  }
              }
          }
          +

          这里只摘了部分，当需要清理内存时就会调用, 然后调用了freeMemoryIfNeededAndSafe

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          /* This is a wrapper for freeMemoryIfNeeded() that only really calls the
           * function if right now there are the conditions to do so safely:
           *
           * - There must be no script in timeout condition.
           * - Nor we are loading data right now.
           *
           */
          int freeMemoryIfNeededAndSafe(void) {
              if (server.lua_timedout || server.loading) return C_OK;
              return freeMemoryIfNeeded();
          }
          /* This function is periodically called to see if there is memory to free
           * according to the current "maxmemory" settings. In case we are over the
           * memory limit, the function will try to free some memory to return back
           * under the limit.
           *
           * The function returns C_OK if we are under the memory limit or if we
           * were over the limit, but the attempt to free memory was successful.
           * Otehrwise if we are over the memory limit, but not enough memory
           * was freed to return back under the limit, the function returns C_ERR. */
          int freeMemoryIfNeeded(void) {
              int keys_freed = 0;
              /* By default replicas should ignore maxmemory
               * and just be masters exact copies. */
              if (server.masterhost && server.repl_slave_ignore_maxmemory) return C_OK;

              size_t mem_reported, mem_tofree, mem_freed;
              mstime_t latency, eviction_latency;
              long long delta;
              int slaves = listLength(server.slaves);

              /* When clients are paused the dataset should be static not just from the
               * POV of clients not being able to write, but also from the POV of
               * expires and evictions of keys not being performed. */
              if (clientsArePaused()) return C_OK;
              if (getMaxmemoryState(&mem_reported,NULL,&mem_tofree,NULL) == C_OK)
                  return C_OK;

              mem_freed = 0;

              if (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)
                  goto cant_free; /* We need to free memory, but policy forbids. */

              latencyStartMonitor(latency);
              while (mem_freed < mem_tofree) {
                  int j, k, i;
                  static unsigned int next_db = 0;
                  sds bestkey = NULL;
                  int bestdbid;
                  redisDb *db;
                  dict *dict;
                  dictEntry *de;

                  if (server.maxmemory_policy & (MAXMEMORY_FLAG_LRU|MAXMEMORY_FLAG_LFU) ||
                      server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL)
                  {
                      struct evictionPoolEntry *pool = EvictionPoolLRU;

                      while(bestkey == NULL) {
                          unsigned long total_keys = 0, keys;

                          /* We don't want to make local-db choices when expiring keys,
                           * so to start populate the eviction pool sampling keys from
                           * every DB. */
                          for (i = 0; i < server.dbnum; i++) {
                              db = server.db+i;
                              dict = (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) ?
                                      db->dict : db->expires;
                              if ((keys = dictSize(dict)) != 0) {
                                  evictionPoolPopulate(i, dict, db->dict, pool);
                                  total_keys += keys;
                              }
                          }
                          if (!total_keys) break; /* No keys to evict. */

                          /* Go backward from best to worst element to evict. */
                          for (k = EVPOOL_SIZE-1; k >= 0; k--) {
                              if (pool[k].key == NULL) continue;
                              bestdbid = pool[k].dbid;

                              if (server.maxmemory_policy & MAXMEMORY_FLAG_ALLKEYS) {
                                  de = dictFind(server.db[pool[k].dbid].dict,
                                      pool[k].key);
                              } else {
                                  de = dictFind(server.db[pool[k].dbid].expires,
                                      pool[k].key);
                              }

                              /* Remove the entry from the pool. */
                              if (pool[k].key != pool[k].cached)
                                  sdsfree(pool[k].key);
                              pool[k].key = NULL;
                              pool[k].idle = 0;

                              /* If the key exists, is our pick. Otherwise it is
                               * a ghost and we need to try the next element. */
                              if (de) {
                                  bestkey = dictGetKey(de);
                                  break;
                              } else {
                                  /* Ghost... Iterate again. */
                              }
                          }
                      }
                  }

                  /* volatile-random and allkeys-random policy */
                  else if (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM ||
                           server.maxmemory_policy == MAXMEMORY_VOLATILE_RANDOM)
                  {
                      /* When evicting a random key, we try to evict a key for
                       * each DB, so we use the static 'next_db' variable to
                       * incrementally visit all DBs. */
                      for (i = 0; i < server.dbnum; i++) {
                          j = (++next_db) % server.dbnum;
                          db = server.db+j;
                          dict = (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM) ?
                                  db->dict : db->expires;
                          if (dictSize(dict) != 0) {
                              de = dictGetRandomKey(dict);
                              bestkey = dictGetKey(de);
                              bestdbid = j;
                              break;
                          }
                      }
                  }

                  /* Finally remove the selected key. */
                  if (bestkey) {
                      db = server.db+bestdbid;
                      robj *keyobj = createStringObject(bestkey,sdslen(bestkey));
                      propagateExpire(db,keyobj,server.lazyfree_lazy_eviction);
                      /* We compute the amount of memory freed by db*Delete() alone.
                       * It is possible that actually the memory needed to propagate
                       * the DEL in AOF and replication link is greater than the one
                       * we are freeing removing the key, but we can't account for
                       * that otherwise we would never exit the loop.
                       *
                       * AOF and Output buffer memory will be freed eventually so
                       * we only care about memory used by the key space. */
                      delta = (long long) zmalloc_used_memory();
                      latencyStartMonitor(eviction_latency);
                      if (server.lazyfree_lazy_eviction)
                          dbAsyncDelete(db,keyobj);
                      else
                          dbSyncDelete(db,keyobj);
                      latencyEndMonitor(eviction_latency);
                      latencyAddSampleIfNeeded("eviction-del",eviction_latency);
                      latencyRemoveNestedEvent(latency,eviction_latency);
                      delta -= (long long) zmalloc_used_memory();
                      mem_freed += delta;
                      server.stat_evictedkeys++;
                      notifyKeyspaceEvent(NOTIFY_EVICTED, "evicted",
                          keyobj, db->id);
                      decrRefCount(keyobj);
                      keys_freed++;

                      /* When the memory to free starts to be big enough, we may
                       * start spending so much time here that is impossible to
                       * deliver data to the slaves fast enough, so we force the
                       * transmission here inside the loop. */
                      if (slaves) flushSlavesOutputBuffers();

                      /* Normally our stop condition is the ability to release
                       * a fixed, pre-computed amount of memory. However when we
                       * are deleting objects in another thread, it's better to
                       * check, from time to time, if we already reached our target
                       * memory, since the "mem_freed" amount is computed only
                       * across the dbAsyncDelete() call, while the thread can
                       * release the memory all the time. */
                      if (server.lazyfree_lazy_eviction && !(keys_freed % 16)) {
                          if (getMaxmemoryState(NULL,NULL,NULL,NULL) == C_OK) {
                              /* Let's satisfy our stop condition. */
                              mem_freed = mem_tofree;
                          }
                      }
                  } else {
                      latencyEndMonitor(latency);
                      latencyAddSampleIfNeeded("eviction-cycle",latency);
                      goto cant_free; /* nothing to free... */
                  }
              }
              latencyEndMonitor(latency);
              latencyAddSampleIfNeeded("eviction-cycle",latency);
              return C_OK;

          cant_free:
              /* We are here if we are not able to reclaim memory. There is only one
               * last thing we can try: check if the lazyfree thread has jobs in queue
               * and wait... */
              while(bioPendingJobsOfType(BIO_LAZY_FREE)) {
                  if (((mem_reported - zmalloc_used_memory()) + mem_freed) >= mem_tofree)
                      break;
                  usleep(1000);
              }
              return C_ERR;
          }
          +

          这里就是根据具体策略去淘汰 key，首先是要往 pool 更新 key，更新key 的方法是evictionPoolPopulate

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          void evictionPoolPopulate(int dbid, dict *sampledict, dict *keydict, struct evictionPoolEntry *pool) {
              int j, k, count;
              dictEntry *samples[server.maxmemory_samples];

              count = dictGetSomeKeys(sampledict,samples,server.maxmemory_samples);
              for (j = 0; j < count; j++) {
                  unsigned long long idle;
                  sds key;
                  robj *o;
                  dictEntry *de;

                  de = samples[j];
                  key = dictGetKey(de);

                  /* If the dictionary we are sampling from is not the main
                   * dictionary (but the expires one) we need to lookup the key
                   * again in the key dictionary to obtain the value object. */
                  if (server.maxmemory_policy != MAXMEMORY_VOLATILE_TTL) {
                      if (sampledict != keydict) de = dictFind(keydict, key);
                      o = dictGetVal(de);
                  }

                  /* Calculate the idle time according to the policy. This is called
                   * idle just because the code initially handled LRU, but is in fact
                   * just a score where an higher score means better candidate. */
                  if (server.maxmemory_policy & MAXMEMORY_FLAG_LRU) {
                      idle = estimateObjectIdleTime(o);
                  } else if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                      /* When we use an LRU policy, we sort the keys by idle time
                       * so that we expire keys starting from greater idle time.
                       * However when the policy is an LFU one, we have a frequency
                       * estimation, and we want to evict keys with lower frequency
                       * first. So inside the pool we put objects using the inverted
                       * frequency subtracting the actual frequency to the maximum
                       * frequency of 255. */
                      idle = 255-LFUDecrAndReturn(o);
                  } else if (server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL) {
                      /* In this case the sooner the expire the better. */
                      idle = ULLONG_MAX - (long)dictGetVal(de);
                  } else {
                      serverPanic("Unknown eviction policy in evictionPoolPopulate()");
                  }

                  /* Insert the element inside the pool.
                   * First, find the first empty bucket or the first populated
                   * bucket that has an idle time smaller than our idle time. */
                  k = 0;
                  while (k < EVPOOL_SIZE &&
                         pool[k].key &&
                         pool[k].idle < idle) k++;
                  if (k == 0 && pool[EVPOOL_SIZE-1].key != NULL) {
                      /* Can't insert if the element is < the worst element we have
                       * and there are no empty buckets. */
                      continue;
                  } else if (k < EVPOOL_SIZE && pool[k].key == NULL) {
                      /* Inserting into empty position. No setup needed before insert. */
                  } else {
                      /* Inserting in the middle. Now k points to the first element
                       * greater than the element to insert.  */
                      if (pool[EVPOOL_SIZE-1].key == NULL) {
                          /* Free space on the right? Insert at k shifting
                           * all the elements from k to end to the right. */

                          /* Save SDS before overwriting. */
                          sds cached = pool[EVPOOL_SIZE-1].cached;
                          memmove(pool+k+1,pool+k,
                              sizeof(pool[0])*(EVPOOL_SIZE-k-1));
                          pool[k].cached = cached;
                      } else {
                          /* No free space on right? Insert at k-1 */
                          k--;
                          /* Shift all elements on the left of k (included) to the
                           * left, so we discard the element with smaller idle time. */
                          sds cached = pool[0].cached; /* Save SDS before overwriting. */
                          if (pool[0].key != pool[0].cached) sdsfree(pool[0].key);
                          memmove(pool,pool+1,sizeof(pool[0])*k);
                          pool[k].cached = cached;
                      }
                  }

                  /* Try to reuse the cached SDS string allocated in the pool entry,
                   * because allocating and deallocating this object is costly
                   * (according to the profiler, not my fantasy. Remember:
                   * premature optimizbla bla bla bla. */
                  int klen = sdslen(key);
                  if (klen > EVPOOL_CACHED_SDS_SIZE) {
                      pool[k].key = sdsdup(key);
                  } else {
                      memcpy(pool[k].cached,key,klen+1);
                      sdssetlen(pool[k].cached,klen);
                      pool[k].key = pool[k].cached;
                  }
                  pool[k].idle = idle;
                  pool[k].dbid = dbid;
              }
          }
          +

          Redis随机选择maxmemory_samples数量的key，然后计算这些key的空闲时间idle time，当满足条件时(比pool中的某些键的空闲时间还大)就可以进pool。pool更新之后，就淘汰pool中空闲时间最大的键。

          +

          estimateObjectIdleTime用来计算Redis对象的空闲时间：

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          /* Given an object returns the min number of milliseconds the object was never
           * requested, using an approximated LRU algorithm. */
          unsigned long long estimateObjectIdleTime(robj *o) {
              unsigned long long lruclock = LRU_CLOCK();
              if (lruclock >= o->lru) {
                  return (lruclock - o->lru) * LRU_CLOCK_RESOLUTION;
              } else {
                  return (lruclock + (LRU_CLOCK_MAX - o->lru)) *
                              LRU_CLOCK_RESOLUTION;
              }
          }
          +

          空闲时间第一种是 lurclock 大于对象的 lru，那么就是减一下乘以精度，因为 lruclock 有可能是已经预生成的，所以会可能走下面这个

          +

          LFU

          上面介绍了LRU 的算法，但是考虑一种场景

          +
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          ~~~~~A~~~~~A~~~~~A~~~~A~~~~~A~~~~~A~~|
          ~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~~B~|
          ~~~~~~~~~~C~~~~~~~~~C~~~~~~~~~C~~~~~~|
          ~~~~~D~~~~~~~~~~D~~~~~~~~~D~~~~~~~~~D|
          +

          可以发现，当采用 lru 的淘汰策略的时候，D 是最新的，会被认为是最值得保留的，但是事实上还不如 A 跟 B，然后 antirez 大神就想到了LFU (Least Frequently Used) 这个算法, 显然对于上面的四个 key 的访问频率，保留优先级应该是 B > A > C = D
          那要怎么来实现这个 LFU 算法呢，其实像LRU，理想的情况就是维护个链表，把最新访问的放到头上去，但是这个会影响访问速度，注意到前面代码的应该可以看到，redisObject 的 lru 字段其实是两用的，当策略是 LFU 时，这个字段就另作他用了，它的 24 位长度被分成两部分

          +
          1
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          4
                16 bits      8 bits
          +----------------+--------+
          + Last decr time | LOG_C  |
          +----------------+--------+
          +

          前16位字段是最后一次递减时间，因此Redis知道 上一次计数器递减，后8位是 计数器 counter。
          LFU 的主体策略就是当这个 key 被访问的次数越多频率越高他就越容易被保留下来，并且是最近被访问的频率越高。这其实有两个事情要做，一个是在访问的时候增加计数值，在一定长时间不访问时进行衰减，所以这里用了两个值，前 16 位记录上一次衰减的时间，后 8 位记录具体的计数值。
          Redis4.0之后为maxmemory_policy淘汰策略添加了两个LFU模式：

          +

          volatile-lfu：对有过期时间的key采用LFU淘汰策略
          allkeys-lfu：对全部key采用LFU淘汰策略
          还有2个配置可以调整LFU算法：

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          lfu-log-factor 10
          lfu-decay-time 1
          ```  
          `lfu-log-factor` 可以调整计数器counter的增长速度，lfu-log-factor越大，counter增长的越慢。

          `lfu-decay-time`是一个以分钟为单位的数值，可以调整counter的减少速度
          这里有个问题是 8 位大小够计么，访问一次加 1 的话的确不够，不过大神就是大神，才不会这么简单的加一。往下看代码
          ```C
          /* Low level key lookup API, not actually called directly from commands
           * implementations that should instead rely on lookupKeyRead(),
           * lookupKeyWrite() and lookupKeyReadWithFlags(). */
          robj *lookupKey(redisDb *db, robj *key, int flags) {
              dictEntry *de = dictFind(db->dict,key->ptr);
              if (de) {
                  robj *val = dictGetVal(de);

                  /* Update the access time for the ageing algorithm.
                   * Don't do it if we have a saving child, as this will trigger
                   * a copy on write madness. */
                  if (!hasActiveChildProcess() && !(flags & LOOKUP_NOTOUCH)){
                      if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
                          // 当淘汰策略是 LFU 时，就会调用这个updateLFU
                          updateLFU(val);
                      } else {
                          val->lru = LRU_CLOCK();
                      }
                  }
                  return val;
              } else {
                  return NULL;
              }
          }
          +

          updateLFU 这个其实个入口，调用了两个重要的方法

          +
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          /* Update LFU when an object is accessed.
           * Firstly, decrement the counter if the decrement time is reached.
           * Then logarithmically increment the counter, and update the access time. */
          void updateLFU(robj *val) {
              unsigned long counter = LFUDecrAndReturn(val);
              counter = LFULogIncr(counter);
              val->lru = (LFUGetTimeInMinutes()<<8) | counter;
          }
          +

          首先来看看LFUDecrAndReturn，这个方法的作用是根据上一次衰减时间和系统配置的 lfu-decay-time 参数来确定需要将 counter 减去多少

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          /* If the object decrement time is reached decrement the LFU counter but
           * do not update LFU fields of the object, we update the access time
           * and counter in an explicit way when the object is really accessed.
           * And we will times halve the counter according to the times of
           * elapsed time than server.lfu_decay_time.
           * Return the object frequency counter.
           *
           * This function is used in order to scan the dataset for the best object
           * to fit: as we check for the candidate, we incrementally decrement the
           * counter of the scanned objects if needed. */
          unsigned long LFUDecrAndReturn(robj *o) {
              // 右移 8 位，拿到上次衰减时间
              unsigned long ldt = o->lru >> 8;
              // 对 255 做与操作，拿到 counter 值
              unsigned long counter = o->lru & 255;
              // 根据lfu_decay_time来算出过了多少个衰减周期
              unsigned long num_periods = server.lfu_decay_time ? LFUTimeElapsed(ldt) / server.lfu_decay_time : 0;
              if (num_periods)
                  counter = (num_periods > counter) ? 0 : counter - num_periods;
              return counter;
          }
          +

          然后是加，调用了LFULogIncr

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          /* Logarithmically increment a counter. The greater is the current counter value
           * the less likely is that it gets really implemented. Saturate it at 255. */
          uint8_t LFULogIncr(uint8_t counter) {
              // 最大值就是 255，到顶了就不加了
              if (counter == 255) return 255;
              // 生成个随机小数
              double r = (double)rand()/RAND_MAX;
              // 减去个基础值，LFU_INIT_VAL = 5，防止刚进来就被逐出
              double baseval = counter - LFU_INIT_VAL;
              // 如果是小于 0，
              if (baseval < 0) baseval = 0;
              // 如果 baseval 是 0，那么 p 就是 1了，后面 counter 直接加一，如果不是的话，得看系统参数lfu_log_factor，这个越大，除出来的 p 越小，那么 counter++的可能性也越小，这样子就把前面的疑问给解决了，不是直接+1 的
              double p = 1.0/(baseval*server.lfu_log_factor+1);
              if (r < p) counter++;
              return counter;
          }
          +

          大概的变化速度可以参考

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          +--------+------------+------------+------------+------------+------------+
          | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |
          +--------+------------+------------+------------+------------+------------+
          | 0      | 104        | 255        | 255        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 1      | 18         | 49         | 255        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 10     | 10         | 18         | 142        | 255        | 255        |
          +--------+------------+------------+------------+------------+------------+
          | 100    | 8          | 11         | 49         | 143        | 255        |
          +--------+------------+------------+------------+------------+------------+
          +

          简而言之就是 lfu_log_factor 越大变化的越慢

          +

          总结

          总结一下，redis 实现了近似的 lru 淘汰策略，通过增加了淘汰 key 的池子(pool)，并且增大每次抽样的 key 的数量来将淘汰效果更进一步地接近于 lru，这是 lru 策略，但是对于前面举的一个例子，其实 lru 并不能保证 key 的淘汰就如我们预期，所以在后期又引入了 lfu 的策略，lfu的策略比较巧妙，复用了 redis 对象的 lru 字段，并且使用了factor 参数来控制计数器递增的速度，防止 8 位的计数器太早溢出。

          + + +
          + + + + + + +
          +
          +
          +
          + + + + + + +
          @@ -245,11 +388,11 @@ , - + , - + , @@ -645,122 +788,10 @@ - - - -
          - - - - - -
          -

          - - -

          - -
          - - - - - Posted on - - - - - - - - Edited on - - - - - - - In - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
          -
          - - - - -
          - - -

          限制下 docker 的 cpu 使用率

          这里我们开始玩一点有意思的，我们在容器里装下 vim 和 gcc，然后写这样一段 c 代码

          -
          1
          2
          3
          4
          5
          6
          7
          #include <stdio.h>
          int main(void)
          {
              int i = 0;
              for(;;) i++;
              return 0;
          }
          -

          就是一个最简单的死循环，然后在容器里跑起来

          -
          1
          2
          $ gcc 1.c 
          $ ./a.out
          -

          然后我们来看下系统资源占用（CPU）
          Xs562iawhHyMxeO
          上图是在容器里的，可以看到 cpu 已经 100%了
          然后看看容器外面的
          ecqH8XJ4k7rKhzu
          可以看到一个核的 cpu 也被占满了，因为是个双核的机器，并且代码是单线程的
          然后呢我们要做点啥
          因为已经在这个 ubuntu 容器中装了 vim 和 gcc，考虑到国内的网络，所以我们先把这个容器 commit 一下，

          -
          1
          docker commit -a "nick" -m "my ubuntu" f63c5607df06 my_ubuntu:v1
          -

          然后再运行起来

          -
          1
          docker run -it --cpus=0.1 my_ubuntu:v1 bash
          -


          我们的代码跟可执行文件都还在，要的就是这个效果，然后再运行一下

          结果是这个样子的，有点神奇是不，关键就在于 run 的时候的--cpus=0.1这个参数，它其实就是基于我前一篇说的 cgroup 技术，能将进程之间的cpu，内存等资源进行隔离

          -

          开始第一个 Dockerfile

          上一面为了复用那个我装了 vim 跟 gcc 的容器，我把它提交到了本地，使用了docker commit命令，有点类似于 git 的 commit，但是这个不是个很好的操作方式，需要手动介入，这里更推荐使用 Dockerfile 来构建镜像

          -
          1
          2
          3
          4
          5
          6
          7
          8
          From ubuntu:latest
          MAINTAINER Nicksxs "nicksxs@hotmail.com"
          RUN  sed -i s@/archive.ubuntu.com/@/mirrors.aliyun.com/@g /etc/apt/sources.list
          RUN apt-get clean
          RUN apt-get update && apt install -y nginx
          RUN echo 'Hi, i am in container' \
              > /usr/share/nginx/html/index.html
          EXPOSE 80
          -

          先解释下这是在干嘛，首先是这个From ubuntu:latest基于的 ubuntu 的最新版本的镜像，然后第二行是维护人的信息，第三四行么作为墙内人你懂的，把 ubuntu 的源换成阿里云的，不然就有的等了，然后就是装下 nginx，往默认的 nginx 的入口 html 文件里输入一行欢迎语，然后暴露 80 端口
          然后我们使用sudo docker build -t="nicksxs/static_web" .命令来基于这个 Dockerfile 构建我们自己的镜像，过程中是这样的


          可以看到图中，我的 Dockerfile 是 7 行，里面就执行了 7 步，并且每一步都有一个类似于容器 id 的层 id 出来，这里就是一个比较重要的东西，docker 在构建的时候其实是有这个层的概念，Dockerfile 里的每一行都会往上加一层，这里有还注意下命令后面的.，代表当前目录下会自行去寻找 Dockerfile 进行构建，构建完了之后我们再看下我们的本地镜像

          我们自己的镜像出现啦
          然后有个问题，如果这个构建中途报了错咋办呢，来试试看，我们把 nginx 改成随便的一个错误名，nginxx(不知道会不会运气好真的有这玩意)，再来 build 一把

          找不到 nginxx 包，是不是这个镜像就完全不能用呢，当然也不是，因为前面说到了，docker 是基于层去构建的，可以看到前面的 4 个 step 都没报错，那我们基于最后的成功步骤创建下容器看看
          也就是sudo docker run -t -i bd26f991b6c8 /bin/bash
          答案是可以的，只是没装成功 nginx

          还有一点注意到没，前面的几个 step 都有一句 Using cache，说明 docker 在构建镜像的时候是有缓存的，这也更能说明 docker 是基于层去构建镜像，同样的底包，同样的步骤，这些层是可以被复用的，这就是 docker 的构建缓存，当然我们也可以在 build 的时候加上--no-cache去把构建缓存禁用掉。

          - - -
          - - - - - - -
          -
          -
          -
          - - - - @@ -828,20 +859,20 @@
          - 70 + 71 posts
          - 81 + 83 categories
          - 113 + 114 tags
          @@ -866,7 +897,7 @@
          - +
          diff --git a/page/7/index.html b/page/7/index.html index 10a867c1aa..52d2ecaa34 100644 --- a/page/7/index.html +++ b/page/7/index.html @@ -203,6 +203,118 @@ +
          + + + + + +
          +

          + + +

          + +
          + + + + + Posted on + + + + + + + + Edited on + + + + + + + In + + + + , + + + + + + + + + + + Views: + + + + + + + + + Disqus: + + + + + + + + +
          +
          + + + + +
          + + +

          限制下 docker 的 cpu 使用率

          这里我们开始玩一点有意思的，我们在容器里装下 vim 和 gcc，然后写这样一段 c 代码

          +
          1
          2
          3
          4
          5
          6
          7
          #include <stdio.h>
          int main(void)
          {
              int i = 0;
              for(;;) i++;
              return 0;
          }
          +

          就是一个最简单的死循环，然后在容器里跑起来

          +
          1
          2
          $ gcc 1.c 
          $ ./a.out
          +

          然后我们来看下系统资源占用（CPU）
          Xs562iawhHyMxeO
          上图是在容器里的，可以看到 cpu 已经 100%了
          然后看看容器外面的
          ecqH8XJ4k7rKhzu
          可以看到一个核的 cpu 也被占满了，因为是个双核的机器，并且代码是单线程的
          然后呢我们要做点啥
          因为已经在这个 ubuntu 容器中装了 vim 和 gcc，考虑到国内的网络，所以我们先把这个容器 commit 一下，

          +
          1
          docker commit -a "nick" -m "my ubuntu" f63c5607df06 my_ubuntu:v1
          +

          然后再运行起来

          +
          1
          docker run -it --cpus=0.1 my_ubuntu:v1 bash
          +


          我们的代码跟可执行文件都还在，要的就是这个效果，然后再运行一下

          结果是这个样子的，有点神奇是不，关键就在于 run 的时候的--cpus=0.1这个参数，它其实就是基于我前一篇说的 cgroup 技术，能将进程之间的cpu，内存等资源进行隔离

          +

          开始第一个 Dockerfile

          上一面为了复用那个我装了 vim 跟 gcc 的容器，我把它提交到了本地，使用了docker commit命令，有点类似于 git 的 commit，但是这个不是个很好的操作方式，需要手动介入，这里更推荐使用 Dockerfile 来构建镜像

          +
          1
          2
          3
          4
          5
          6
          7
          8
          From ubuntu:latest
          MAINTAINER Nicksxs "nicksxs@hotmail.com"
          RUN  sed -i s@/archive.ubuntu.com/@/mirrors.aliyun.com/@g /etc/apt/sources.list
          RUN apt-get clean
          RUN apt-get update && apt install -y nginx
          RUN echo 'Hi, i am in container' \
              > /usr/share/nginx/html/index.html
          EXPOSE 80
          +

          先解释下这是在干嘛，首先是这个From ubuntu:latest基于的 ubuntu 的最新版本的镜像，然后第二行是维护人的信息，第三四行么作为墙内人你懂的，把 ubuntu 的源换成阿里云的，不然就有的等了，然后就是装下 nginx，往默认的 nginx 的入口 html 文件里输入一行欢迎语，然后暴露 80 端口
          然后我们使用sudo docker build -t="nicksxs/static_web" .命令来基于这个 Dockerfile 构建我们自己的镜像，过程中是这样的


          可以看到图中，我的 Dockerfile 是 7 行，里面就执行了 7 步，并且每一步都有一个类似于容器 id 的层 id 出来，这里就是一个比较重要的东西，docker 在构建的时候其实是有这个层的概念，Dockerfile 里的每一行都会往上加一层，这里有还注意下命令后面的.，代表当前目录下会自行去寻找 Dockerfile 进行构建，构建完了之后我们再看下我们的本地镜像

          我们自己的镜像出现啦
          然后有个问题，如果这个构建中途报了错咋办呢，来试试看，我们把 nginx 改成随便的一个错误名，nginxx(不知道会不会运气好真的有这玩意)，再来 build 一把

          找不到 nginxx 包，是不是这个镜像就完全不能用呢，当然也不是，因为前面说到了，docker 是基于层去构建的，可以看到前面的 4 个 step 都没报错，那我们基于最后的成功步骤创建下容器看看
          也就是sudo docker run -t -i bd26f991b6c8 /bin/bash
          答案是可以的，只是没装成功 nginx

          还有一点注意到没，前面的几个 step 都有一句 Using cache，说明 docker 在构建镜像的时候是有缓存的，这也更能说明 docker 是基于层去构建镜像，同样的底包，同样的步骤，这些层是可以被复用的，这就是 docker 的构建缓存，当然我们也可以在 build 的时候加上--no-cache去把构建缓存禁用掉。

          + + +
          + + + + + + +
          +
          +
          +
          + + + + + + +
          @@ -680,122 +792,10 @@ - - - -
          - - - - - -
          -

          - - -

          - -
          - - - - - Posted on - - - - - - - - - In - - - - , - - - - , - - - - , - - - - - - - - - - - Views: - - - - - - - - - Disqus: - - - - - - - - -
          -
          - - - - -
          - - -

          G1: The Garbage-First Collector, 垃圾回收优先的垃圾回收器，目标是用户多核 cpu 和大内存的机器，最大的特点就是可预测的停顿时间，官方给出的介绍是提供一个用户在大的堆内存情况下一个低延迟表现的解决方案，通常是 6GB 及以上的堆大小，有低于 0.5 秒稳定的可预测的停顿时间。

          -

          这里主要介绍这个比较新的垃圾回收器，在 G1 之前的垃圾回收器都是基于如下图的内存结构分布，有新生代，老年代和永久代（jdk8 之前），然后G1 往前的那些垃圾回收器都有个分代，比如 serial，parallel 等，一般有个应用的组合，最初的 serial 和 serial old，因为新生代和老年代的收集方式不太一样，新生代主要是标记复制，所以有 eden 跟两个 survival区，老年代一般用标记整理方式，而 G1 对这个不太一样。

          看一下 G1 的内存分布

          可以看到这有很大的不同，G1 通过将内存分成大小相等的 region，每个region是存在于一个连续的虚拟内存范围，对于某个 region 来说其角色是类似于原来的收集器的Eden、Survivor、Old Generation，这个具体在代码层面

          -
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          // We encode the value of the heap region type so the generation can be
           // determined quickly. The tag is split into two parts:
           //
           //   major type (young, old, humongous, archive)           : top N-1 bits
           //   minor type (eden / survivor, starts / cont hum, etc.) : bottom 1 bit
           //
           // If there's need to increase the number of minor types in the
           // future, we'll have to increase the size of the latter and hence
           // decrease the size of the former.
           //
           // 00000 0 [ 0] Free
           //
           // 00001 0 [ 2] Young Mask
           // 00001 0 [ 2] Eden
           // 00001 1 [ 3] Survivor
           //
           // 00010 0 [ 4] Humongous Mask
           // 00100 0 [ 8] Pinned Mask
           // 00110 0 [12] Starts Humongous
           // 00110 1 [13] Continues Humongous
           //
           // 01000 0 [16] Old Mask
           //
           // 10000 0 [32] Archive Mask
           // 11100 0 [56] Open Archive
           // 11100 1 [57] Closed Archive
           //
           typedef enum {
             FreeTag               = 0,

             YoungMask             = 2,
             EdenTag               = YoungMask,
             SurvTag               = YoungMask + 1,

             HumongousMask         = 4,
             PinnedMask            = 8,
             StartsHumongousTag    = HumongousMask | PinnedMask,
             ContinuesHumongousTag = HumongousMask | PinnedMask + 1,

             OldMask               = 16,
             OldTag                = OldMask,

             // Archive regions are regions with immutable content (i.e. not reclaimed, and
             // not allocated into during regular operation). They differ in the kind of references
             // allowed for the contained objects:
             // - Closed archive regions form a separate self-contained (closed) object graph
             // within the set of all of these regions. No references outside of closed
             // archive regions are allowed.
             // - Open archive regions have no restrictions on the references of their objects.
             // Objects within these regions are allowed to have references to objects
             // contained in any other kind of regions.
             ArchiveMask           = 32,
             OpenArchiveTag        = ArchiveMask | PinnedMask | OldMask,
             ClosedArchiveTag      = ArchiveMask | PinnedMask | OldMask + 1
           } Tag;
          - -

          hotspot/share/gc/g1/heapRegionType.hpp

          -

          当执行垃圾收集时，G1以类似于CMS收集器的方式运行。 G1执行并发全局标记阶段，以确定整个堆中对象的存活性。标记阶段完成后，G1知道哪些region是基本空的。它首先收集这些region，通常会产生大量的可用空间。这就是为什么这种垃圾收集方法称为“垃圾优先”的原因。顾名思义，G1将其收集和压缩活动集中在可能充满可回收对象（即垃圾）的堆区域。 G1使用暂停预测模型来满足用户定义的暂停时间目标，并根据指定的暂停时间目标选择要收集的区域数。

          -

          由G1标识为可回收的区域是使用撤离的方式(Evacuation)。 G1将对象从堆的一个或多个区域复制到堆上的单个区域，并在此过程中压缩并释放内存。撤离是在多处理器上并行执行的，以减少暂停时间并增加吞吐量。因此，对于每次垃圾收集，G1都在用户定义的暂停时间内连续工作以减少碎片。这是优于前面两种方法的。 CMS（并发标记扫描）垃圾收集器不进行压缩。 ParallelOld垃圾回收仅执行整个堆压缩，这导致相当长的暂停时间。

          -

          需要重点注意的是，G1不是实时收集器。它很有可能达到设定的暂停时间目标，但并非绝对确定。 G1根据先前收集的数据，估算在用户指定的目标时间内可以收集多少个区域。因此，收集器具有收集区域成本的合理准确的模型，并且收集器使用此模型来确定要收集哪些和多少个区域，同时保持在暂停时间目标之内。

          -

          注意：G1同时具有并发（与应用程序线程一起运行，例如优化，标记，清理）和并行（多线程，例如stw）阶段。Full GC仍然是单线程的，但是如果正确调优，您的应用程序应该可以避免Full GC。

          -

          在前面那篇中在代码层面简单的了解了这个可预测时间的过程，这也是 G1 的一大特点。

          - - -
          - - - - - - -
          -
          -
          -
          - - - - @@ -863,20 +863,20 @@
          - 70 + 71 posts
          - 81 + 83 categories
          - 113 + 114 tags
          @@ -901,7 +901,7 @@
          - +
          diff --git a/page/8/index.html b/page/8/index.html index e99128027d..bc2758da4f 100644 --- a/page/8/index.html +++ b/page/8/index.html @@ -204,7 +204,7 @@
          - +