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<a href="/2020/06/21/%E4%BB%8B%E7%BB%8D%E4%B8%80%E4%B8%8B-RocketMQ/" class="post-title-link" itemprop="url">介绍一下 RocketMQ</a>
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<p>说起消息队列一般Web后端做过一段时间开发的肯定会用过，在前司的时候用的是改良版的 NSQ，有点像 NOSQL 的简写版🙄，其实是个go 语言写的消息队列，<a href="https://github.com/nsqio/nsq" target="_blank" rel="noopener">nsq</a> 看代码提交感觉最近更新的不是很勤，不过因为前司有专门的中间件团队，所以还是挺好用的，而且中间件团队的大牛也很厉害，一次都没碰到过丢消息之类的错误，然后现在公司用的是 RocketMQ，本着总还是要了解下的，并且消息队列也是服务端开发中一个很重要的中间件，因为不太有不需要用消息队列的后端团队了吧，原来对 nsq 也不是特别了解原理，就打算了解下 RocketMQ。</p>
<p>还是像我这样的小白专属，消息队列用来干啥，很多都是标准答案，用来削峰填谷的，这个完全对，只是我想结合场景说给像我这样的小白同学听，想想一个电商的下单功能，除了 AT 两家之外应该大部分都是接入的支付，那么下单支付完成后一般都是等支付回调，告诉你支付完成了（也有可能是失败了，或者超时了咱们主动去查），然后这个回调里我们自己的业务代码干点啥，首先比如是把订单状态改掉了，然后会有各类的操作，比如把优惠券核销了，把其他金钱相关的也核销了，把购物车里对应的商品给删了，还有更次要的，比如发个客服消息，让用户确认下地址的，给用户加积分的等等等等，想象下如果这些都是回调里一股脑儿做掉了，那可能你的代码健壮性跟相关服务的稳定性还有性能要达到一个非常高的水平才能让业务不出现异常，并且万一流量打起来了，这些重要的不重要的操作都会阻塞着，所以需要用一个消息队列，在接到回调后只处理极少的几个核心操作，完了就把这个消息丢进消息队列里，让各个业务方去消费这个消息，把客服消息发一下，给用户加个积分等等，这样子主要的业务流程需要处理的事情就少了，速度也加快了，这个例子呢不能严格算是削峰填谷的例子，不过也算是消息队列的比较典型的使用场景了，要说真实的削峰填谷的话其实可以这么理解，假如短时间内有 1w 个请求进来，系统能支持的 QPS 才 1000，那么正常情况下服务就挂了，或者被限流了，为了让服务正常，那么可以把这些请求先放进消息队列里，我服务端以拉的模式按我的处理能力来消费，这样就没啥问题了</p>
<p>扯了这么多来聊聊 RocketMQ 长啥样</p>
<p><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/6073827-a998e005dd13967c.png" alt="6073827-a998e005dd13967c"></p>
<p>总共有四大部分：<strong>NameServer，Broker，Producer，Consumer。</strong></p>
<h4 id="NameServer"><a href="#NameServer" class="headerlink" title="NameServer"></a>NameServer</h4><p>NameServer是一个非常简单的Topic路由注册中心，其角色类似Dubbo中的zookeeper，支持Broker的动态注册与发现。主要包括两个功能：Broker管理，NameServer接受Broker集群的注册信息并且保存下来作为路由信息的基本数据。然后提供心跳检测机制，检查Broker是否还存活；路由信息管理，每个NameServer将保存关于Broker集群的整个路由信息和用于客户端查询的队列信息。然后Producer和Conumser通过NameServer就可以知道整个Broker集群的路由信息，从而进行消息的投递和消费。NameServer通常也是集群的方式部署，各实例间相互不进行信息通讯。Broker是向每一台NameServer注册自己的路由信息，所以每一个NameServer实例上面都保存一份完整的路由信息。当某个NameServer因某种原因下线了，Broker仍然可以向其它NameServer同步其路由信息，Producer,Consumer仍然可以动态感知Broker的路由的信息。</p>
<p>NameServer压力不会太大，正常情况主要负责维持心跳和提供Topic-Broker的关系数据。但有一点需要注意，Broker向Namesr发心跳时，会带上当前自己所负责的所有Topic信息，<strong>如果Topic个数太多，会导致一次心跳中，光Topic的数据就非常大，网络情况差的话，网络传输失败，心跳失败，导致Namesrv误认为Broker心跳失败。</strong></p>
<h4 id="Broker"><a href="#Broker" class="headerlink" title="Broker"></a>Broker</h4><p>Broker主要负责消息的存储、投递和查询以及服务高可用保证，为了实现这些功能，Broker包含了以下几个重要子模块。</p>
<ul>
<li>Remoting Module：整个Broker的实体，负责处理来自clients端的请求。</li>
<li>Client Manager：负责管理客户端(Producer/Consumer)和维护Consumer的Topic订阅信息</li>
<li>Store Service：提供方便简单的API接口处理消息存储到物理硬盘和查询功能。</li>
<li>HA Service：高可用服务，提供Master Broker 和 Slave Broker之间的数据同步功能。</li>
<li>Index Service：根据特定的Message key对投递到Broker的消息进行索引服务，以提供消息的快速查询。</li>
</ul>
<h6 id="Broker的特点"><a href="#Broker的特点" class="headerlink" title="Broker的特点"></a>Broker的特点</h6><p><strong>1.负载均衡：</strong>Broker上存Topic信息，<strong>Topic由多个队列组成，队列会平均分散在多个Broker上，</strong>而Producer的发送机制保证消息尽量平均分布到所有队列中，<strong>最终效果就是所有消息都平均落在每个Broker上。</strong></p>
<p><strong>2.动态伸缩能力（非顺序消息）</strong>：Broker的伸缩性体现在两个维度：Topic, Broker。</p>
<blockquote>
<p><strong>Topic维度：</strong>假如一个Topic的消息量特别大，但集群水位压力还是很低，就可以扩大该Topic的队列数，Topic的队列数跟发送、消费速度成正比。<br> <strong>Broker维度：</strong>如果集群水位很高了，需要扩容，直接加机器部署Broker就可以。Broker起来后想NameServer注册，Producer、Consumer通过NameServer发现新Broker，立即跟该Broker直连，收发消息。</p>
</blockquote>
<p><strong>3.高可用&amp;高可靠</strong></p>
<blockquote>
<p><strong>高可用：</strong>集群部署时一般都为主备，备机实时从主机同步消息，如果其中一个主机宕机，备机提供消费服务，但不提供写服务。<br> <strong>高可靠：</strong>所有发往broker的消息，有同步刷盘和异步刷盘机制；同步刷盘时，消息写入物理文件才会返回成功，异步刷盘时，只有机器宕机，才会产生消息丢失，broker挂掉可能会发生，但是机器宕机崩溃是很少发生的，除非突然断电</p>
</blockquote>
<h4 id="Producer"><a href="#Producer" class="headerlink" title="Producer"></a>Producer</h4><p>Producer与NameServer集群中的其中一个节点（随机选择）建立长连接，定期从NameServer获取Topic路由信息，并向提供Topic 服务的Master建立长连接，且定时向Master发送心跳。Producer完全无状态，可集群部署。<br> <strong>RocketMQ提供三种发送方式：</strong></p>
<blockquote>
<p><strong>同步：</strong>在广泛的场景中使用可靠的同步传输，如重要的通知信息、短信通知、短信营销系统等。<br> <strong>异步：</strong>异步发送通常用于响应时间敏感的业务场景，发送出去即刻返回，利用回调做后续处理。<br> <strong>一次性：</strong>一次性发送用于需要中等可靠性的情况，如日志收集，发送出去即完成，不用等待发送结果，回调等等。</p>
</blockquote>
<h6 id="生产者端的负载均衡"><a href="#生产者端的负载均衡" class="headerlink" title="生产者端的负载均衡"></a>生产者端的负载均衡</h6><p>生产者发送时，会自动轮询当前所有可发送的broker，一条消息发送成功，下次换另外一个broker发送，以达到消息平均落到所有的broker上。</p>
<h4 id="Consumer"><a href="#Consumer" class="headerlink" title="Consumer"></a>Consumer</h4><p>Consumer与NameServer集群中的其中一个节点（随机选择）建立长连接，定期从NameServer获取Topic路由信息，并向提供Topic服务的Master、Slave建立长连接，且定时向Master、Slave发送心跳。Consumer既可以从Master订阅消息，也可以从Slave订阅消息，消费者在向Master拉取消息时，Master服务器会根据拉取偏移量与最大偏移量的距离（判断是否读老消息，产生读I/O），以及从服务器是否可读等因素建议下一次是从Master还是Slave拉取。</p>
<h6 id="消费者端的负载均衡"><a href="#消费者端的负载均衡" class="headerlink" title="消费者端的负载均衡"></a>消费者端的负载均衡</h6><p>先讨论消费者的消费模式，<strong>消费者有两种模式消费：集群消费，广播消费。</strong></p>
<blockquote>
<p><strong>广播消费：每个消费者消费Topic下的所有队列。</strong><br> <strong>集群消费：一个topic可以由同一个ID下所有消费者分担消费。</strong><br> 具体例子：假如TopicA有6个队列，某个消费者ID起了2个消费者实例，那么每个消费者负责消费3个队列。如果再增加一个消费者ID相同消费者实例，即当前共有3个消费者同时消费6个队列，那每个消费者负责2个队列的消费。</p>
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<p>消费者端的负载均衡，就是集群消费模式下，同一个ID的所有消费者实例平均消费该Topic的所有队列。</p>
<p><strong>消费者从用户角度来看有两种类型：</strong></p>
<blockquote>
<p><strong>PullConsumer：主动从brokers处拉取消息。</strong>Consumer消费的一种类型，应用通常主动调用Consumer的拉消息方法从Broker服务器拉消息、主动权由应用控制。一旦获取了批量消息，应用就会启动消费过程。<br><strong>PushConsumer：Consumer消费的一种类型，该模式下Broker收到数据后会主动推送给消费端，该消费模式一般实时性较高。</strong></p>
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<h4 id="补充一些概念"><a href="#补充一些概念" class="headerlink" title="补充一些概念"></a>补充一些概念</h4><p><strong>Topic：主题，表示一类消息的集合，每个主题包含若干条消息，每条消息只能属于一个主题，是RocketMQ进行消息订阅的基本单位。</strong>Topic与生产者和消费者都是非常松散的关系，一个topic可以有0个或者1个或者多个生产者向其发送消息，换句话说，一个生产者可以同时向不同和topic发送消息。从消费者的解度来说，一个topic可能被0个或者一个或者多个消费组订阅，类似的，一个消费组可以订阅一个或者多个主题只要这个消费组的实例保持他们的订阅一致。</p>
<p><strong>Message：消息</strong>消息系统所传输信息的物理载体，生产和消费数据的最小单位，每条消息必须属于一个主题。RocketMQ中每个消息拥有唯一的Message ID，且可以携带具有业务标识的Key。系统提供了通过Message ID和Key查询消息的功能。。</p>
<p><strong>Message Queue：消息队列，</strong>一个主题被化分为一个或者多个子主题（sub-topics），“消息队列”.</p>
<p><strong>Tag：标签，为消息设置的标志，用于同一主题下区分不同类型的消息。来自同一业务单元的消息，可以根据不同业务目的在同一主题下设置不同标签。标签能够有效地保持代码的清晰度和连贯性，并优化RocketMQ提供的查询系统。消费者可以根据Tag实现对不同子主题的不同消费逻辑，实现更好的扩展性。</strong>使用tag，同一业务模块不同目的的messages就可以用相同topic不同tag来标识。Tags有益于保持你的代码干净而条理清晰，同时促进使用RocketMQ提供的查询系统的效率。Topic：主题，是生产者发送的消息和消费者拉取的消息的归类。Topic与生产者和消费者都是非常松散的关系，一个topic可以有0个或者1个或者多个生产者向其发送消息，换句话说，一个生产者可以同时向不同和topic发送消息。从消费者的解度来说，一个topic可能被0个或者一个或者多个消费组订阅，类似的，一个消费组可以订阅一个或者多个主题只要这个消费组的实例保持他们的订阅一致。</p>
<p><strong>Message Order：当使用DefaultMQPushConsumer时，你需要确定消费消息的方式：</strong></p>
<blockquote>
<p>Orderly：顺序地消费消息即表示消费的消息顺序同生产者发送的顺序一致。<br> Concurrently：并行消费。指定此方式消费，信息消费的最大并行数量仅受限于每个消费者客户端指定的线程池。</p>
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<p><strong>Consumer Group：消费组，</strong>同一类Consumer的集合，这类Consumer通常消费同一类消息且消费逻辑一致。消费者组使得在消息消费方面，实现负载均衡和容错的目标变得非常容易。要注意的是，消费者组的消费者实例必须订阅完全相同的Topic。RocketMQ 支持两种消息模式：集群消费（Clustering）和广播消费（Broadcasting）。<br><strong>Producer Group:生产者组，</strong>同一类Producer的集合，这类Producer发送同一类消息且发送逻辑一致。如果发送的是事务消息且原始生产者在发送之后崩溃，则Broker服务器会联系同一生产者组的其他生产者实例以提交或回溯消费。</p>
<p>上面的这些我主要参考了 RocketMQ 的 GitHub 介绍和一些优秀网文的介绍，侵权请联系我删除。</p>
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<p>熟悉我的人（谁熟悉你啊🙄）知道我以前写过 PHP，虽然现在在工作中没用到了，但是自己的一些小工具还是会用 PHP 来写，但是在 Mac 碰到了一个环境相关的问题，因为我也是个更新狂魔，用了 brew 之后因为 gfw 的原因，如果长时间不更新，有时候要装一个用它装一个软件的话，前置的更新耗时就会让人非常头大，所以我基本会隔天 update 一下，但是这样会带来一个很心烦的问题，就是像这样，因为我是要用一个固定版本的 PHP，如果一直升需要一直配扩展啥的也很麻烦，如果一直升级 PHP 到最新版可能会比较少碰到这个问题</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">dyld: Library not loaded: /usr/local/opt/icu4c/lib/libicui18n.64.dylib</span><br></pre></td></tr></table></figure>
<p>这是什么鬼啊，然后我去这个目录下看了下，已经都是libicui18n.67.dylib了，而且它没有把原来的版本保留下来，首先这个是个叫 icu4c是啥玩意，谷歌了一下</p>
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<p>ICU4C是ICU在C/C++平台下的版本, ICU(International Component for Unicode)是基于”IBM公共许可证”的，与开源组织合作研究的, 用于支持软件国际化的开源项目。ICU4C提供了C/C++平台强大的国际化开发能力，软件开发者几乎可以使用ICU4C解决任何国际化的问题，根据各地的风俗和语言习惯，实现对数字、货币、时间、日期、和消息的格式化、解析，对字符串进行大小写转换、整理、搜索和排序等功能，必须一提的是，ICU4C提供了强大的BIDI算法，对阿拉伯语等BIDI语言提供了完善的支持。</p>
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<p>然后首先想到的解决方案就是能不能我使用<code>brew install icu4c@64</code>来重装下原来的版本，发现不行，并木有，之前的做法就只能是去网上把 64 的下载下来，然后放到这个目录，比较麻烦不智能，虽然没抱着希望在谷歌着，不过这次竟然给我找到了一个我认为非常 nice 的解决方案，因为是在 Stack Overflow 找到的，本着写给像我这样的小小白看的，那就稍微翻译一下<br>第一步，我们到 brew的目录下</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">cd $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula</span><br></pre></td></tr></table></figure>
<p>这个可以理解为是 maven 的 pom 文件，不过有很多不同之处，使用ruby 写的，然后一个文件对应一个组件或者软件，那我们看下有个叫icu4c.rb的文件，<br>第二步看看它的提交历史</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">git log --follow icu4c.rb</span><br></pre></td></tr></table></figure>
<p>在 git log 的海洋中寻找，寻找它的(64版本)的身影<br><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/YzS7vN.png" alt=""><br>第三步注意这三个红框，Stack Overflow 给出来的答案这一步是找到这个 commit id 直接切出一个新分支</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">git checkout -b icu4c-63 e7f0f10dc63b1dc1061d475f1a61d01b70ef2cb7</span><br></pre></td></tr></table></figure>
<p>其实注意 commit id 旁边的红框，这个是有tag 的，可以直接</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">git checkout icu4c-64</span><br></pre></td></tr></table></figure>
<p>PS: 因为我的问题是出在 64 的问题，Stack Overflow 回答的是 63 的，反正是一样的解决方法<br>第四部，切回去之后我们就可以用 brew 提供的基于文件的安装命令来重新装上 64 版本</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">brew reinstall ./icu4c.rb</span><br></pre></td></tr></table></figure>
<p>然后就是第五步，切换版本</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">brew switch icu4c 64.2</span><br></pre></td></tr></table></figure>
<p>最后把分支切回来</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">git checkout master</span><br></pre></td></tr></table></figure>
<p>是不是感觉很厉害的解决方法，大佬还提供了一个更牛的，直接写个 zsh 方法</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#</span><span class="bash"> zsh</span></span><br><span class="line">function hiicu64() &#123;</span><br><span class="line"> local last_dir=$(pwd)</span><br><span class="line"></span><br><span class="line"> cd $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula</span><br><span class="line"> git checkout icu4c-4</span><br><span class="line"> brew reinstall ./icu4c.rb</span><br><span class="line"> brew switch icu4c 64.2</span><br><span class="line"> git checkout master</span><br><span class="line"></span><br><span class="line"> cd $last_dir</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>对应自己的版本改改版本号就可以了，非常好用。</p>
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<h2 id="Adaptive"><a href="#Adaptive" class="headerlink" title="Adaptive"></a>Adaptive</h2><p>这个应该是 Dubbo SPI 里最玄妙的东西了，一开始没懂，自适应扩展点加载，<br><code>dubbo://123.123.123.123:1234/com.nicksxs.demo.service.HelloWorldService?anyhost=true&amp;application=demo&amp;default.loadbalance=random&amp;default.service.filter=LoggerFilter&amp;dubbo=2.5.3&amp;interface=com.nicksxs.demo.service.HelloWorldService&amp;logger=slf4j&amp;methods=method1,method2,method3,method4&amp;pid=4292&amp;retries=0&amp;side=provider&amp;threadpool=fixed&amp;threads=200&amp;timeout=2000&amp;timestamp=1590647155886</code><br>那我从比较能理解的角度或者说思路去讲讲我的理解，因为直接将原理如果脱离了使用，对于我这样的理解能力比较差的可能会比较吃力，从使用场景开始讲可能会比较舒服了，这里可以看到参数里有蛮多的，举个例子，比如这个 <code>threadpool = fixed</code>，说明线程池使用的是 fixed 对应的实现，也就是下图的这个<br><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/4AAOaW.png" alt=""><br>这样子似乎没啥问题了，反正就是用dubbo 的 spi 加载嘛，好像没啥问题，其实问题还是存在的，或者说不太优雅，比如要先判断我这个 fixed 对应的实现类是哪个，这里可能就有个 if-else 判断了，但是 dubbo 的开发人员似乎不太想这么做这个事情，</p>
<p>譬如我们在引用一个服务时，在ReferenceConfig 中的</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol<span class="class">.<span class="keyword">class</span>).<span class="title">getAdaptiveExtension</span>()</span>;</span><br></pre></td></tr></table></figure>
<p>就获取了自适应拓展，</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> T <span class="title">getAdaptiveExtension</span><span class="params">()</span> </span>&#123;</span><br><span class="line"> Object instance = cachedAdaptiveInstance.get();</span><br><span class="line"> <span class="keyword">if</span> (instance == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">if</span> (createAdaptiveInstanceError == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">synchronized</span> (cachedAdaptiveInstance) &#123;</span><br><span class="line"> instance = cachedAdaptiveInstance.get();</span><br><span class="line"> <span class="keyword">if</span> (instance == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">try</span> &#123;</span><br><span class="line"> instance = createAdaptiveExtension();</span><br><span class="line"> cachedAdaptiveInstance.set(instance);</span><br><span class="line"> &#125; <span class="keyword">catch</span> (Throwable t) &#123;</span><br><span class="line"> createAdaptiveInstanceError = t;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(<span class="string">"fail to create adaptive instance: "</span> + t.toString(), t);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> &#125; <span class="keyword">else</span> &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(<span class="string">"fail to create adaptive instance: "</span> + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> (T) instance;</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
<p>这里也使用了 DCL，来锁cachedAdaptiveInstance，当缓存中没有时就去创建自适应拓展</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> T <span class="title">createAdaptiveExtension</span><span class="params">()</span> </span>&#123;</span><br><span class="line"> <span class="keyword">try</span> &#123;</span><br><span class="line"> <span class="comment">// 获取自适应拓展类然后实例化</span></span><br><span class="line"> <span class="keyword">return</span> injectExtension((T) getAdaptiveExtensionClass().newInstance());</span><br><span class="line"> &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(<span class="string">"Can not create adaptive extension "</span> + type + <span class="string">", cause: "</span> + e.getMessage(), e);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">private</span> Class&lt;?&gt; getAdaptiveExtensionClass() &#123;</span><br><span class="line"> <span class="comment">// 这里会获取拓展类，如果没有自适应的拓展类，那么就需要调用createAdaptiveExtensionClass</span></span><br><span class="line"> getExtensionClasses();</span><br><span class="line"> <span class="keyword">if</span> (cachedAdaptiveClass != <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">return</span> cachedAdaptiveClass;</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="keyword">return</span> cachedAdaptiveClass = createAdaptiveExtensionClass();</span><br><span class="line"> &#125;</span><br><span class="line"><span class="keyword">private</span> Class&lt;?&gt; createAdaptiveExtensionClass() &#123;</span><br><span class="line"> <span class="comment">// 这里去生成了自适应拓展的代码，具体生成逻辑比较复杂先不展开讲</span></span><br><span class="line"> String code = createAdaptiveExtensionClassCode();</span><br><span class="line"> ClassLoader classLoader = findClassLoader();</span><br><span class="line"> com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler<span class="class">.<span class="keyword">class</span>).<span class="title">getAdaptiveExtension</span>()</span>;</span><br><span class="line"> <span class="keyword">return</span> compiler.compile(code, classLoader);</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
<p>生成的代码像这样</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> com.alibaba.dubbo.rpc;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> com.alibaba.dubbo.common.extension.ExtensionLoader;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Protocol</span>$<span class="title">Adaptive</span> <span class="keyword">implements</span> <span class="title">com</span>.<span class="title">alibaba</span>.<span class="title">dubbo</span>.<span class="title">rpc</span>.<span class="title">Protocol</span> </span>&#123;</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">destroy</span><span class="params">()</span> </span>&#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> UnsupportedOperationException(</span><br><span class="line"> <span class="string">"method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getDefaultPort</span><span class="params">()</span> </span>&#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> UnsupportedOperationException(</span><br><span class="line"> <span class="string">"method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">public</span> com.alibaba.dubbo.rpc.<span class="function">Exporter <span class="title">export</span><span class="params">(</span></span></span><br><span class="line"><span class="function"><span class="params"> com.alibaba.dubbo.rpc.Invoker arg0)</span></span></span><br><span class="line"><span class="function"> <span class="keyword">throws</span> com.alibaba.dubbo.rpc.RpcException </span>&#123;</span><br><span class="line"> <span class="keyword">if</span> (arg0 == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(</span><br><span class="line"> <span class="string">"com.alibaba.dubbo.rpc.Invoker argument == null"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (arg0.getUrl() == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(</span><br><span class="line"> <span class="string">"com.alibaba.dubbo.rpc.Invoker argument getUrl() == null"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> com.alibaba.dubbo.common.URL url = arg0.getUrl();</span><br><span class="line"> String extName = ((url.getProtocol() == <span class="keyword">null</span>) ? <span class="string">"dubbo"</span></span><br><span class="line"> : url.getProtocol());</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (extName == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(</span><br><span class="line"> <span class="string">"Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("</span> +</span><br><span class="line"> url.toString() + <span class="string">") use keys([protocol])"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol<span class="class">.<span class="keyword">class</span>)</span></span><br><span class="line"><span class="class"> .<span class="title">getExtension</span>(<span class="title">extName</span>)</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> extension.export(arg0);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">public</span> com.alibaba.dubbo.rpc.<span class="function">Invoker <span class="title">refer</span><span class="params">(java.lang.Class arg0,</span></span></span><br><span class="line"><span class="function"><span class="params"> com.alibaba.dubbo.common.URL arg1)</span></span></span><br><span class="line"><span class="function"> <span class="keyword">throws</span> com.alibaba.dubbo.rpc.RpcException </span>&#123;</span><br><span class="line"> <span class="keyword">if</span> (arg1 == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(<span class="string">"url == null"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> com.alibaba.dubbo.common.URL url = arg1;</span><br><span class="line"> <span class="comment">// 其实前面所说的逻辑就在这里呈现了</span></span><br><span class="line"> String extName = ((url.getProtocol() == <span class="keyword">null</span>) ? <span class="string">"dubbo"</span></span><br><span class="line"> : url.getProtocol());</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (extName == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(</span><br><span class="line"> <span class="string">"Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("</span> +</span><br><span class="line"> url.toString() + <span class="string">") use keys([protocol])"</span>);</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="comment">// 在这就是实际的通过dubbo 的 spi 去加载实际对应的扩展</span></span><br><span class="line"> com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol<span class="class">.<span class="keyword">class</span>)</span></span><br><span class="line"><span class="class"> .<span class="title">getExtension</span>(<span class="title">extName</span>)</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> extension.refer(arg0, arg1);</span><br><span class="line"> &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>SPI全称是Service Provider Interface，咋眼看跟api是不是有点相似，api是application interface，这两个其实在某些方面有类似的地方，也有蛮大的区别，比如我们基于 dubbo 的微服务，一般我们可以提供服务，然后非泛化调用的话，我们可以把 api 包提供给应用调用方，他们根据接口签名传对应参数并配置好对应的服务发现如 zk 等就可以调用我们的服务了，然后 spi 会有点类似但是是反过来的关系，相当于是一种规范，比如我约定完成这个功能需要两个有两个接口，一个是连接的，一个是断开的，其实就可以用 jdbc 的驱动举例，比较老套了，然后各个厂家去做具体的实现吧，到时候根据我接口的全限定名的文件来加载实际的实现类，然后运行的时候调用对应实现类的方法就完了</p>
<p><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/3sKdpg.png" alt="3sKdpg"></p>
<p>看上面的图，<code>java.sql.Driver</code>就是 spi，对应在classpath 的 META-INF/services 目录下的这个文件，里边的内容就是具体的实现类</p>
<p><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/1590735097909.jpg" alt="1590735097909"></p>
<p>简单介绍了 Java的 SPI，再来说说 dubbo 的，dubbo 中为啥要用 SPI 呢，主要是为了框架的可扩展性和性能方面的考虑，比如协议层 dubbo 默认使用 dubbo 协议，同时也支持很多其他协议，也支持用户自己实现协议，那么跟 Java 的 SPI 会有什么区别呢，我们也来看个文件</p>
<p><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/bqxWMp.png" alt="bqxWMp"></p>
<p>是不是看着很想，又有点不一样，在 Java 的 SPI 配置文件里每一行只有一个实现类的全限定名，在 Dubbo的 SPI配置文件中是 key=value 的形式，我们只需要对应的 key 就能加载对应的实现，</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 返回指定名字的扩展。如果指定名字的扩展不存在，则抛异常 &#123;<span class="doctag">@link</span> IllegalStateException&#125;.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> name</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span></span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="meta">@SuppressWarnings</span>(<span class="string">"unchecked"</span>)</span><br><span class="line"> <span class="function"><span class="keyword">public</span> T <span class="title">getExtension</span><span class="params">(String name)</span> </span>&#123;</span><br><span class="line"> <span class="keyword">if</span> (name == <span class="keyword">null</span> || name.length() == <span class="number">0</span>)</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(<span class="string">"Extension name == null"</span>);</span><br><span class="line"> <span class="keyword">if</span> (<span class="string">"true"</span>.equals(name)) &#123;</span><br><span class="line"> <span class="keyword">return</span> getDefaultExtension();</span><br><span class="line"> &#125;</span><br><span class="line"> Holder&lt;Object&gt; holder = cachedInstances.get(name);</span><br><span class="line"> <span class="keyword">if</span> (holder == <span class="keyword">null</span>) &#123;</span><br><span class="line"> cachedInstances.putIfAbsent(name, <span class="keyword">new</span> Holder&lt;Object&gt;());</span><br><span class="line"> holder = cachedInstances.get(name);</span><br><span class="line"> &#125;</span><br><span class="line"> Object instance = holder.get();</span><br><span class="line"> <span class="keyword">if</span> (instance == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">synchronized</span> (holder) &#123;</span><br><span class="line"> instance = holder.get();</span><br><span class="line"> <span class="keyword">if</span> (instance == <span class="keyword">null</span>) &#123;</span><br><span class="line"> instance = createExtension(name);</span><br><span class="line"> holder.set(instance);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="keyword">return</span> (T) instance;</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
<p>这里其实就可以看出来第二个不同点了，就是这个<code>cachedInstances</code>，第一个是不用像 Java 原生的 SPI 那样去遍历加载对应的服务类，只需要通过 key 去寻找，并且寻找的时候会先从缓存的对象里去取，还有就是注意下这里的 DCL(double check lock)</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@SuppressWarnings</span>(<span class="string">"unchecked"</span>)</span><br><span class="line"> <span class="function"><span class="keyword">private</span> T <span class="title">createExtension</span><span class="params">(String name)</span> </span>&#123;</span><br><span class="line"> Class&lt;?&gt; clazz = getExtensionClasses().get(name);</span><br><span class="line"> <span class="keyword">if</span> (clazz == <span class="keyword">null</span>) &#123;</span><br><span class="line"> <span class="keyword">throw</span> findException(name);</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="keyword">try</span> &#123;</span><br><span class="line"> T instance = (T) EXTENSION_INSTANCES.get(clazz);</span><br><span class="line"> <span class="keyword">if</span> (instance == <span class="keyword">null</span>) &#123;</span><br><span class="line"> EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());</span><br><span class="line"> instance = (T) EXTENSION_INSTANCES.get(clazz);</span><br><span class="line"> &#125;</span><br><span class="line"> injectExtension(instance);</span><br><span class="line"> Set&lt;Class&lt;?&gt;&gt; wrapperClasses = cachedWrapperClasses;</span><br><span class="line"> <span class="keyword">if</span> (wrapperClasses != <span class="keyword">null</span> &amp;&amp; wrapperClasses.size() &gt; <span class="number">0</span>) &#123;</span><br><span class="line"> <span class="keyword">for</span> (Class&lt;?&gt; wrapperClass : wrapperClasses) &#123;</span><br><span class="line"> instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="keyword">return</span> instance;</span><br><span class="line"> &#125; <span class="keyword">catch</span> (Throwable t) &#123;</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalStateException(<span class="string">"Extension instance(name: "</span> + name + <span class="string">", class: "</span> +</span><br><span class="line"> type + <span class="string">") could not be instantiated: "</span> + t.getMessage(), t);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
<p>然后就是创建扩展了，这里如果 wrapperClasses 就会遍历生成wrapper实例，并做 setter 依赖注入，但是这里cachedWrapperClasses的来源还是有点搞不清楚，得再看下 com.alibaba.dubbo.common.extension.ExtensionLoader#loadFile的具体逻辑<br>又看了遍新的代码，这个函数被抽出来了</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * test if clazz is a wrapper class</span></span><br><span class="line"><span class="comment"> * &lt;p&gt;</span></span><br><span class="line"><span class="comment"> * which has Constructor with given class type as its only argument</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">private</span> <span class="keyword">boolean</span> <span class="title">isWrapperClass</span><span class="params">(Class&lt;?&gt; clazz)</span> </span>&#123;</span><br><span class="line"> <span class="keyword">try</span> &#123;</span><br><span class="line"> clazz.getConstructor(type);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> &#125; <span class="keyword">catch</span> (NoSuchMethodException e) &#123;</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
<p>是否是 wrapperClass 其实就看构造函数的。</p>
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<p>因为传说中的出身问题，我以前写的是PHP，在使用 swoole 之前，基本的应用调试手段就是简单粗暴的 var_dump，exit，对于单进程模型的 PHP 也是简单有效，技术栈换成 Java 之后，就变得没那么容易，一方面是需要编译，另一方面是一般都是基于 spring 的项目，如果问题定位比较模糊，那框架层的是很难靠简单的 System.out.println 或者打 log 解决，(PS：我觉得可能我写的东西比较适合从 PHP 这种弱类型语言转到 Java 的小白同学)这个时候一方面因为是 Java，有了非常好用的 idea IDE 的支持，可以各种花式调试，条件断点尤其牛叉，但是又因为有 Spring+Java 的双重原因，有些情况下单步调试可以把手按废掉，这也是我之前一直比较困惑苦逼的点，后来随着慢慢精（jiang）进（you）之后，比如对于一个 oom 的情况，我们可以通过启动参数加上-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=xx/xx 来配置溢出时的堆dump 日志，获取到这个文件后，我们可以通过像 Memory Analyzer (MAT)[<a href="https://www.eclipse.org/mat/]" target="_blank" rel="noopener">https://www.eclipse.org/mat/]</a> (The Eclipse Memory Analyzer is a fast and feature-rich Java heap analyzer that helps you find memory leaks and reduce memory consumption.)来查看诊断问题所在，之前用到的时候是因为有个死循环一直往链表里塞数据，属于比较简单的，后来一次是由于运维进行应用迁移时按默认的统一配置了堆内存大小，导致内存的确不够用，所以溢出了，<br>今天想说的其实主要是我们的 thread dump，这也是我最近才真正用的一个方法，可能真的很小白了，用过 ide 的单步调试其实都知道会有一个一层层的玩意，比如函数从 A，调用了 B，再从 B 调用了 C，一直往下(因为是 Java，所以还有很多🤦‍♂️)，这个其实也是大部分语言的调用模型，利用了栈这个数据结构，通过这个结构我们可以知道代码的调用链路，由于对于一个 spring 应用，在本身框架代码量非常庞大的情况下，外加如果应用代码也是非常多的时候，有时候通过单步调试真的很难短时间定位到问题，需要非常大的耐心和仔细观察，当然不是说完全不行，举个例子当我的应用经常启动需要非常长的时间，因为本身应用有非常多个 bean，比较难说究竟是 bean 的加载的确很慢还是有什么异常原因，这种时候就可以使用 thread dump 了，具体怎么操作呢<br><img data-src="https://mystore-1255223546.cos.ap-chengdu.myqcloud.com/uPic/GPYHjd.png" alt=""><br>如果在idea 中运行或者调试时，可以直接点击这个照相机一样的按钮，右边就会出现了左边会显示所有的线程，右边会显示线程栈，</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">&quot;main@1&quot; prio&#x3D;5 tid&#x3D;0x1 nid&#x3D;NA runnable</span><br><span class="line"> java.lang.Thread.State: RUNNABLE</span><br><span class="line"> at TreeDistance.treeDist(TreeDistance.java:64)</span><br><span class="line"> at TreeDistance.treeDist(TreeDistance.java:65)</span><br><span class="line"> at TreeDistance.treeDist(TreeDistance.java:65)</span><br><span class="line"> at TreeDistance.treeDist(TreeDistance.java:65)</span><br><span class="line"> at TreeDistance.main(TreeDistance.java:45)</span><br></pre></td></tr></table></figure>
<p>这就是我们主线程的堆栈信息了，main 表示这个线程名，prio表示优先级，默认是 5，tid 表示线程 id，nid 表示对应的系统线程，后面的runnable 表示目前线程状态，因为是被我打了断点，所以是就许状态，然后下面就是对应的线程栈内容了，在<code>TreeDistance</code>类的 <code>treeDist</code>方法中，对应的文件行数是 64 行。<br>这里使用 thread dump一般也不会是上面我截图代码里的这种代码量很少的，一般是大型项目，有时候跑着跑着没反应，又不知道跑到哪了，特别是一些刚接触的大项目或者需要定位一个大项目的一个疑难问题，一时没思路时，可以使用这个方法，个人觉得非常有帮助。</p>
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return fetch(`${api_server}/1.1${url}`, {
method,
headers: {
'X-LC-Id' : app_id,
'X-LC-Key' : app_key,
'Content-Type': 'application/json',
},
body: JSON.stringify(data)
});
};
if (CONFIG.page.isPost) {
if (CONFIG.hostname !== location.hostname) return;
addCount(Counter);
} else if (document.querySelectorAll('.post-title-link').length >= 1) {
showTime(Counter);
}
}
let api_server = app_id.slice(-9) !== '-MdYXbMMI' ? server_url : `https://${app_id.slice(0, 8).toLowerCase()}.api.lncldglobal.com`;
if (api_server) {
fetchData(api_server);
} else {
fetch('https://app-router.leancloud.cn/2/route?appId=' + app_id)
.then(response => response.json())
.then(({ api_server }) => {
fetchData('https://' + api_server);
});
}
})();
</script>
</div>
</footer>
</div>
<script src="/lib/anime.min.js"></script>
<script src="//cdn.jsdelivr.net/npm/jquery@3/dist/jquery.min.js"></script>
<script src="//cdn.jsdelivr.net/gh/fancyapps/fancybox@3/dist/jquery.fancybox.min.js"></script>
<script src="//cdn.jsdelivr.net/npm/lozad@1/dist/lozad.min.js"></script>
<script src="/lib/velocity/velocity.min.js"></script>
<script src="/lib/velocity/velocity.ui.min.js"></script>
<script src="/js/utils.js"></script>
<script src="/js/motion.js"></script>
<script src="/js/schemes/pisces.js"></script>
<script src="/js/next-boot.js"></script>
<script>
(function(){
var canonicalURL, curProtocol;
//Get the <link> tag
var x=document.getElementsByTagName("link");
//Find the last canonical URL
if(x.length > 0){
for (i=0;i<x.length;i++){
if(x[i].rel.toLowerCase() == 'canonical' && x[i].href){
canonicalURL=x[i].href;
}
}
}
//Get protocol
if (!canonicalURL){
curProtocol = window.location.protocol.split(':')[0];
}
else{
curProtocol = canonicalURL.split(':')[0];
}
//Get current URL if the canonical URL does not exist
if (!canonicalURL) canonicalURL = window.location.href;
//Assign script content. Replace current URL with the canonical URL
!function(){var e=/([http|https]:\/\/[a-zA-Z0-9\_\.]+\.baidu\.com)/gi,r=canonicalURL,t=document.referrer;if(!e.test(r)){var n=(String(curProtocol).toLowerCase() === 'https')?"https://sp0.baidu.com/9_Q4simg2RQJ8t7jm9iCKT-xh_/s.gif":"//api.share.baidu.com/s.gif";t?(n+="?r="+encodeURIComponent(document.referrer),r&&(n+="&l="+r)):r&&(n+="?l="+r);var i=new Image;i.src=n}}(window);})();
</script>
<script>
function loadCount() {
var d = document, s = d.createElement('script');
s.src = 'https://nicksxs.disqus.com/count.js';
s.id = 'dsq-count-scr';
(d.head || d.body).appendChild(s);
}
// defer loading until the whole page loading is completed
window.addEventListener('load', loadCount, false);
</script>
</body>
</html>