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230 KiB
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class=tag-list-link href=/tags/Spring/ rel=tag>Spring</a><span class=tag-list-count>7</span><li class=tag-list-item><a class=tag-list-link href=/tags/Spring-Event/ rel=tag>Spring Event</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/SpringBoot/ rel=tag>SpringBoot</a><span class=tag-list-count>7</span><li class=tag-list-item><a class=tag-list-link href=/tags/Sql%E6%B3%A8%E5%85%A5/ rel=tag>Sql注入</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Stream/ rel=tag>Stream</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Synchronized/ rel=tag>Synchronized</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/Thread-dump/ rel=tag>Thread dump</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/ThreadLocal/ rel=tag>ThreadLocal</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/ThreadPool/ rel=tag>ThreadPool</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Tomcat/ rel=tag>Tomcat</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Trapping-Rain-Water/ rel=tag>Trapping Rain Water</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/WeakReference/ rel=tag>WeakReference</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Web/ rel=tag>Web</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Webhook/ rel=tag>Webhook</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/Windows/ rel=tag>Windows</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/WordPress/ rel=tag>WordPress</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/aqs/ rel=tag>aqs</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/await/ rel=tag>await</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/bloom-filter/ rel=tag>bloom filter</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/c/ rel=tag>c++</a><span class=tag-list-count>14</span><li class=tag-list-item><a class=tag-list-link href=/tags/cglib/ rel=tag>cglib</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/cgroup/ rel=tag>cgroup</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/cluster/ rel=tag>cluster</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/condition/ rel=tag>condition</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/dnsmasq/ rel=tag>dnsmasq</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/docker/ rel=tag>docker</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/dp/ rel=tag>dp</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/dubbo/ rel=tag>dubbo</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/echo/ rel=tag>echo</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/environment/ rel=tag>environment</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/gap-lock/ rel=tag>gap lock</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/gc/ rel=tag>gc</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/git/ rel=tag>git</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/grep/ rel=tag>grep</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/hadoop/ rel=tag>hadoop</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/headscale/ rel=tag>headscale</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/hexo/ rel=tag>hexo</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/icu4c/ rel=tag>icu4c</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/im/ rel=tag>im</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/is-not-null/ rel=tag>is not null</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/is-null/ rel=tag>is null</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/j-u-c/ rel=tag>j.u.c</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/java/ rel=tag>java</a><span class=tag-list-count>35</span><li class=tag-list-item><a class=tag-list-link href=/tags/jvm/ rel=tag>jvm</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/leetcode/ rel=tag>leetcode</a><span class=tag-list-count>40</span><li class=tag-list-item><a class=tag-list-link href=/tags/leetcode-155/ rel=tag>leetcode 155</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/linked-list/ rel=tag>linked list</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/linux/ rel=tag>linux</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/lock/ rel=tag>lock</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/mfc/ rel=tag>mfc</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/min-stack/ rel=tag>min stack</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/mq/ rel=tag>mq</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/mvcc/ rel=tag>mvcc</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/mysql/ rel=tag>mysql</a><span class=tag-list-count>6</span><li class=tag-list-item><a class=tag-list-link href=/tags/namespace/ rel=tag>namespace</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/nas/ rel=tag>nas</a><span class=tag-list-count>6</span><li class=tag-list-item><a class=tag-list-link href=/tags/next-key-lock/ rel=tag>next-key lock</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/nginx/ rel=tag>nginx</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/nullsfirst/ rel=tag>nullsfirst</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/openresty/ rel=tag>openresty</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/php/ rel=tag>php</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/powershell/ rel=tag>powershell</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/procedure/ rel=tag>procedure</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/python/ rel=tag>python</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/read-view/ rel=tag>read view</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/redis/ rel=tag>redis</a><span class=tag-list-count>12</span><li class=tag-list-item><a class=tag-list-link href=/tags/scp/ rel=tag>scp</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/signal/ rel=tag>signal</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/sort/ rel=tag>sort</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/spark/ rel=tag>spark</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/ssh/ rel=tag>ssh</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/stack/ rel=tag>stack</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/stream/ rel=tag>stream</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/string/ rel=tag>string</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/swoole/ rel=tag>swoole</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/top/ rel=tag>top</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/uname/ rel=tag>uname</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/unlock/ rel=tag>unlock</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8/ rel=tag>utf8</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4/ rel=tag>utf8mb4</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-0900-ai-ci/ rel=tag>utf8mb4_0900_ai_ci</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-general-ci/ rel=tag>utf8mb4_general_ci</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/utf8mb4-unicode-ci/ rel=tag>utf8mb4_unicode_ci</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/value/ rel=tag>value</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/websocket/ rel=tag>websocket</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/windows/ rel=tag>windows</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/wsl/ rel=tag>wsl</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/zookeeper/ rel=tag>zookeeper</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/zsh/ rel=tag>zsh</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%89%E9%98%B6%E6%AE%B5%E6%8F%90%E4%BA%A4/ rel=tag>三阶段提交</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%8D%E5%8F%AF%E5%8F%98%E5%BC%95%E7%94%A8/ rel=tag>不可变引用</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%9C%E4%BA%AC%E5%A5%A5%E8%BF%90%E4%BC%9A/ rel=tag>东京奥运会</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%A4%E9%98%B6%E6%AE%B5%E6%8F%90%E4%BA%A4/ rel=tag>两阶段提交</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%AD%E5%B1%B1%E8%B7%AF/ rel=tag>中山路</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%AD%E5%BA%8F/ rel=tag>中序</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%AD%E9%97%B4%E4%BB%B6/ rel=tag>中间件</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B8%BE%E9%87%8D/ rel=tag>举重</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%B9%92%E4%B9%93%E7%90%83/ rel=tag>乒乓球</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%BA%8B%E5%8A%A1/ rel=tag>事务</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%BA%8C%E5%8F%89%E6%A0%91/ rel=tag>二叉树</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%BA%92%E6%96%A5%E9%94%81/ rel=tag>互斥锁</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%BB%A3%E7%A0%81%E9%A2%98%E8%A7%A3/ rel=tag>代码题解</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E4%BF%AE%E7%94%B5%E8%84%91%E7%9A%84/ rel=tag>修电脑的</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%81%8F%E5%90%91%E9%94%81/ rel=tag>偏向锁</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%81%A5%E5%BA%B7%E7%A0%81/ rel=tag>健康码</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%85%AC%E4%BA%A4/ rel=tag>公交</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%85%AC%E4%BA%A4%E8%BD%A6/ rel=tag>公交车</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%86%85%E5%AD%98%E5%88%86%E5%B8%83/ rel=tag>内存分布</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%86%85%E5%AD%98%E6%B3%84%E6%BC%8F/ rel=tag>内存泄漏</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%87%86%E5%A4%87/ rel=tag>准备</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%87%8F%E8%82%A5/ rel=tag>减肥</a><span class=tag-list-count>7</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%88%86%E5%B8%83%E5%BC%8F%E4%BA%8B%E5%8A%A1/ rel=tag>分布式事务</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%88%86%E5%B8%83%E5%BC%8F%E9%94%81/ rel=tag>分布式锁</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%88%87%E7%89%87/ rel=tag>切片</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%88%9D%E5%A7%8B%E5%8C%96/ rel=tag>初始化</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%89%8A%E5%B3%B0%E5%A1%AB%E8%B0%B7/ rel=tag>削峰填谷</a><span class=tag-list-count>4</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%89%8D%E5%BA%8F/ rel=tag>前序</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8A%A0%E5%A1%9E/ rel=tag>加塞</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8A%A0%E8%BD%BD/ rel=tag>加载</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8D%95%E4%BE%8B/ rel=tag>单例</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8D%9A%E5%AE%A2%EF%BC%8C%E6%96%87%E7%AB%A0/ rel=tag>博客，文章</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8E%A6%E9%97%A8/ rel=tag>厦门</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8F%8C%E4%BA%B2%E5%A7%94%E6%B4%BE/ rel=tag>双亲委派</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8F%91%E8%A1%8C%E7%89%88/ rel=tag>发行版</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8F%A3%E7%BD%A9/ rel=tag>口罩</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%8F%AF%E5%8F%98%E5%BC%95%E7%94%A8/ rel=tag>可变引用</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%90%90%E6%A7%BD/ rel=tag>吐槽</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%9B%A4%E7%89%A9%E8%B5%84/ rel=tag>囤物资</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%9E%83%E5%9C%BE%E5%9B%9E%E6%94%B6/ rel=tag>垃圾回收</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%9F%BA%E7%A1%80%E8%AE%BE%E6%96%BD/ rel=tag>基础设施</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%A4%A7%E6%89%AB%E9%99%A4/ rel=tag>大扫除</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E5%AD%97%E7%AC%A6%E9%9B%86/ rel=tag>字符集</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link 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href=/tags/%E6%8D%A2%E8%BD%A6%E7%89%8C/ rel=tag>换车牌</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%8E%92%E5%BA%8F/ rel=tag>排序</a><span class=tag-list-count>2</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%8E%A5%E9%9B%A8%E6%B0%B4/ rel=tag>接雨水</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%95%B0%E6%8D%AE%E6%BA%90%E5%8A%A8%E6%80%81%E5%88%87%E6%8D%A2/ rel=tag>数据源动态切换</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/ rel=tag>数据结构</a><span class=tag-list-count>11</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%96%B0%E8%AF%AD%E8%A8%80/ rel=tag>新语言</a><span class=tag-list-count>3</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E6%97%85%E6%B8%B8/ rel=tag>旅游</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link 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href=/tags/%E7%B1%BB%E5%8A%A0%E8%BD%BD/ rel=tag>类加载</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%B3%9F%E5%BF%83%E4%BA%8B/ rel=tag>糟心事</a><span class=tag-list-count>5</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%B4%A2%E5%BC%95/ rel=tag>索引</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BA%BF%E7%A8%8B%E6%B1%A0/ rel=tag>线程池</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98/ rel=tag>缓存</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/ rel=tag>缓存击穿</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link href=/tags/%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/ rel=tag>缓存穿透</a><span class=tag-list-count>1</span><li class=tag-list-item><a class=tag-list-link 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title=https://covermusic.cn>69伙伴</a></ul></div></div></aside></div><div class="main-inner index posts-expand"><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article><link href=https://nicksxs.me/2021/02/21/AQS-%E4%B9%8B-Condition-%E6%B5%85%E6%9E%90%E7%AC%94%E8%AE%B0/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="undefined | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h2 itemprop="name headline" class=post-title><a class=post-title-link href=/2021/02/21/AQS-%E4%B9%8B-Condition-%E6%B5%85%E6%9E%90%E7%AC%94%E8%AE%B0/ itemprop=url>AQS篇二 之 Condition 浅析笔记</a></h2><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2021-02-21 21:27:06" datetime=2021-02-21T21:27:06+08:00>2021-02-21</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar-check"></i> </span><span class=post-meta-item-text>更新于</span> <time title="修改时间：2022-06-11 22:45:11" datetime=2022-06-11T22:45:11+08:00 itemprop=dateModified>2022-06-11</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/%E5%B9%B6%E5%8F%91/ itemprop=url rel=index><span itemprop=name>并发</span></a> </span></span><span class="post-meta-item leancloud_visitors" data-flag-title="AQS篇二 之 Condition 浅析笔记" id=/2021/02/21/AQS-%E4%B9%8B-Condition-%E6%B5%85%E6%9E%90%E7%AC%94%E8%AE%B0/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-comment"></i> </span><span class=post-meta-item-text>Disqus：</span> <a href=/2021/02/21/AQS-%E4%B9%8B-Condition-%E6%B5%85%E6%9E%90%E7%AC%94%E8%AE%B0/#disqus_thread itemprop=discussionUrl title=disqus><span class="post-comments-count disqus-comment-count" data-disqus-identifier=2021/02/21/AQS-之-Condition-浅析笔记/ itemprop=commentCount></span></a></span></div></div></header><div class=post-body itemprop=articleBody><p>Condition也是 AQS 中很重要的一块内容，可以先看段示例代码，这段代码应该来自于Doug Lea大大，可以在 javadoc 中的 <a href=https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Condition.html rel=noopener target=_blank>condition</a> 部分找到，其实大大原来写过基于 <code>synchronized</code> 实现的，后面我也贴下代码<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>concurrent<span class="token punctuation">.</span>locks<span class="token punctuation">.</span></span><span class="token class-name">Condition</span></span><span class="token punctuation">;</span>
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<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>concurrent<span class="token punctuation">.</span>locks<span class="token punctuation">.</span></span><span class="token class-name">Lock</span></span><span class="token punctuation">;</span>
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<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>concurrent<span class="token punctuation">.</span>locks<span class="token punctuation">.</span></span><span class="token class-name">ReentrantLock</span></span><span class="token punctuation">;</span>
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<span class="token keyword">class</span> <span class="token class-name">BoundedBuffer</span> <span class="token punctuation">{</span>
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<span class="token keyword">final</span> <span class="token class-name">Lock</span> lock <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ReentrantLock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// condition 依赖于 lock 来产生</span>
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<span class="token keyword">final</span> <span class="token class-name">Condition</span> notFull <span class="token operator">=</span> lock<span class="token punctuation">.</span><span class="token function">newCondition</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">final</span> <span class="token class-name">Condition</span> notEmpty <span class="token operator">=</span> lock<span class="token punctuation">.</span><span class="token function">newCondition</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 对象池子，put 跟 take 的就是这里的</span>
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<span class="token keyword">final</span> <span class="token class-name">Object</span><span class="token punctuation">[</span><span class="token punctuation">]</span> items <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Object</span><span class="token punctuation">[</span><span class="token number">100</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
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<span class="token keyword">int</span> putptr<span class="token punctuation">,</span> takeptr<span class="token punctuation">,</span> count<span class="token punctuation">;</span>
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<span class="token comment">// 生产</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">put</span><span class="token punctuation">(</span><span class="token class-name">Object</span> x<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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<span class="token comment">// 这里也说明了，需要先拥有锁</span>
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lock<span class="token punctuation">.</span><span class="token function">lock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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<span class="token keyword">while</span> <span class="token punctuation">(</span>count <span class="token operator">==</span> items<span class="token punctuation">.</span>length<span class="token punctuation">)</span>
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notFull<span class="token punctuation">.</span><span class="token function">await</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 队列已满，等待，直到 not full 才能继续生产</span>
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items<span class="token punctuation">[</span>putptr<span class="token punctuation">]</span> <span class="token operator">=</span> x<span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">++</span>putptr <span class="token operator">==</span> items<span class="token punctuation">.</span>length<span class="token punctuation">)</span> putptr <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token operator">++</span>count<span class="token punctuation">;</span>
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notEmpty<span class="token punctuation">.</span><span class="token function">signal</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 生产成功，队列已经 not empty 了，发个通知出去</span>
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<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
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lock<span class="token punctuation">.</span><span class="token function">unlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 消费</span>
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<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">take</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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lock<span class="token punctuation">.</span><span class="token function">lock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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<span class="token keyword">while</span> <span class="token punctuation">(</span>count <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span>
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notEmpty<span class="token punctuation">.</span><span class="token function">await</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 队列为空，等待，直到队列 not empty，才能继续消费</span>
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<span class="token class-name">Object</span> x <span class="token operator">=</span> items<span class="token punctuation">[</span>takeptr<span class="token punctuation">]</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">++</span>takeptr <span class="token operator">==</span> items<span class="token punctuation">.</span>length<span class="token punctuation">)</span> takeptr <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token operator">--</span>count<span class="token punctuation">;</span>
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notFull<span class="token punctuation">.</span><span class="token function">signal</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 被我消费掉一个，队列 not full 了，发个通知出去</span>
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<span class="token keyword">return</span> x<span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
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lock<span class="token punctuation">.</span><span class="token function">unlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>介绍下 Condition 的结构<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">ConditionObject</span> <span class="token keyword">implements</span> <span class="token class-name">Condition</span><span class="token punctuation">,</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span>Serializable</span> <span class="token punctuation">{</span>
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<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">long</span> serialVersionUID <span class="token operator">=</span> <span class="token number">1173984872572414699L</span><span class="token punctuation">;</span>
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<span class="token comment">/** First node of condition queue. */</span>
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<span class="token keyword">private</span> <span class="token keyword">transient</span> <span class="token class-name">Node</span> firstWaiter<span class="token punctuation">;</span>
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<span class="token comment">/** Last node of condition queue. */</span>
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<span class="token keyword">private</span> <span class="token keyword">transient</span> <span class="token class-name">Node</span> lastWaiter<span class="token punctuation">;</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>主要的就这么点，而且也复用了 AQS 阻塞队列或者大大叫 <code>lock queue</code>中同样的 Node 节点，只不过它没有使用其中的双向队列，也就是prev 和 next，而是在 Node 中的 nextWaiter，所以只是个单向的队列，没使用 next 其实还有个用处，后面会提到，看下结构的示意图<br><img data-src=https://img.nicksxs.com/uPic/Ss9oFX.png><br>然后主要是看两个方法，<code>await</code> 和 <code>signal</code>,<br>先来看下 await<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
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* Implements interruptible condition wait.
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* <ol>
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* <li> If current thread is interrupted, throw InterruptedException.
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* <li> Save lock state returned by {@link #getState}.
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* <li> Invoke {@link #release} with saved state as argument,
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* throwing IllegalMonitorStateException if it fails.
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* <li> Block until signalled or interrupted.
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* <li> Reacquire by invoking specialized version of
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* {@link #acquire} with saved state as argument.
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* <li> If interrupted while blocked in step 4, throw InterruptedException.
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* </ol>
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*/</span>
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<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">void</span> <span class="token function">await</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">interrupted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
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<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">InterruptedException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 将当前节点包装成一个 condition waiter node 节点</span>
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<span class="token class-name">Node</span> node <span class="token operator">=</span> <span class="token function">addConditionWaiter</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 完全释放占有的锁，这里需要是占有锁的线程</span>
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<span class="token keyword">int</span> savedState <span class="token operator">=</span> <span class="token function">fullyRelease</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">int</span> interruptMode <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token comment">// 判断下是否在阻塞队列中，因为有可能被其他节点从等待队列移动到阻塞队列</span>
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<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">isOnSyncQueue</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment">// park等待，等待被唤醒</span>
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<span class="token class-name">LockSupport</span><span class="token punctuation">.</span><span class="token function">park</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>interruptMode <span class="token operator">=</span> <span class="token function">checkInterruptWhileWaiting</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span>
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<span class="token keyword">break</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 被唤醒后进入阻塞队列，等待获取锁，这里继续用了fullyRelease返回的 state</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">acquireQueued</span><span class="token punctuation">(</span>node<span class="token punctuation">,</span> savedState<span class="token punctuation">)</span> <span class="token operator">&&</span> interruptMode <span class="token operator">!=</span> <span class="token constant">THROW_IE</span><span class="token punctuation">)</span>
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interruptMode <span class="token operator">=</span> <span class="token constant">REINTERRUPT</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>nextWaiter <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token comment">// clean up if cancelled</span>
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<span class="token function">unlinkCancelledWaiters</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>interruptMode <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span>
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<span class="token function">reportInterruptAfterWait</span><span class="token punctuation">(</span>interruptMode<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>添加条件队列节点<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
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* Adds a new waiter to wait queue.
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* @return its new wait node
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*/</span>
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<span class="token keyword">private</span> <span class="token class-name">Node</span> <span class="token function">addConditionWaiter</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token class-name">Node</span> t <span class="token operator">=</span> lastWaiter<span class="token punctuation">;</span>
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<span class="token comment">// If lastWaiter is cancelled, clean out.</span>
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<span class="token comment">// 如果节点已经不是 CONDITION 状态了，表示已经取消了</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>t <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">&&</span> t<span class="token punctuation">.</span>waitStatus <span class="token operator">!=</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CONDITION</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment">// 把等待队列中取消的节点清理出去</span>
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<span class="token function">unlinkCancelledWaiters</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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t <span class="token operator">=</span> lastWaiter<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 把当前线程包装成waitStatus=CONDITION 的节点</span>
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<span class="token class-name">Node</span> node <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Node</span><span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CONDITION</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 没有 lastWaiter 节点，直接是 firstWaiter</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>t <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
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firstWaiter <span class="token operator">=</span> node<span class="token punctuation">;</span>
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<span class="token keyword">else</span>
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<span class="token comment">// 不然就接在 lastWaiter 后面</span>
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t<span class="token punctuation">.</span>nextWaiter <span class="token operator">=</span> node<span class="token punctuation">;</span>
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<span class="token comment">// 当前节点就会变成新的 lastWaiter</span>
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lastWaiter <span class="token operator">=</span> node<span class="token punctuation">;</span>
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<span class="token keyword">return</span> node<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>清理取消的节点<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Unlinks cancelled waiter nodes from condition queue.
|
|
* Called only while holding lock. This is called when
|
|
* cancellation occurred during condition wait, and upon
|
|
* insertion of a new waiter when lastWaiter is seen to have
|
|
* been cancelled. This method is needed to avoid garbage
|
|
* retention in the absence of signals. So even though it may
|
|
* require a full traversal, it comes into play only when
|
|
* timeouts or cancellations occur in the absence of
|
|
* signals. It traverses all nodes rather than stopping at a
|
|
* particular target to unlink all pointers to garbage nodes
|
|
* without requiring many re-traversals during cancellation
|
|
* storms.
|
|
*/</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">unlinkCancelledWaiters</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token class-name">Node</span> t <span class="token operator">=</span> firstWaiter<span class="token punctuation">;</span>
|
|
<span class="token class-name">Node</span> trail <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 循环遍历单向链表的节点，如果状态不是 CONDITION 就清出去</span>
|
|
<span class="token keyword">while</span> <span class="token punctuation">(</span>t <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token class-name">Node</span> next <span class="token operator">=</span> t<span class="token punctuation">.</span>nextWaiter<span class="token punctuation">;</span>
|
|
<span class="token comment">// 循环链表操作，清掉取消的节点</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>t<span class="token punctuation">.</span>waitStatus <span class="token operator">!=</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CONDITION</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
t<span class="token punctuation">.</span>nextWaiter <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>trail <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
firstWaiter <span class="token operator">=</span> next<span class="token punctuation">;</span>
|
|
<span class="token keyword">else</span>
|
|
trail<span class="token punctuation">.</span>nextWaiter <span class="token operator">=</span> next<span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>next <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
lastWaiter <span class="token operator">=</span> trail<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token keyword">else</span>
|
|
trail <span class="token operator">=</span> t<span class="token punctuation">;</span>
|
|
t <span class="token operator">=</span> next<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>完全释放锁<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Invokes release with current state value; returns saved state.
|
|
* Cancels node and throws exception on failure.
|
|
* @param node the condition node for this wait
|
|
* @return previous sync state
|
|
*/</span>
|
|
<span class="token keyword">final</span> <span class="token keyword">int</span> <span class="token function">fullyRelease</span><span class="token punctuation">(</span><span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">boolean</span> failed <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">try</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 获取下当前的 state 值，因为是可重入的，所以这个值要保存下来</span>
|
|
<span class="token keyword">int</span> savedState <span class="token operator">=</span> <span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 这里还包含比较多操作，不过跟前面分析 AQS 的释放比较类似，不深入了</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">release</span><span class="token punctuation">(</span>savedState<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
failed <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 返回这个值</span>
|
|
<span class="token keyword">return</span> savedState<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalMonitorStateException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>failed<span class="token punctuation">)</span>
|
|
node<span class="token punctuation">.</span>waitStatus <span class="token operator">=</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CANCELLED</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>判断是否在阻塞队列中<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Returns true if a node, always one that was initially placed on
|
|
* a condition queue, is now waiting to reacquire on sync queue.
|
|
* @param node the node
|
|
* @return true if is reacquiring
|
|
*/</span>
|
|
<span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">isOnSyncQueue</span><span class="token punctuation">(</span><span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 如果waitStatus 是 CONDITION 或者没有 prev 前置节点肯定就不在</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>waitStatus <span class="token operator">==</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CONDITION</span> <span class="token operator">||</span> node<span class="token punctuation">.</span>prev <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 这里就是我前面提到的 next 的作用</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>next <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token comment">// If has successor, it must be on queue</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 从 tail 开始找，是否在阻塞队列中</span>
|
|
<span class="token comment">/*
|
|
* node.prev can be non-null, but not yet on queue because
|
|
* the CAS to place it on queue can fail. So we have to
|
|
* traverse from tail to make sure it actually made it. It
|
|
* will always be near the tail in calls to this method, and
|
|
* unless the CAS failed (which is unlikely), it will be
|
|
* there, so we hardly ever traverse much.
|
|
*/</span>
|
|
<span class="token keyword">return</span> <span class="token function">findNodeFromTail</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token comment">/**
|
|
* Returns true if node is on sync queue by searching backwards from tail.
|
|
* Called only when needed by isOnSyncQueue.
|
|
* @return true if present
|
|
*/</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">boolean</span> <span class="token function">findNodeFromTail</span><span class="token punctuation">(</span><span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token class-name">Node</span> t <span class="token operator">=</span> tail<span class="token punctuation">;</span>
|
|
<span class="token comment">// 从 tail 开始，从后往前找</span>
|
|
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token punctuation">;</span><span class="token punctuation">;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>t <span class="token operator">==</span> node<span class="token punctuation">)</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>t <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
t <span class="token operator">=</span> t<span class="token punctuation">.</span>prev<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>await 的逻辑差不多就是这样子，主要的就是把自己包成一个 Node 节点，waitStatus 的状态是 CONDITION，挂在等待队列的最后，然后完全释放锁，park 等待<h2 id=signal><a class=headerlink href=#signal title=signal></a>signal</h2><pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Moves the longest-waiting thread, if one exists, from the
|
|
* wait queue for this condition to the wait queue for the
|
|
* owning lock.
|
|
*
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/</span>
|
|
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">void</span> <span class="token function">signal</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">isHeldExclusively</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalMonitorStateException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// firstWaiter 肯定是最早开始等待的</span>
|
|
<span class="token class-name">Node</span> first <span class="token operator">=</span> firstWaiter<span class="token punctuation">;</span>
|
|
<span class="token comment">// 如果不为空就唤醒</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>first <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
<span class="token function">doSignal</span><span class="token punctuation">(</span>first<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token comment">/**
|
|
* Removes and transfers nodes until hit non-cancelled one or
|
|
* null. Split out from signal in part to encourage compilers
|
|
* to inline the case of no waiters.
|
|
* @param first (non-null) the first node on condition queue
|
|
*/</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">doSignal</span><span class="token punctuation">(</span><span class="token class-name">Node</span> first<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">do</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 因为要去唤醒 first 节点了，firstWaiter 需要再从后面找一个</span>
|
|
<span class="token comment">// 并且判断是否为空，如果是空的话就直接可以把 lastWaiter 设置成空了</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token punctuation">(</span>firstWaiter <span class="token operator">=</span> first<span class="token punctuation">.</span>nextWaiter<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
lastWaiter <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// first 不需要继续保存后面的 waiter 了，因为 firstWaiter 已经是 first 的后置节点了</span>
|
|
first<span class="token punctuation">.</span>nextWaiter <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 如果 first 节点转移不成功，并且 firstWaiter 节点不为空，则继续进入循环</span>
|
|
<span class="token punctuation">}</span> <span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">transferForSignal</span><span class="token punctuation">(</span>first<span class="token punctuation">)</span> <span class="token operator">&&</span>
|
|
<span class="token punctuation">(</span>first <span class="token operator">=</span> firstWaiter<span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token comment">/**
|
|
* Transfers a node from a condition queue onto sync queue.
|
|
* Returns true if successful.
|
|
* @param node the node
|
|
* @return true if successfully transferred (else the node was
|
|
* cancelled before signal)
|
|
*/</span>
|
|
<span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">transferForSignal</span><span class="token punctuation">(</span><span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">/*
|
|
* If cannot change waitStatus, the node has been cancelled.
|
|
*/</span>
|
|
<span class="token comment">// 如果状态已经不是 CONDITION 就不会设置成功，返回 false</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">compareAndSetWaitStatus</span><span class="token punctuation">(</span>node<span class="token punctuation">,</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">CONDITION</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
<span class="token comment">/*
|
|
* Splice onto queue and try to set waitStatus of predecessor to
|
|
* indicate that thread is (probably) waiting. If cancelled or
|
|
* attempt to set waitStatus fails, wake up to resync (in which
|
|
* case the waitStatus can be transiently and harmlessly wrong).
|
|
*/</span>
|
|
<span class="token comment">// 调用跟aqs 第一篇中一样的 enq 方法进入阻塞队列，返回入队后的前一节点</span>
|
|
<span class="token class-name">Node</span> p <span class="token operator">=</span> <span class="token function">enq</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">int</span> ws <span class="token operator">=</span> p<span class="token punctuation">.</span>waitStatus<span class="token punctuation">;</span>
|
|
<span class="token comment">// 将前置节点状态设置成SIGNAL，表示后面有节点在等了</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>ws <span class="token operator">></span> <span class="token number">0</span> <span class="token operator">||</span> <span class="token operator">!</span><span class="token function">compareAndSetWaitStatus</span><span class="token punctuation">(</span>p<span class="token punctuation">,</span> ws<span class="token punctuation">,</span> <span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">SIGNAL</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
|
<span class="token class-name">LockSupport</span><span class="token punctuation">.</span><span class="token function">unpark</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>thread<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 返回 true，上一个方法的循环就退出了</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>这里其实就是把 condition 等待队列的第一个未取消的节点入队到阻塞队列去争锁<h2 id=附录><a class=headerlink href=#附录 title=附录></a>附录</h2><p><code>synchronized</code> 版的 BoundedBuffer<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/*
|
|
File: BoundedBuffer.java
|
|
|
|
Originally written by Doug Lea and released into the public domain.
|
|
This may be used for any purposes whatsoever without acknowledgment.
|
|
Thanks for the assistance and support of Sun Microsystems Labs,
|
|
and everyone contributing, testing, and using this code.
|
|
|
|
History:
|
|
Date Who What
|
|
11Jun1998 dl Create public version
|
|
17Jul1998 dl Simplified by eliminating wait counts
|
|
25aug1998 dl added peek
|
|
5May1999 dl replace % with conditional (slightly faster)
|
|
*/</span>
|
|
|
|
<span class="token keyword">package</span> <span class="token constant">EDU</span><span class="token punctuation">.</span>oswego<span class="token punctuation">.</span>cs<span class="token punctuation">.</span>dl<span class="token punctuation">.</span>util<span class="token punctuation">.</span>concurrent<span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">/**
|
|
* Efficient array-based bounded buffer class.
|
|
* Adapted from CPJ, chapter 8, which describes design.
|
|
* <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p>
|
|
**/</span>
|
|
|
|
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">BoundedBuffer</span> <span class="token keyword">implements</span> <span class="token class-name">BoundedChannel</span> <span class="token punctuation">{</span>
|
|
|
|
<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token class-name">Object</span><span class="token punctuation">[</span><span class="token punctuation">]</span> array_<span class="token punctuation">;</span> <span class="token comment">// the elements</span>
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<span class="token keyword">protected</span> <span class="token keyword">int</span> takePtr_ <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> <span class="token comment">// circular indices</span>
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<span class="token keyword">protected</span> <span class="token keyword">int</span> putPtr_ <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token keyword">protected</span> <span class="token keyword">int</span> usedSlots_ <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> <span class="token comment">// length</span>
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<span class="token keyword">protected</span> <span class="token keyword">int</span> emptySlots_<span class="token punctuation">;</span> <span class="token comment">// capacity - length</span>
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<span class="token comment">/**
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* Helper monitor to handle puts.
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**/</span>
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<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token class-name">Object</span> putMonitor_ <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Object</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">/**
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* Create a BoundedBuffer with the given capacity.
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* @exception IllegalArgumentException if capacity less or equal to zero
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**/</span>
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<span class="token keyword">public</span> <span class="token class-name">BoundedBuffer</span><span class="token punctuation">(</span><span class="token keyword">int</span> capacity<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IllegalArgumentException</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>capacity <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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array_ <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Object</span><span class="token punctuation">[</span>capacity<span class="token punctuation">]</span><span class="token punctuation">;</span>
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emptySlots_ <span class="token operator">=</span> capacity<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">/**
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* Create a buffer with the current default capacity
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**/</span>
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<span class="token keyword">public</span> <span class="token class-name">BoundedBuffer</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">this</span><span class="token punctuation">(</span><span class="token class-name">DefaultChannelCapacity</span><span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">/**
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* Return the number of elements in the buffer.
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* This is only a snapshot value, that may change
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* immediately after returning.
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**/</span>
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<span class="token keyword">public</span> <span class="token keyword">synchronized</span> <span class="token keyword">int</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> usedSlots_<span class="token punctuation">;</span> <span class="token punctuation">}</span>
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<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">capacity</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> array_<span class="token punctuation">.</span>length<span class="token punctuation">;</span> <span class="token punctuation">}</span>
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<span class="token keyword">protected</span> <span class="token keyword">void</span> <span class="token function">incEmptySlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">synchronized</span><span class="token punctuation">(</span>putMonitor_<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token operator">++</span>emptySlots_<span class="token punctuation">;</span>
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putMonitor_<span class="token punctuation">.</span><span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">protected</span> <span class="token keyword">synchronized</span> <span class="token keyword">void</span> <span class="token function">incUsedSlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token operator">++</span>usedSlots_<span class="token punctuation">;</span>
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<span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token keyword">void</span> <span class="token function">insert</span><span class="token punctuation">(</span><span class="token class-name">Object</span> x<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// mechanics of put</span>
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<span class="token operator">--</span>emptySlots_<span class="token punctuation">;</span>
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array_<span class="token punctuation">[</span>putPtr_<span class="token punctuation">]</span> <span class="token operator">=</span> x<span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">++</span>putPtr_ <span class="token operator">>=</span> array_<span class="token punctuation">.</span>length<span class="token punctuation">)</span> putPtr_ <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token class-name">Object</span> <span class="token function">extract</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// mechanics of take</span>
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<span class="token operator">--</span>usedSlots_<span class="token punctuation">;</span>
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<span class="token class-name">Object</span> old <span class="token operator">=</span> array_<span class="token punctuation">[</span>takePtr_<span class="token punctuation">]</span><span class="token punctuation">;</span>
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array_<span class="token punctuation">[</span>takePtr_<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">++</span>takePtr_ <span class="token operator">>=</span> array_<span class="token punctuation">.</span>length<span class="token punctuation">)</span> takePtr_ <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> old<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">peek</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">synchronized</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>usedSlots_ <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span>
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<span class="token keyword">return</span> array_<span class="token punctuation">[</span>takePtr_<span class="token punctuation">]</span><span class="token punctuation">;</span>
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<span class="token keyword">else</span>
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<span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">put</span><span class="token punctuation">(</span><span class="token class-name">Object</span> x<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>x <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">interrupted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">InterruptedException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">synchronized</span><span class="token punctuation">(</span>putMonitor_<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">while</span> <span class="token punctuation">(</span>emptySlots_ <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span> putMonitor_<span class="token punctuation">.</span><span class="token function">wait</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
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<span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> ex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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putMonitor_<span class="token punctuation">.</span><span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">throw</span> ex<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token function">insert</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token function">incUsedSlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">public</span> <span class="token keyword">boolean</span> <span class="token function">offer</span><span class="token punctuation">(</span><span class="token class-name">Object</span> x<span class="token punctuation">,</span> <span class="token keyword">long</span> msecs<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>x <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">interrupted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">InterruptedException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">synchronized</span><span class="token punctuation">(</span>putMonitor_<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token punctuation">(</span>msecs <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token operator">?</span> <span class="token number">0</span> <span class="token operator">:</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token keyword">long</span> waitTime <span class="token operator">=</span> msecs<span class="token punctuation">;</span>
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|
<span class="token keyword">while</span> <span class="token punctuation">(</span>emptySlots_ <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span>waitTime <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
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|
<span class="token keyword">try</span> <span class="token punctuation">{</span> putMonitor_<span class="token punctuation">.</span><span class="token function">wait</span><span class="token punctuation">(</span>waitTime<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
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|
<span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> ex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
putMonitor_<span class="token punctuation">.</span><span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">throw</span> ex<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
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|
waitTime <span class="token operator">=</span> msecs <span class="token operator">-</span> <span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token punctuation">}</span>
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|
<span class="token function">insert</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
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|
<span class="token function">incUsedSlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
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|
<span class="token punctuation">}</span>
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|
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<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">take</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">interrupted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">InterruptedException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token class-name">Object</span> old <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">synchronized</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">while</span> <span class="token punctuation">(</span>usedSlots_ <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
<span class="token keyword">try</span> <span class="token punctuation">{</span> <span class="token function">wait</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
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|
<span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> ex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">throw</span> ex<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span>
|
|
old <span class="token operator">=</span> <span class="token function">extract</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token function">incEmptySlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> old<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
|
|
<span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">poll</span><span class="token punctuation">(</span><span class="token keyword">long</span> msecs<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">InterruptedException</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">interrupted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">InterruptedException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token class-name">Object</span> old <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">synchronized</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token punctuation">(</span>msecs <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token operator">?</span> <span class="token number">0</span> <span class="token operator">:</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">long</span> waitTime <span class="token operator">=</span> msecs<span class="token punctuation">;</span>
|
|
|
|
<span class="token keyword">while</span> <span class="token punctuation">(</span>usedSlots_ <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>waitTime <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">try</span> <span class="token punctuation">{</span> <span class="token function">wait</span><span class="token punctuation">(</span>waitTime<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
|
|
<span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> ex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token function">notify</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">throw</span> ex<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
waitTime <span class="token operator">=</span> msecs <span class="token operator">-</span> <span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
|
|
<span class="token punctuation">}</span>
|
|
old <span class="token operator">=</span> <span class="token function">extract</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token function">incEmptySlots</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> old<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
|
|
<span class="token punctuation">}</span>
|
|
<span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre></div><footer class=post-footer><div class=post-eof></div></footer></article></div><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article><link href=https://nicksxs.me/2021/02/14/AQS%E7%AF%87%E4%B8%80/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="undefined | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h2 itemprop="name headline" class=post-title><a class=post-title-link href=/2021/02/14/AQS%E7%AF%87%E4%B8%80/ itemprop=url>AQS篇一</a></h2><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2021-02-14 22:51:54" datetime=2021-02-14T22:51:54+08:00>2021-02-14</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar-check"></i> </span><span class=post-meta-item-text>更新于</span> <time title="修改时间：2021-02-28 20:02:18" datetime=2021-02-28T20:02:18+08:00 itemprop=dateModified>2021-02-28</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/%E5%B9%B6%E5%8F%91/ itemprop=url rel=index><span itemprop=name>并发</span></a> </span></span><span class="post-meta-item leancloud_visitors" data-flag-title=AQS篇一 id=/2021/02/14/AQS%E7%AF%87%E4%B8%80/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-comment"></i> </span><span class=post-meta-item-text>Disqus：</span> <a href=/2021/02/14/AQS%E7%AF%87%E4%B8%80/#disqus_thread itemprop=discussionUrl title=disqus><span class="post-comments-count disqus-comment-count" data-disqus-identifier=2021/02/14/AQS篇一/ itemprop=commentCount></span></a></span></div></div></header><div class=post-body itemprop=articleBody><p>很多东西都是时看时新，而且时间长了也会忘，所以再来复习下，也会有一些新的角度看法这次来聊下AQS的内容，主要是这几个点，<h2 id=第一个线程><a class=headerlink href=#第一个线程 title=第一个线程></a>第一个线程</h2><p>第一个线程抢到锁了，此时state跟阻塞队列是怎么样的，其实这里是之前没理解对的地方<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
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|
* Fair version of tryAcquire. Don't grant access unless
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|
* recursive call or no waiters or is first.
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|
*/</span>
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|
<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">tryAcquire</span><span class="token punctuation">(</span><span class="token keyword">int</span> acquires<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">final</span> <span class="token class-name">Thread</span> current <span class="token operator">=</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">int</span> c <span class="token operator">=</span> <span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 这里如果state还是0说明锁还空着</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>c <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment">// 因为是公平锁版本的，先去看下是否阻塞队列里有排着队的</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">hasQueuedPredecessors</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span>
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<span class="token function">compareAndSetState</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> acquires<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment">// 没有排队的，并且state使用cas设置成功的就标记当前占有锁的线程是我</span>
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<span class="token function">setExclusiveOwnerThread</span><span class="token punctuation">(</span>current<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 然后其实就返回了，包括阻塞队列的head和tail节点和waitStatus都没有设置</span>
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<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>current <span class="token operator">==</span> <span class="token function">getExclusiveOwnerThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">int</span> nextc <span class="token operator">=</span> c <span class="token operator">+</span> acquires<span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>nextc <span class="token operator"><</span> <span class="token number">0</span><span class="token punctuation">)</span>
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<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Error</span><span class="token punctuation">(</span><span class="token string">"Maximum lock count exceeded"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token function">setState</span><span class="token punctuation">(</span>nextc<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
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|
<span class="token punctuation">}</span>
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<span class="token comment">// 这里就是第二个线程会返回false</span>
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<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><h2 id=第二个线程><a class=headerlink href=#第二个线程 title=第二个线程></a>第二个线程</h2><p>当第二个线程进来的时候应该是怎么样，结合代码来看<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
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|
* Acquires in exclusive mode, ignoring interrupts. Implemented
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|
* by invoking at least once {@link #tryAcquire},
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|
* returning on success. Otherwise the thread is queued, possibly
|
|
* repeatedly blocking and unblocking, invoking {@link
|
|
* #tryAcquire} until success. This method can be used
|
|
* to implement method {@link Lock#lock}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
*/</span>
|
|
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">void</span> <span class="token function">acquire</span><span class="token punctuation">(</span><span class="token keyword">int</span> arg<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
<span class="token comment">// 前面第一种情况是tryAcquire直接成功了，这个if判断第一个条件就是false，就不往下执行了</span>
|
|
<span class="token comment">// 如果是第二个线程，第一个条件获取锁不成功，条件判断!tryAcquire(arg) == true，就会走</span>
|
|
<span class="token comment">// acquireQueued(addWaiter(Node.EXCLUSIVE), arg)</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">tryAcquire</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span> <span class="token operator">&&</span>
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|
<span class="token function">acquireQueued</span><span class="token punctuation">(</span><span class="token function">addWaiter</span><span class="token punctuation">(</span><span class="token class-name">Node</span><span class="token punctuation">.</span><span class="token constant">EXCLUSIVE</span><span class="token punctuation">)</span><span class="token punctuation">,</span> arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
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|
<span class="token function">selfInterrupt</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>然后来看下addWaiter的逻辑<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Creates and enqueues node for current thread and given mode.
|
|
*
|
|
* @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared
|
|
* @return the new node
|
|
*/</span>
|
|
<span class="token keyword">private</span> <span class="token class-name">Node</span> <span class="token function">addWaiter</span><span class="token punctuation">(</span><span class="token class-name">Node</span> mode<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
<span class="token comment">// 这里是包装成一个node</span>
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|
<span class="token class-name">Node</span> node <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Node</span><span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> mode<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// Try the fast path of enq; backup to full enq on failure</span>
|
|
<span class="token comment">// 最快的方式就是把当前线程的节点放在阻塞队列的最后</span>
|
|
<span class="token class-name">Node</span> pred <span class="token operator">=</span> tail<span class="token punctuation">;</span>
|
|
<span class="token comment">// 只有当tail，也就是pred不为空的时候可以直接接上</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span>pred <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
node<span class="token punctuation">.</span>prev <span class="token operator">=</span> pred<span class="token punctuation">;</span>
|
|
<span class="token comment">// 如果这里cas成功了，就直接接上返回了</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">compareAndSetTail</span><span class="token punctuation">(</span>pred<span class="token punctuation">,</span> node<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
pred<span class="token punctuation">.</span>next <span class="token operator">=</span> node<span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> node<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token comment">// 不然就会继续走到这里</span>
|
|
<span class="token function">enq</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> node<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>然后就是enq的逻辑了<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Inserts node into queue, initializing if necessary. See picture above.
|
|
* @param node the node to insert
|
|
* @return node's predecessor
|
|
*/</span>
|
|
<span class="token keyword">private</span> <span class="token class-name">Node</span> <span class="token function">enq</span><span class="token punctuation">(</span><span class="token keyword">final</span> <span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token punctuation">;</span><span class="token punctuation">;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 如果状态没变化的话，tail这时还是null的</span>
|
|
<span class="token class-name">Node</span> t <span class="token operator">=</span> tail<span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>t <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// Must initialize</span>
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|
<span class="token comment">// 这里就会初始化头结点，就是个空节点</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">compareAndSetHead</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Node</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
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|
<span class="token comment">// tail也赋值成head</span>
|
|
tail <span class="token operator">=</span> head<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 这里就设置tail了</span>
|
|
node<span class="token punctuation">.</span>prev <span class="token operator">=</span> t<span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">compareAndSetTail</span><span class="token punctuation">(</span>t<span class="token punctuation">,</span> node<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
t<span class="token punctuation">.</span>next <span class="token operator">=</span> node<span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> t<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>所以从这里可以看出来，其实head头结点不是个真实的带有线程的节点，并且不是在第一个线程进来的时候设置的<h2 id=解锁><a class=headerlink href=#解锁 title=解锁></a>解锁</h2><p>通过代码来看下<pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token comment">/**
|
|
* Attempts to release this lock.
|
|
*
|
|
* <p>If the current thread is the holder of this lock then the hold
|
|
* count is decremented. If the hold count is now zero then the lock
|
|
* is released. If the current thread is not the holder of this
|
|
* lock then {@link IllegalMonitorStateException} is thrown.
|
|
*
|
|
* @throws IllegalMonitorStateException if the current thread does not
|
|
* hold this lock
|
|
*/</span>
|
|
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">unlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 释放锁</span>
|
|
sync<span class="token punctuation">.</span><span class="token function">release</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token comment">/**
|
|
* Releases in exclusive mode. Implemented by unblocking one or
|
|
* more threads if {@link #tryRelease} returns true.
|
|
* This method can be used to implement method {@link Lock#unlock}.
|
|
*
|
|
* @param arg the release argument. This value is conveyed to
|
|
* {@link #tryRelease} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @return the value returned from {@link #tryRelease}
|
|
*/</span>
|
|
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">release</span><span class="token punctuation">(</span><span class="token keyword">int</span> arg<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 尝试去释放</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">tryRelease</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token class-name">Node</span> h <span class="token operator">=</span> head<span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>h <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">&&</span> h<span class="token punctuation">.</span>waitStatus <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span>
|
|
<span class="token function">unparkSuccessor</span><span class="token punctuation">(</span>h<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">tryRelease</span><span class="token punctuation">(</span><span class="token keyword">int</span> releases<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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|
<span class="token keyword">int</span> c <span class="token operator">=</span> <span class="token function">getState</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> releases<span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token function">getExclusiveOwnerThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalMonitorStateException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">boolean</span> free <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
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|
<span class="token comment">// 判断是否完全释放锁，因为可重入</span>
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|
<span class="token keyword">if</span> <span class="token punctuation">(</span>c <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
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free <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
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<span class="token function">setExclusiveOwnerThread</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
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<span class="token punctuation">}</span>
|
|
<span class="token function">setState</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> free<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
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<span class="token comment">// 这段代码和上面的一致，只是为了顺序性，又拷下来看下</span>
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|
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|
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">release</span><span class="token punctuation">(</span><span class="token keyword">int</span> arg<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 尝试去释放，如果是完全释放，返回的就是true，否则是false</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">tryRelease</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token class-name">Node</span> h <span class="token operator">=</span> head<span class="token punctuation">;</span>
|
|
<span class="token comment">// 这里判断头结点是否为空以及waitStatus的状态，前面说了head节点其实是</span>
|
|
<span class="token comment">// 在第二个线程进来的时候初始化的，如果是空的话说明没后续节点，并且waitStatus</span>
|
|
<span class="token comment">// 也表示了后续的等待状态</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>h <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">&&</span> h<span class="token punctuation">.</span>waitStatus <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span>
|
|
<span class="token function">unparkSuccessor</span><span class="token punctuation">(</span>h<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
|
|
<span class="token comment">/**
|
|
* Wakes up node's successor, if one exists.
|
|
*
|
|
* @param node the node
|
|
*/</span>
|
|
<span class="token comment">// 唤醒后继节点</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">unparkSuccessor</span><span class="token punctuation">(</span><span class="token class-name">Node</span> node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">/*
|
|
* If status is negative (i.e., possibly needing signal) try
|
|
* to clear in anticipation of signalling. It is OK if this
|
|
* fails or if status is changed by waiting thread.
|
|
*/</span>
|
|
<span class="token keyword">int</span> ws <span class="token operator">=</span> node<span class="token punctuation">.</span>waitStatus<span class="token punctuation">;</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>ws <span class="token operator"><</span> <span class="token number">0</span><span class="token punctuation">)</span>
|
|
<span class="token function">compareAndSetWaitStatus</span><span class="token punctuation">(</span>node<span class="token punctuation">,</span> ws<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">/*
|
|
* Thread to unpark is held in successor, which is normally
|
|
* just the next node. But if cancelled or apparently null,
|
|
* traverse backwards from tail to find the actual
|
|
* non-cancelled successor.
|
|
*/</span>
|
|
<span class="token class-name">Node</span> s <span class="token operator">=</span> node<span class="token punctuation">.</span>next<span class="token punctuation">;</span>
|
|
<span class="token comment">// 如果后继节点是空或者当前节点取消等待了</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>s <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">||</span> s<span class="token punctuation">.</span>waitStatus <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
s <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 从后往前找，找到非取消的节点，注意这里不是找到就退出，而是一直找到头</span>
|
|
<span class="token comment">// 所以不必担心中间有取消的</span>
|
|
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">Node</span> t <span class="token operator">=</span> tail<span class="token punctuation">;</span> t <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">&&</span> t <span class="token operator">!=</span> node<span class="token punctuation">;</span> t <span class="token operator">=</span> t<span class="token punctuation">.</span>prev<span class="token punctuation">)</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>t<span class="token punctuation">.</span>waitStatus <span class="token operator"><=</span> <span class="token number">0</span><span class="token punctuation">)</span>
|
|
s <span class="token operator">=</span> t<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
<span class="token keyword">if</span> <span class="token punctuation">(</span>s <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
|
|
<span class="token comment">// 将其唤醒</span>
|
|
<span class="token class-name">LockSupport</span><span class="token punctuation">.</span><span class="token function">unpark</span><span class="token punctuation">(</span>s<span class="token punctuation">.</span>thread<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre></div><footer class=post-footer><div class=post-eof></div></footer></article></div><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article><link href=https://nicksxs.me/2021/02/07/%E5%85%B3%E4%BA%8E%E8%AF%BB%E4%B9%A6%E6%89%93%E5%8D%A1%E4%B8%8E%E5%88%86%E4%BA%AB/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="undefined | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h2 itemprop="name headline" class=post-title><a class=post-title-link href=/2021/02/07/%E5%85%B3%E4%BA%8E%E8%AF%BB%E4%B9%A6%E6%89%93%E5%8D%A1%E4%B8%8E%E5%88%86%E4%BA%AB/ itemprop=url>关于读书打卡与分享</a></h2><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2021-02-07 23:13:39" datetime=2021-02-07T23:13:39+08:00>2021-02-07</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E7%94%9F%E6%B4%BB/ itemprop=url rel=index><span itemprop=name>生活</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E8%AF%BB%E5%90%8E%E6%84%9F/ itemprop=url rel=index><span itemprop=name>读后感</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E8%AF%BB%E5%90%8E%E6%84%9F/%E7%99%BD%E5%B2%A9%E6%9D%BE/ itemprop=url rel=index><span itemprop=name>白岩松</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E8%AF%BB%E5%90%8E%E6%84%9F/%E7%99%BD%E5%B2%A9%E6%9D%BE/%E5%B9%B8%E7%A6%8F%E4%BA%86%E5%90%97/ itemprop=url rel=index><span itemprop=name>幸福了吗</span></a> </span></span><span class="post-meta-item leancloud_visitors" data-flag-title=关于读书打卡与分享 id=/2021/02/07/%E5%85%B3%E4%BA%8E%E8%AF%BB%E4%B9%A6%E6%89%93%E5%8D%A1%E4%B8%8E%E5%88%86%E4%BA%AB/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-comment"></i> </span><span class=post-meta-item-text>Disqus：</span> <a href=/2021/02/07/%E5%85%B3%E4%BA%8E%E8%AF%BB%E4%B9%A6%E6%89%93%E5%8D%A1%E4%B8%8E%E5%88%86%E4%BA%AB/#disqus_thread itemprop=discussionUrl title=disqus><span class="post-comments-count disqus-comment-count" data-disqus-identifier=2021/02/07/关于读书打卡与分享/ itemprop=commentCount></span></a></span></div></div></header><div class=post-body itemprop=articleBody><p>最近群里大佬发起了一个读书打卡活动，需要每天读一会书，在群里打卡分享感悟，争取一个月能读完一本书，说实话一天十分钟的读书时间倒是问题不大，不过每天都要打卡，而且一个月要读完一本书，其实难度还是有点大的，不过也想试试看。<br>之前某某老大给自己立了个 flag，说要读一百本书，这对我来说挺难实现的，一则我也不喜欢书只读一小半，二则感觉对于喜欢看的内容范围还是比较有限制，可能也算是比较矫情，不爱追热门的各类东西，因为往往会有一些跟大众不一致的观点看法，显得格格不入。所以还是这个打卡活动可能会比较适合我，书是人类进步的阶梯。<br>到现在是打卡了三天了，读的主要是白岩松的《幸福了吗》，对于白岩松，我们这一代人是比较熟悉，并且整体印象比较不错的一个央视主持人，从《焦点访谈》开始，到疫情期间的各类一线节目，可能对我来说是个三观比较正，敢于说一些真话的主持人，这中间其实是有个空档期，没怎么看电视，也不太关注了，只是在疫情期间的节目，还是一如既往地给人一种可靠的感觉，正好有一次偶然微信读书推荐了白岩松的这本书，就看了一部分，正好这次继续往下看，因为相对来讲不会很晦涩，并且从这位知名央视主持人的角度分享他的过往和想法看法，还是比较有意思的。<br>从对汶川地震，08 年奥运等往事的回忆和一些细节的呈现，也让我了解比较多当时所不知道的，特别是汶川地震，那时的我还在读高中，真的是看着电视，作为“猛男”都忍不住泪目了，共和国之殇，多难兴邦，但是这对于当事人来说，都是一场醒不过来的噩梦。<br>然后是对于足球的热爱，其实光这个就能掰扯很多，因为我不爱足球，只爱篮球，其中原因有的没的也挺多可以说的，但是看了他的书，才能比较深入的了解一个足球迷，对足球，对中国足球，对世界杯，对阿根廷的感情。<br>接下去还是想能继续坚持下去，加油！</div><footer class=post-footer><div class=post-eof></div></footer></article></div><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article><link href=https://nicksxs.me/2021/01/31/%E8%81%8A%E8%81%8A-redis-%E7%BC%93%E5%AD%98%E7%9A%84%E5%BA%94%E7%94%A8%E9%97%AE%E9%A2%98/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="undefined | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h2 itemprop="name headline" class=post-title><a class=post-title-link href=/2021/01/31/%E8%81%8A%E8%81%8A-redis-%E7%BC%93%E5%AD%98%E7%9A%84%E5%BA%94%E7%94%A8%E9%97%AE%E9%A2%98/ itemprop=url>聊聊 redis 缓存的应用问题</a></h2><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2021-01-31 23:02:44" datetime=2021-01-31T23:02:44+08:00>2021-01-31</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/ itemprop=url rel=index><span itemprop=name>Redis</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/%E5%BA%94%E7%94%A8/ itemprop=url rel=index><span itemprop=name>应用</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/%E7%BC%93%E5%AD%98/ itemprop=url rel=index><span itemprop=name>缓存</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E7%BC%93%E5%AD%98/ itemprop=url rel=index><span itemprop=name>缓存</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E7%BC%93%E5%AD%98/%E7%A9%BF%E9%80%8F/ itemprop=url rel=index><span itemprop=name>穿透</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E7%BC%93%E5%AD%98/%E7%A9%BF%E9%80%8F/%E5%87%BB%E7%A9%BF/ itemprop=url rel=index><span itemprop=name>击穿</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/%E7%BC%93%E5%AD%98/%E7%A9%BF%E9%80%8F/%E5%87%BB%E7%A9%BF/%E9%9B%AA%E5%B4%A9/ itemprop=url rel=index><span itemprop=name>雪崩</span></a> </span></span><span class="post-meta-item leancloud_visitors" data-flag-title="聊聊 redis 缓存的应用问题" id=/2021/01/31/%E8%81%8A%E8%81%8A-redis-%E7%BC%93%E5%AD%98%E7%9A%84%E5%BA%94%E7%94%A8%E9%97%AE%E9%A2%98/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-comment"></i> </span><span class=post-meta-item-text>Disqus：</span> <a href=/2021/01/31/%E8%81%8A%E8%81%8A-redis-%E7%BC%93%E5%AD%98%E7%9A%84%E5%BA%94%E7%94%A8%E9%97%AE%E9%A2%98/#disqus_thread itemprop=discussionUrl title=disqus><span class="post-comments-count disqus-comment-count" data-disqus-identifier=2021/01/31/聊聊-redis-缓存的应用问题/ itemprop=commentCount></span></a></span></div></div></header><div class=post-body itemprop=articleBody><p>前面写过一系列的 redis 源码分析的，但是实际上很多的问题还是需要结合实际的使用，然后其实就避不开缓存使用的三个著名问题，穿透，击穿和雪崩，这三个概念也是有着千丝万缕的关系，<h3 id=缓存穿透><a class=headerlink href=#缓存穿透 title=缓存穿透></a>缓存穿透</h3><p>缓存穿透是指当数据库中本身就不存在这个数据的时候，使用一般的缓存策略时访问不到缓存后就访问数据库，但是因为数据库也没数据，所以如果不做任何策略优化的话，这类数据就每次都会访问一次数据库，对数据库压力也会比较大。<h3 id=缓存击穿><a class=headerlink href=#缓存击穿 title=缓存击穿></a>缓存击穿</h3><p>缓存击穿跟穿透比较类似的，都是访问缓存不在，然后去访问数据库，与穿透不一样的是击穿是在数据库中存在数据，但是可能由于第一次访问，或者缓存过期了，需要访问到数据库，这对于访问量小的情况其实算是个正常情况，但是随着请求量变高就会引发一些性能隐患。<h3 id=缓存雪崩><a class=headerlink href=#缓存雪崩 title=缓存雪崩></a>缓存雪崩</h3><p>缓存雪崩就是击穿的大规模集群效应，当大量的缓存过期失效的时候，这些请求都是直接访问到数据库了，会对数据库造成很大的压力。<p>对于以上三种场景也有一些比较常见的解决方案，但也不能说是万无一失的，需要随着业务去寻找合适的方案<h3 id=解决缓存穿透><a class=headerlink href=#解决缓存穿透 title=解决缓存穿透></a>解决缓存穿透</h3><p>对于数据库中就没这个数据的时候，一种是可以对这个 key 设置下空值，即以一个特定的表示是数据库不存在的，这种情况需要合理地调整过期时间，当这个 key 在数据库中有数据了的话，也需要有策略去更新这个值，并且如果这类 key 非常多，这个方法就会不太合适，就可以使用第二种方法，就是布隆过滤器，bloom filter，前置一个布隆过滤器，当这个 key 在数据库不存在的话，先用布隆过滤器挡一道，如果不在的话就直接返回了，当然布隆过滤器不是绝对的准确的<h3 id=解决缓存击穿><a class=headerlink href=#解决缓存击穿 title=解决缓存击穿></a>解决缓存击穿</h3><p>当一个 key 的缓存过期了，如果大量请求过来访问这个 key，请求都会落在数据库里，这个时候就可以使用一些类似于互斥锁的方式去让一个线程去访问数据库，更新缓存，但是这里其实也有个问题，就是如果是热点 key 其实这种方式也比较危险，万一更新失败，或者更新操作的时候耗时比较久，就会有一大堆请求卡在那，这种情况可能需要有一些异步提前刷新缓存，可以结合具体场景选择方式<h3 id=解决缓存雪崩><a class=headerlink href=#解决缓存雪崩 title=解决缓存雪崩></a>解决缓存雪崩</h3><p>雪崩的情况是指大批量的 key 都一起过期了，击穿的放大版，大批量的请求都打到数据库上了，一方面有可能直接缓存不可用了，就需要用集群化高可用的缓存服务，然后对于实际使用中也可以使用本地缓存结合 redis 缓存，去提高可用性，再配合一些限流措施，然后就是缓存使用过程总的过期时间最好能加一些随机值，防止在同一时间过期而导致雪崩，结合互斥锁防止大量请求打到数据库。</div><footer class=post-footer><div class=post-eof></div></footer></article></div><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article><link href=https://nicksxs.me/2021/01/24/Leetcode-124-%E4%BA%8C%E5%8F%89%E6%A0%91%E4%B8%AD%E7%9A%84%E6%9C%80%E5%A4%A7%E8%B7%AF%E5%BE%84%E5%92%8C-Binary-Tree-Maximum-Path-Sum-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="learn from zero,技术博客，Nicksxs，史学森" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="undefined | Nicksxs's Blog" itemprop=name><meta itemprop=description></span><header class=post-header><h2 itemprop="name headline" class=post-title><a class=post-title-link href=/2021/01/24/Leetcode-124-%E4%BA%8C%E5%8F%89%E6%A0%91%E4%B8%AD%E7%9A%84%E6%9C%80%E5%A4%A7%E8%B7%AF%E5%BE%84%E5%92%8C-Binary-Tree-Maximum-Path-Sum-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/ itemprop=url>Leetcode 124 二叉树中的最大路径和(Binary Tree Maximum Path Sum) 题解分析</a></h2><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间：2021-01-24 22:45:03" datetime=2021-01-24T22:45:03+08:00>2021-01-24</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar-check"></i> </span><span class=post-meta-item-text>更新于</span> <time title="修改时间：2022-06-11 22:45:11" datetime=2022-06-11T22:45:11+08:00 itemprop=dateModified>2022-06-11</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/leetcode/ itemprop=url rel=index><span itemprop=name>leetcode</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Binary-Tree/ itemprop=url rel=index><span itemprop=name>Binary Tree</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/leetcode/java/ itemprop=url rel=index><span itemprop=name>java</span></a> </span>， <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/leetcode/java/Binary-Tree/ itemprop=url rel=index><span itemprop=name>Binary Tree</span></a> </span></span><span class="post-meta-item leancloud_visitors" data-flag-title="Leetcode 124 二叉树中的最大路径和(Binary Tree Maximum Path Sum) 题解分析" id=/2021/01/24/Leetcode-124-%E4%BA%8C%E5%8F%89%E6%A0%91%E4%B8%AD%E7%9A%84%E6%9C%80%E5%A4%A7%E8%B7%AF%E5%BE%84%E5%92%8C-Binary-Tree-Maximum-Path-Sum-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数：</span> <span class=leancloud-visitors-count></span> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-comment"></i> </span><span class=post-meta-item-text>Disqus：</span> <a href=/2021/01/24/Leetcode-124-%E4%BA%8C%E5%8F%89%E6%A0%91%E4%B8%AD%E7%9A%84%E6%9C%80%E5%A4%A7%E8%B7%AF%E5%BE%84%E5%92%8C-Binary-Tree-Maximum-Path-Sum-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/#disqus_thread itemprop=discussionUrl title=disqus><span class="post-comments-count disqus-comment-count" data-disqus-identifier=2021/01/24/Leetcode-124-二叉树中的最大路径和-Binary-Tree-Maximum-Path-Sum-题解分析/ itemprop=commentCount></span></a></span></div></div></header><div class=post-body itemprop=articleBody><h3 id=题目介绍><a class=headerlink href=#题目介绍 title=题目介绍></a>题目介绍</h3><p>A <strong>path</strong> in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence <strong>at most once</strong>. Note that the path does not need to pass through the root.<p>The <strong>path sum</strong> of a path is the sum of the node’s values in the path.<p>Given the <code>root</code> of a binary tree, return the maximum <strong>path sum</strong> of any path.<p><strong>路径</strong> 被定义为一条从树中任意节点出发，沿父节点-子节点连接，达到任意节点的序列。该路径 <strong>至少包含一个</strong> 节点，且不一定经过根节点。<p><strong>路径和</strong> 是路径中各节点值的总和。<p>给你一个二叉树的根节点 <code>root</code> ，返回其 <strong>最大路径和</strong><h3 id=简要分析><a class=headerlink href=#简要分析 title=简要分析></a>简要分析</h3><p>其实这个题目会被误解成比较简单，左子树最大的，或者右子树最大的，或者两边加一下，仔细想想都不对，其实有可能是产生于左子树中，或者右子树中，这两个都是指跟左子树根还有右子树根没关系的，这么说感觉不太容易理解，画个图<br><img data-src=https://img.nicksxs.com/uPic/SfxIEy.png><br>可以看到图里，其实最长路径和是左边这个子树组成的，跟根节点还有右子树完全没关系，然后再想一种情况，如果是整棵树就是图中的左子树，那么这个最长路径和就是左子树加右子树加根节点了，所以不是我一开始想得那么简单，在代码实现中也需要一些技巧<h3 id=代码><a class=headerlink href=#代码 title=代码></a>代码</h3><pre class="line-numbers language-java" data-language=java><code class=language-java><span class="token keyword">int</span> ansNew <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token constant">MIN_VALUE</span><span class="token punctuation">;</span>
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<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">maxPathSum</span><span class="token punctuation">(</span><span class="token class-name">TreeNode</span> root<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token function">maxSumNew</span><span class="token punctuation">(</span>root<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> ansNew<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">maxSumNew</span><span class="token punctuation">(</span><span class="token class-name">TreeNode</span> root<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>root <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 这里是个简单的递归，就是去递归左右子树，但是这里其实有个概念，当这样处理时，其实相当于把子树的内部的最大路径和已经算出来了</span>
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<span class="token keyword">int</span> left <span class="token operator">=</span> <span class="token function">maxSumNew</span><span class="token punctuation">(</span>root<span class="token punctuation">.</span>left<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">int</span> right <span class="token operator">=</span> <span class="token function">maxSumNew</span><span class="token punctuation">(</span>root<span class="token punctuation">.</span>right<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 这里前面我有点没想明白，但是看到 ansNew 的比较，其实相当于，返回的是三种情况里的最大值，一个是左子树+根，一个是右子树+根，一个是单独根节点，</span>
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<span class="token comment">// 这样这个递归的返回才会有意义，不然像原来的方法，它可能是跳着的，但是这种情况其实是借助于 ansNew 这个全局的最大值，因为原来我觉得要比较的是</span>
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<span class="token comment">// left, right, left + root , right + root, root, left + right + root 这些的最大值，这里是分成了两个阶段，left 跟 right 的最大值已经在上面的</span>
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<span class="token comment">// 调用过程中赋值给 ansNew 了 </span>
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<span class="token keyword">int</span> currentSum <span class="token operator">=</span> <span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>root<span class="token punctuation">.</span>val <span class="token operator">+</span> left <span class="token punctuation">,</span> root<span class="token punctuation">.</span>val <span class="token operator">+</span> right<span class="token punctuation">)</span><span class="token punctuation">,</span> root<span class="token punctuation">.</span>val<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 这边返回的是 currentSum，然后再用它跟 left + right + root 进行对比，然后再去更新 ans</span>
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<span class="token comment">// PS: 有个小点也是这边的破局点，就是这个 ansNew</span>
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<span class="token keyword">int</span> res <span class="token operator">=</span> <span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>left <span class="token operator">+</span> right <span class="token operator">+</span> root<span class="token punctuation">.</span>val<span class="token punctuation">,</span> currentSum<span class="token punctuation">)</span><span class="token punctuation">;</span>
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ans <span class="token operator">=</span> <span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>res<span class="token punctuation">,</span> ans<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> currentSum<span class="token punctuation">;</span>
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<span class="token punctuation">}</span><span aria-hidden=true class=line-numbers-rows><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>这里非常重要的就是 ansNew 是最后的一个结果，而对于 maxSumNew 这个函数的返回值其实是需要包含了一个连续结果，因为要返回继续去算路径和，所以返回的是 currentSum，最终结果是 ansNew<h3 id=结果图><a class=headerlink href=#结果图 title=结果图></a>结果图</h3><p>难得有个 100%，贴个图哈哈<br><img data-src=https://img.nicksxs.com/uPic/iipgv0.png></div><footer class=post-footer><div class=post-eof></div></footer></article></div><nav class=pagination><a class="extend prev" aria-label=上一页 href=/page/27/ rel=prev title=上一页><i class="fa fa-angle-left"></i></a><a class=page-number href=/>1</a><span class=space>…</span><a class=page-number href=/page/27/>27</a><span 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