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653 lines
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653 lines
130 KiB
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class="tag-list-count">1</span></li><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><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><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><li class="tag-list-item"><a class="tag-list-link" href="/tags/java/" rel="tag">java</a><span class="tag-list-count">19</span></li><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><li class="tag-list-item"><a class="tag-list-link" href="/tags/leetcode/" rel="tag">leetcode</a><span class="tag-list-count">28</span></li><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><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><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><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><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><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><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><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><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><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><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><li class="tag-list-item"><a class="tag-list-link" href="/tags/nginx/" rel="tag">nginx</a><span class="tag-list-count">1</span></li><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><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><li class="tag-list-item"><a class="tag-list-link" href="/tags/php/" rel="tag">php</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/procedure/" rel="tag">procedure</a><span 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class="tag-list-link" href="/tags/stack/" rel="tag">stack</a><span class="tag-list-count">1</span></li><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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><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">6</span></li><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><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><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><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><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><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><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><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><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><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><li class="tag-list-item"><a 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class="tag-list-count">1</span></li><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><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><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AE%89%E5%85%A8/" rel="tag">安全</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AE%B9%E9%94%99%E6%9C%BA%E5%88%B6/" rel="tag">容错机制</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%AF%84%E7%94%9F%E8%99%AB/" rel="tag">寄生虫</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B0%84%E5%87%BB/" rel="tag">射击</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B0%8F%E6%8A%80%E5%B7%A7/" rel="tag">小技巧</a><span class="tag-list-count">5</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B1%80%E5%8F%A3%E8%A1%97/" rel="tag">局口街</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B8%83%E9%9A%86%E8%BF%87%E6%BB%A4%E5%99%A8/" rel="tag">布隆过滤器</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B2%E6%B4%BB/" rel="tag">干活</a><span class="tag-list-count">5</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B4%E4%B8%AD%E6%80%BB%E7%BB%93/" rel="tag">年中总结</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B4%E7%BB%88%E6%80%BB%E7%BB%93/" rel="tag">年终总结</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B6%E5%8F%91/" rel="tag">并发</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%B8%E7%A6%8F%E4%BA%86%E5%90%97/" rel="tag">幸福了吗</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%B9%BB%E8%AF%BB/" rel="tag">幻读</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BA%94%E7%94%A8/" rel="tag">应用</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BC%80%E8%BD%A6/" rel="tag">开车</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BC%B1%E5%BC%95%E7%94%A8/" rel="tag">弱引用</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E5%BD%B1%E8%AF%84/" rel="tag">影评</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%89%80%E6%9C%89%E6%9D%83/" rel="tag">所有权</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%89%93%E5%8D%A1/" rel="tag">打卡</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%89%B6%E6%A2%AF/" rel="tag">扶梯</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8A%80%E6%9C%AF/" rel="tag">技术</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%8B%96%E6%9B%B4/" rel="tag">拖更</a><span class="tag-list-count">2</span></li><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><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><li class="tag-list-item"><a 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itemprop="name headline"><a href="/2019/12/10/Redis-Part-1/" class="post-title-link" itemprop="url">Redis_分布式锁</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 title="创建时间：2019-12-10 23:26:26" itemprop="dateCreated datePublished" datetime="2019-12-10T23:26:26+08:00">2019-12-10</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/Distributed-Lock/" itemprop="url" rel="index"><span itemprop="name">Distributed Lock</span></a> </span>， <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/C/" itemprop="url" rel="index"><span itemprop="name">C</span></a> </span>， <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/C/Redis/" itemprop="url" rel="index"><span itemprop="name">Redis</span></a> </span></span><span id="/2019/12/10/Redis-Part-1/" class="post-meta-item leancloud_visitors" data-flag-title="Redis_分布式锁" 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 title="disqus" href="/2019/12/10/Redis-Part-1/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2019/12/10/Redis-Part-1/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>今天看了一下 <code>redis</code> 分布式锁 <code>redlock</code> 的实现，简单记录下，</p><h2 id="加锁"><a href="#加锁" class="headerlink" title="加锁"></a>加锁</h2><p>原先我对 <code>redis</code> 锁的概念就是加锁使用 <code>setnx</code>，解锁使用 <code>lua</code> 脚本，但是 <code>setnx</code> 具体是啥，<code>lua</code> 脚本是啥不是很清楚<br>首先简单思考下这个问题，首先为啥不是先 <code>get</code> 一下 <code>key</code> 存不存在，然后再 <code>set</code> 一个 <code>key value</code>，因为加锁这个操作我们是要保证两点，一个是不能中途被打断，也就是说要原子性，如果是先 <code>get</code> 一下 <code>key</code>，如果不存在再 <code>set</code> 值的话，那就不是原子操作了；第二个是可不可以直接 <code>set</code> 值呢，显然不行，锁要保证唯一性，有且只能有一个线程或者其他应用单位获得该锁，正好 <code>setnx</code> 给了我们这种原子命令</p><p>然后是 <code>setnx</code> 的键和值分别是啥，键比较容易想到是要锁住的资源，比如 <code>user_id</code>, 这里有个我自己之前比较容易陷进去的误区，但是这个误区后<br>面再说，这里其实是把<code>user_id</code> 作为要锁住的资源，在我获得锁的时候别的线程不允许操作，以此保证业务的正确性，不会被多个线程同时修改，确定了键，再来看看值是啥，其实原先我认为值是啥都没关系，我只要锁住了，光键就够我用了，但是考虑下多个线程的问题，如果我这个线程加了锁，然后我因为 <code>gc</code> 停顿等原因卡死了，这个时候<code>redis</code> 的锁或者说就是 <code>redis</code> 的缓存已经过期了，这时候另一个线程获得锁成功，然后我这个线程又活过来了，然后我就仍然认为我拿着锁，我去对数据进行修改或者释放锁，是不是就出现问题了，所以是不是我们还需要一个东西来区分这个锁是哪个线程加的，所以我们可以将值设置成为一个线程独有识别的值，至少在相对长的一段时间内不会重复。</p><p>上面其实还有两个问题，一个是当 <code>gc</code> 超时时，我这个线程如何知道我手里的锁已经过期了，一种方法是我在加好锁之后就维护一个超时时间，这里其实还有个问题，不过跟第二个问题相关，就一起说了，就是设置超时时间，有些对于不是锁的 <code>redis</code> 缓存操作可以是先设置好值，然后在设置过期时间，那么这就又有上面说到的不是原子性的问题，那么就需要在同一条指令里把超时时间也设置了，幸好 <code>redis</code> 提供了这种支持</p><pre class="line-numbers language-none"><code class="language-none">SET resource_name my_random_value NX PX 30000<span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><p>这里借鉴一下解释下，<code>resource_name</code>就是 key，代表要锁住的东西，<code>my_random_value</code>就是识别我这个线程的，<code>NX</code>代表只有在不存在的时候才设置，然后<code>PX 30000</code>表示超时时间是 30秒自动过期</p><p>PS：记录下我原先有的一个误区，是不是要用 key 来区分加锁的线程，这样只有一个用处，就是自身线程可以识别是否是自己加的锁，但是最大的问题是别的线程不知道，其实这个用户的出发点是我在担心前面提过的一个问题，就是当 gc 停顿后，我要去判断当前的这个锁是否是我加的，还有就是当释放锁的时候，如果保证不会错误释放了其他线程加的锁，但是这样附带很多其他问题，最大的就是其他线程怎么知道能不能加这个锁。</p><h2 id="解锁"><a href="#解锁" class="headerlink" title="解锁"></a>解锁</h2><p>当线程在锁过期之前就处理完了业务逻辑，那就可以提前释放这个锁，那么提前释放要怎么操作，直接<code>del key</code>显然是不行的，因为这样就是我前面想用线程随机值加资源名作为锁的初衷，我不能去释放别的线程加的锁，那么我要怎么办呢，先 <code>get</code> 一下看是不是我的？那又变成非原子的操作了，幸好redis 也考虑到了这个问题，给了<code>lua</code> 脚本来操作这种</p><pre class="line-numbers language-lua" data-language="lua"><code class="language-lua"><span class="token keyword">if</span> redis<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token string">"get"</span><span class="token punctuation">,</span>KEYS<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token operator">==</span> ARGV<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token keyword">then</span>
|
|
<span class="token keyword">return</span> redis<span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span><span class="token string">"del"</span><span class="token punctuation">,</span>KEYS<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
|
|
<span class="token keyword">else</span>
|
|
<span class="token keyword">return</span> <span class="token number">0</span>
|
|
<span class="token keyword">end</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>这里的<code>KEYS[1]</code>就是前面加锁的<code>resource_name</code>,<code>ARGV[1]</code>就是线程的随机值<code>my_random_value</code></p><h2 id="多节点"><a href="#多节点" class="headerlink" title="多节点"></a>多节点</h2><p>前面说的其实是单节点 <code>redis</code> 作为分布式锁的情况，那么当我们的 <code>redis</code> 有多节点的情况呢，如果多节点下处于加锁或者解锁或者锁有效情况下<br><code>redis</code> 的某个节点宕掉了怎么办，这里就有一些需要思考的地方，是否单独搞一个单节点的 <code>redis</code>作为分布式锁专用的，但是如果这个单节点的挂了呢，还有就是成本问题，所以我们需要一个多节点的分布式锁方案<br>这里就引出了开头说到的<code>redlock</code>，这个可是 <code>redis</code>的作者写的, 他的加锁过程是分以下几步去做这个事情</p><ul><li>获取当前时间（毫秒数）。</li><li>按顺序依次向N个Redis节点执行获取锁的操作。这个获取操作跟前面基于单Redis节点的获取锁的过程相同，包含随机字符串my_random_value，也包含过期时间(比如PX 30000，即锁的有效时间)。为了保证在某个Redis节点不可用的时候算法能够继续运行，这个获取锁的操作还有一个超时时间(time out)，它要远小于锁的有效时间（几十毫秒量级）。客户端在向某个Redis节点获取锁失败以后，应该立即尝试下一个Redis节点。这里的失败，应该包含任何类型的失败，比如该Redis节点不可用，或者该Redis节点上的锁已经被其它客户端持有（注：Redlock原文中这里只提到了Redis节点不可用的情况，但也应该包含其它的失败情况）。</li><li>计算整个获取锁的过程总共消耗了多长时间，计算方法是用当前时间减去第1步记录的时间。如果客户端从大多数Redis节点（>= N/2+1）成功获取到了锁，并且获取锁总共消耗的时间没有超过锁的有效时间(lock validity time)，那么这时客户端才认为最终获取锁成功；否则，认为最终获取锁失败。</li><li>如果最终获取锁成功了，那么这个锁的有效时间应该重新计算，它等于最初的锁的有效时间减去第3步计算出来的获取锁消耗的时间。</li><li>如果最终获取锁失败了（可能由于获取到锁的Redis节点个数少于N/2+1，或者整个获取锁的过程消耗的时间超过了锁的最初有效时间），那么客户端应该立即向所有Redis节点发起释放锁的操作（即前面介绍的Redis Lua脚本）。<br>释放锁的过程比较简单：客户端向所有Redis节点发起释放锁的操作，不管这些节点当时在获取锁的时候成功与否。这里为什么要向所有的节点发送释放锁的操作呢，这里是因为有部分的节点的失败原因可能是加锁时阻塞，加锁成功的结果没有及时返回，所以为了防止这种情况还是需要向所有发起这个释放锁的操作。<br>初步记录就先到这。</li></ul></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2019/12/07/JVM-G1-Part-1/"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="image" content="/uploads/avatar.jpg"><meta itemprop="name" content="Nicksxs"><meta itemprop="description" content="learn from zero,技术博客，Nicksxs，史学森"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="Nicksxs's Blog"></span><header class="post-header"><h2 class="post-title" itemprop="name headline"><a href="/2019/12/07/JVM-G1-Part-1/" class="post-title-link" itemprop="url">JVM源码分析之G1垃圾收集器分析一</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 title="创建时间：2019-12-07 00:54:19" itemprop="dateCreated datePublished" datetime="2019-12-07T00:54:19+08:00">2019-12-07</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：2019-12-20 00:01:42" itemprop="dateModified" datetime="2019-12-20T00:01:42+08:00">2019-12-20</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/JVM/" itemprop="url" rel="index"><span itemprop="name">JVM</span></a> </span>， <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/Java/GC/" itemprop="url" rel="index"><span itemprop="name">GC</span></a> </span>， <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/C/" itemprop="url" rel="index"><span itemprop="name">C++</span></a> </span></span><span id="/2019/12/07/JVM-G1-Part-1/" class="post-meta-item leancloud_visitors" data-flag-title="JVM源码分析之G1垃圾收集器分析一" 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 title="disqus" href="/2019/12/07/JVM-G1-Part-1/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2019/12/07/JVM-G1-Part-1/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>对 Java 的 gc 实现比较感兴趣，原先一般都是看周志明的书，但其实并没有讲具体的 gc 源码，而是把整个思路和流程讲解了一下<br>特别是 G1 的具体实现<br>一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存，简而言之，就是原先对新生代老年代的收集会涉及到整个代的堆内存空间，而G1 把它变成了更细致的小块内存<br>这带来了一个很明显的好处和一个很明显的坏处，好处是内存收集可以更灵活，耗时会变短，但整个收集的处理复杂度就变高了<br>目前看了一点点关于 G1 收集的预期时间相关的代码</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">HeapWord* G1CollectedHeap::do_collection_pause(size_t word_size,
|
|
uint gc_count_before,
|
|
bool* succeeded,
|
|
GCCause::Cause gc_cause) {
|
|
assert_heap_not_locked_and_not_at_safepoint();
|
|
VM_G1CollectForAllocation op(word_size,
|
|
gc_count_before,
|
|
gc_cause,
|
|
false, /* should_initiate_conc_mark */
|
|
g1_policy()->max_pause_time_ms());
|
|
VMThread::execute(&op);
|
|
|
|
HeapWord* result = op.result();
|
|
bool ret_succeeded = op.prologue_succeeded() && op.pause_succeeded();
|
|
assert(result == NULL || ret_succeeded,
|
|
"the result should be NULL if the VM did not succeed");
|
|
*succeeded = ret_succeeded;
|
|
|
|
assert_heap_not_locked();
|
|
return result;
|
|
}<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></code></pre><p>这里就是收集时需要停顿的，其中<code>VMThread::execute(&op);</code>是具体执行的，真正执行的是<code>VM_G1CollectForAllocation::doit</code>方法</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">void VM_G1CollectForAllocation::doit() {
|
|
G1CollectedHeap* g1h = G1CollectedHeap::heap();
|
|
assert(!_should_initiate_conc_mark || g1h->should_do_concurrent_full_gc(_gc_cause),
|
|
"only a GC locker, a System.gc(), stats update, whitebox, or a hum allocation induced GC should start a cycle");
|
|
|
|
if (_word_size > 0) {
|
|
// An allocation has been requested. So, try to do that first.
|
|
_result = g1h->attempt_allocation_at_safepoint(_word_size,
|
|
false /* expect_null_cur_alloc_region */);
|
|
if (_result != NULL) {
|
|
// If we can successfully allocate before we actually do the
|
|
// pause then we will consider this pause successful.
|
|
_pause_succeeded = true;
|
|
return;
|
|
}
|
|
}
|
|
|
|
GCCauseSetter x(g1h, _gc_cause);
|
|
if (_should_initiate_conc_mark) {
|
|
// It's safer to read old_marking_cycles_completed() here, given
|
|
// that noone else will be updating it concurrently. Since we'll
|
|
// only need it if we're initiating a marking cycle, no point in
|
|
// setting it earlier.
|
|
_old_marking_cycles_completed_before = g1h->old_marking_cycles_completed();
|
|
|
|
// At this point we are supposed to start a concurrent cycle. We
|
|
// will do so if one is not already in progress.
|
|
bool res = g1h->g1_policy()->force_initial_mark_if_outside_cycle(_gc_cause);
|
|
|
|
// The above routine returns true if we were able to force the
|
|
// next GC pause to be an initial mark; it returns false if a
|
|
// marking cycle is already in progress.
|
|
//
|
|
// If a marking cycle is already in progress just return and skip the
|
|
// pause below - if the reason for requesting this initial mark pause
|
|
// was due to a System.gc() then the requesting thread should block in
|
|
// doit_epilogue() until the marking cycle is complete.
|
|
//
|
|
// If this initial mark pause was requested as part of a humongous
|
|
// allocation then we know that the marking cycle must just have
|
|
// been started by another thread (possibly also allocating a humongous
|
|
// object) as there was no active marking cycle when the requesting
|
|
// thread checked before calling collect() in
|
|
// attempt_allocation_humongous(). Retrying the GC, in this case,
|
|
// will cause the requesting thread to spin inside collect() until the
|
|
// just started marking cycle is complete - which may be a while. So
|
|
// we do NOT retry the GC.
|
|
if (!res) {
|
|
assert(_word_size == 0, "Concurrent Full GC/Humongous Object IM shouldn't be allocating");
|
|
if (_gc_cause != GCCause::_g1_humongous_allocation) {
|
|
_should_retry_gc = true;
|
|
}
|
|
return;
|
|
}
|
|
}
|
|
|
|
// Try a partial collection of some kind.
|
|
_pause_succeeded = g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);
|
|
|
|
if (_pause_succeeded) {
|
|
if (_word_size > 0) {
|
|
// An allocation had been requested. Do it, eventually trying a stronger
|
|
// kind of GC.
|
|
_result = g1h->satisfy_failed_allocation(_word_size, &_pause_succeeded);
|
|
} else {
|
|
bool should_upgrade_to_full = !g1h->should_do_concurrent_full_gc(_gc_cause) &&
|
|
!g1h->has_regions_left_for_allocation();
|
|
if (should_upgrade_to_full) {
|
|
// There has been a request to perform a GC to free some space. We have no
|
|
// information on how much memory has been asked for. In case there are
|
|
// absolutely no regions left to allocate into, do a maximally compacting full GC.
|
|
log_info(gc, ergo)("Attempting maximally compacting collection");
|
|
_pause_succeeded = g1h->do_full_collection(false, /* explicit gc */
|
|
true /* clear_all_soft_refs */);
|
|
}
|
|
}
|
|
guarantee(_pause_succeeded, "Elevated collections during the safepoint must always succeed.");
|
|
} else {
|
|
assert(_result == NULL, "invariant");
|
|
// The only reason for the pause to not be successful is that, the GC locker is
|
|
// active (or has become active since the prologue was executed). In this case
|
|
// we should retry the pause after waiting for the GC locker to become inactive.
|
|
_should_retry_gc = true;
|
|
}
|
|
}<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></code></pre><p>这里可以看到核心的是<code>G1CollectedHeap::do_collection_pause_at_safepoint</code>这个方法，它带上了目标暂停时间的值</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
|
|
assert_at_safepoint_on_vm_thread();
|
|
guarantee(!is_gc_active(), "collection is not reentrant");
|
|
|
|
if (GCLocker::check_active_before_gc()) {
|
|
return false;
|
|
}
|
|
|
|
_gc_timer_stw->register_gc_start();
|
|
|
|
GCIdMark gc_id_mark;
|
|
_gc_tracer_stw->report_gc_start(gc_cause(), _gc_timer_stw->gc_start());
|
|
|
|
SvcGCMarker sgcm(SvcGCMarker::MINOR);
|
|
ResourceMark rm;
|
|
|
|
g1_policy()->note_gc_start();
|
|
|
|
wait_for_root_region_scanning();
|
|
|
|
print_heap_before_gc();
|
|
print_heap_regions();
|
|
trace_heap_before_gc(_gc_tracer_stw);
|
|
|
|
_verifier->verify_region_sets_optional();
|
|
_verifier->verify_dirty_young_regions();
|
|
|
|
// We should not be doing initial mark unless the conc mark thread is running
|
|
if (!_cm_thread->should_terminate()) {
|
|
// This call will decide whether this pause is an initial-mark
|
|
// pause. If it is, in_initial_mark_gc() will return true
|
|
// for the duration of this pause.
|
|
g1_policy()->decide_on_conc_mark_initiation();
|
|
}
|
|
|
|
// We do not allow initial-mark to be piggy-backed on a mixed GC.
|
|
assert(!collector_state()->in_initial_mark_gc() ||
|
|
collector_state()->in_young_only_phase(), "sanity");
|
|
|
|
// We also do not allow mixed GCs during marking.
|
|
assert(!collector_state()->mark_or_rebuild_in_progress() || collector_state()->in_young_only_phase(), "sanity");
|
|
|
|
// Record whether this pause is an initial mark. When the current
|
|
// thread has completed its logging output and it's safe to signal
|
|
// the CM thread, the flag's value in the policy has been reset.
|
|
bool should_start_conc_mark = collector_state()->in_initial_mark_gc();
|
|
|
|
// Inner scope for scope based logging, timers, and stats collection
|
|
{
|
|
EvacuationInfo evacuation_info;
|
|
|
|
if (collector_state()->in_initial_mark_gc()) {
|
|
// We are about to start a marking cycle, so we increment the
|
|
// full collection counter.
|
|
increment_old_marking_cycles_started();
|
|
_cm->gc_tracer_cm()->set_gc_cause(gc_cause());
|
|
}
|
|
|
|
_gc_tracer_stw->report_yc_type(collector_state()->yc_type());
|
|
|
|
GCTraceCPUTime tcpu;
|
|
|
|
G1HeapVerifier::G1VerifyType verify_type;
|
|
FormatBuffer<> gc_string("Pause Young ");
|
|
if (collector_state()->in_initial_mark_gc()) {
|
|
gc_string.append("(Concurrent Start)");
|
|
verify_type = G1HeapVerifier::G1VerifyConcurrentStart;
|
|
} else if (collector_state()->in_young_only_phase()) {
|
|
if (collector_state()->in_young_gc_before_mixed()) {
|
|
gc_string.append("(Prepare Mixed)");
|
|
} else {
|
|
gc_string.append("(Normal)");
|
|
}
|
|
verify_type = G1HeapVerifier::G1VerifyYoungNormal;
|
|
} else {
|
|
gc_string.append("(Mixed)");
|
|
verify_type = G1HeapVerifier::G1VerifyMixed;
|
|
}
|
|
GCTraceTime(Info, gc) tm(gc_string, NULL, gc_cause(), true);
|
|
|
|
uint active_workers = AdaptiveSizePolicy::calc_active_workers(workers()->total_workers(),
|
|
workers()->active_workers(),
|
|
Threads::number_of_non_daemon_threads());
|
|
active_workers = workers()->update_active_workers(active_workers);
|
|
log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers()->total_workers());
|
|
|
|
TraceCollectorStats tcs(g1mm()->incremental_collection_counters());
|
|
TraceMemoryManagerStats tms(&_memory_manager, gc_cause(),
|
|
collector_state()->yc_type() == Mixed /* allMemoryPoolsAffected */);
|
|
|
|
G1HeapTransition heap_transition(this);
|
|
size_t heap_used_bytes_before_gc = used();
|
|
|
|
// Don't dynamically change the number of GC threads this early. A value of
|
|
// 0 is used to indicate serial work. When parallel work is done,
|
|
// it will be set.
|
|
|
|
{ // Call to jvmpi::post_class_unload_events must occur outside of active GC
|
|
IsGCActiveMark x;
|
|
|
|
gc_prologue(false);
|
|
|
|
if (VerifyRememberedSets) {
|
|
log_info(gc, verify)("[Verifying RemSets before GC]");
|
|
VerifyRegionRemSetClosure v_cl;
|
|
heap_region_iterate(&v_cl);
|
|
}
|
|
|
|
_verifier->verify_before_gc(verify_type);
|
|
|
|
_verifier->check_bitmaps("GC Start");
|
|
|
|
#if COMPILER2_OR_JVMCI
|
|
DerivedPointerTable::clear();
|
|
#endif
|
|
|
|
// Please see comment in g1CollectedHeap.hpp and
|
|
// G1CollectedHeap::ref_processing_init() to see how
|
|
// reference processing currently works in G1.
|
|
|
|
// Enable discovery in the STW reference processor
|
|
_ref_processor_stw->enable_discovery();
|
|
|
|
{
|
|
// We want to temporarily turn off discovery by the
|
|
// CM ref processor, if necessary, and turn it back on
|
|
// on again later if we do. Using a scoped
|
|
// NoRefDiscovery object will do this.
|
|
NoRefDiscovery no_cm_discovery(_ref_processor_cm);
|
|
|
|
// Forget the current alloc region (we might even choose it to be part
|
|
// of the collection set!).
|
|
_allocator->release_mutator_alloc_region();
|
|
|
|
// This timing is only used by the ergonomics to handle our pause target.
|
|
// It is unclear why this should not include the full pause. We will
|
|
// investigate this in CR 7178365.
|
|
//
|
|
// Preserving the old comment here if that helps the investigation:
|
|
//
|
|
// The elapsed time induced by the start time below deliberately elides
|
|
// the possible verification above.
|
|
double sample_start_time_sec = os::elapsedTime();
|
|
|
|
g1_policy()->record_collection_pause_start(sample_start_time_sec);
|
|
|
|
if (collector_state()->in_initial_mark_gc()) {
|
|
concurrent_mark()->pre_initial_mark();
|
|
}
|
|
|
|
g1_policy()->finalize_collection_set(target_pause_time_ms, &_survivor);
|
|
|
|
evacuation_info.set_collectionset_regions(collection_set()->region_length());
|
|
|
|
// Make sure the remembered sets are up to date. This needs to be
|
|
// done before register_humongous_regions_with_cset(), because the
|
|
// remembered sets are used there to choose eager reclaim candidates.
|
|
// If the remembered sets are not up to date we might miss some
|
|
// entries that need to be handled.
|
|
g1_rem_set()->cleanupHRRS();
|
|
|
|
register_humongous_regions_with_cset();
|
|
|
|
assert(_verifier->check_cset_fast_test(), "Inconsistency in the InCSetState table.");
|
|
|
|
// We call this after finalize_cset() to
|
|
// ensure that the CSet has been finalized.
|
|
_cm->verify_no_cset_oops();
|
|
|
|
if (_hr_printer.is_active()) {
|
|
G1PrintCollectionSetClosure cl(&_hr_printer);
|
|
_collection_set.iterate(&cl);
|
|
}
|
|
|
|
// Initialize the GC alloc regions.
|
|
_allocator->init_gc_alloc_regions(evacuation_info);
|
|
|
|
G1ParScanThreadStateSet per_thread_states(this, workers()->active_workers(), collection_set()->young_region_length());
|
|
pre_evacuate_collection_set();
|
|
|
|
// Actually do the work...
|
|
evacuate_collection_set(&per_thread_states);
|
|
|
|
post_evacuate_collection_set(evacuation_info, &per_thread_states);
|
|
|
|
const size_t* surviving_young_words = per_thread_states.surviving_young_words();
|
|
free_collection_set(&_collection_set, evacuation_info, surviving_young_words);
|
|
|
|
eagerly_reclaim_humongous_regions();
|
|
|
|
record_obj_copy_mem_stats();
|
|
_survivor_evac_stats.adjust_desired_plab_sz();
|
|
_old_evac_stats.adjust_desired_plab_sz();
|
|
|
|
double start = os::elapsedTime();
|
|
start_new_collection_set();
|
|
g1_policy()->phase_times()->record_start_new_cset_time_ms((os::elapsedTime() - start) * 1000.0);
|
|
|
|
if (evacuation_failed()) {
|
|
set_used(recalculate_used());
|
|
if (_archive_allocator != NULL) {
|
|
_archive_allocator->clear_used();
|
|
}
|
|
for (uint i = 0; i < ParallelGCThreads; i++) {
|
|
if (_evacuation_failed_info_array[i].has_failed()) {
|
|
_gc_tracer_stw->report_evacuation_failed(_evacuation_failed_info_array[i]);
|
|
}
|
|
}
|
|
} else {
|
|
// The "used" of the the collection set have already been subtracted
|
|
// when they were freed. Add in the bytes evacuated.
|
|
increase_used(g1_policy()->bytes_copied_during_gc());
|
|
}
|
|
|
|
if (collector_state()->in_initial_mark_gc()) {
|
|
// We have to do this before we notify the CM threads that
|
|
// they can start working to make sure that all the
|
|
// appropriate initialization is done on the CM object.
|
|
concurrent_mark()->post_initial_mark();
|
|
// Note that we don't actually trigger the CM thread at
|
|
// this point. We do that later when we're sure that
|
|
// the current thread has completed its logging output.
|
|
}
|
|
|
|
allocate_dummy_regions();
|
|
|
|
_allocator->init_mutator_alloc_region();
|
|
|
|
{
|
|
size_t expand_bytes = _heap_sizing_policy->expansion_amount();
|
|
if (expand_bytes > 0) {
|
|
size_t bytes_before = capacity();
|
|
// No need for an ergo logging here,
|
|
// expansion_amount() does this when it returns a value > 0.
|
|
double expand_ms;
|
|
if (!expand(expand_bytes, _workers, &expand_ms)) {
|
|
// We failed to expand the heap. Cannot do anything about it.
|
|
}
|
|
g1_policy()->phase_times()->record_expand_heap_time(expand_ms);
|
|
}
|
|
}
|
|
|
|
// We redo the verification but now wrt to the new CSet which
|
|
// has just got initialized after the previous CSet was freed.
|
|
_cm->verify_no_cset_oops();
|
|
|
|
// This timing is only used by the ergonomics to handle our pause target.
|
|
// It is unclear why this should not include the full pause. We will
|
|
// investigate this in CR 7178365.
|
|
double sample_end_time_sec = os::elapsedTime();
|
|
double pause_time_ms = (sample_end_time_sec - sample_start_time_sec) * MILLIUNITS;
|
|
size_t total_cards_scanned = g1_policy()->phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanRS, G1GCPhaseTimes::ScanRSScannedCards);
|
|
g1_policy()->record_collection_pause_end(pause_time_ms, total_cards_scanned, heap_used_bytes_before_gc);
|
|
|
|
evacuation_info.set_collectionset_used_before(collection_set()->bytes_used_before());
|
|
evacuation_info.set_bytes_copied(g1_policy()->bytes_copied_during_gc());
|
|
|
|
if (VerifyRememberedSets) {
|
|
log_info(gc, verify)("[Verifying RemSets after GC]");
|
|
VerifyRegionRemSetClosure v_cl;
|
|
heap_region_iterate(&v_cl);
|
|
}
|
|
|
|
_verifier->verify_after_gc(verify_type);
|
|
_verifier->check_bitmaps("GC End");
|
|
|
|
assert(!_ref_processor_stw->discovery_enabled(), "Postcondition");
|
|
_ref_processor_stw->verify_no_references_recorded();
|
|
|
|
// CM reference discovery will be re-enabled if necessary.
|
|
}
|
|
|
|
#ifdef TRACESPINNING
|
|
ParallelTaskTerminator::print_termination_counts();
|
|
#endif
|
|
|
|
gc_epilogue(false);
|
|
}
|
|
|
|
// Print the remainder of the GC log output.
|
|
if (evacuation_failed()) {
|
|
log_info(gc)("To-space exhausted");
|
|
}
|
|
|
|
g1_policy()->print_phases();
|
|
heap_transition.print();
|
|
|
|
// It is not yet to safe to tell the concurrent mark to
|
|
// start as we have some optional output below. We don't want the
|
|
// output from the concurrent mark thread interfering with this
|
|
// logging output either.
|
|
|
|
_hrm.verify_optional();
|
|
_verifier->verify_region_sets_optional();
|
|
|
|
TASKQUEUE_STATS_ONLY(print_taskqueue_stats());
|
|
TASKQUEUE_STATS_ONLY(reset_taskqueue_stats());
|
|
|
|
print_heap_after_gc();
|
|
print_heap_regions();
|
|
trace_heap_after_gc(_gc_tracer_stw);
|
|
|
|
// We must call G1MonitoringSupport::update_sizes() in the same scoping level
|
|
// as an active TraceMemoryManagerStats object (i.e. before the destructor for the
|
|
// TraceMemoryManagerStats is called) so that the G1 memory pools are updated
|
|
// before any GC notifications are raised.
|
|
g1mm()->update_sizes();
|
|
|
|
_gc_tracer_stw->report_evacuation_info(&evacuation_info);
|
|
_gc_tracer_stw->report_tenuring_threshold(_g1_policy->tenuring_threshold());
|
|
_gc_timer_stw->register_gc_end();
|
|
_gc_tracer_stw->report_gc_end(_gc_timer_stw->gc_end(), _gc_timer_stw->time_partitions());
|
|
}
|
|
// It should now be safe to tell the concurrent mark thread to start
|
|
// without its logging output interfering with the logging output
|
|
// that came from the pause.
|
|
|
|
if (should_start_conc_mark) {
|
|
// CAUTION: after the doConcurrentMark() call below,
|
|
// the concurrent marking thread(s) could be running
|
|
// concurrently with us. Make sure that anything after
|
|
// this point does not assume that we are the only GC thread
|
|
// running. Note: of course, the actual marking work will
|
|
// not start until the safepoint itself is released in
|
|
// SuspendibleThreadSet::desynchronize().
|
|
do_concurrent_mark();
|
|
}
|
|
|
|
return true;
|
|
}<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></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></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>往下走就是这一步<code>G1Policy::finalize_collection_set</code>,去处理新生代和老年代</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">void G1Policy::finalize_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) {
|
|
double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms, survivor);
|
|
_collection_set->finalize_old_part(time_remaining_ms);
|
|
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre><p>这里分别调用了两个方法，可以看到剩余时间是往下传的，来看一下具体的方法</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
|
|
double young_start_time_sec = os::elapsedTime();
|
|
|
|
finalize_incremental_building();
|
|
|
|
guarantee(target_pause_time_ms > 0.0,
|
|
"target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
|
|
|
|
size_t pending_cards = _policy->pending_cards();
|
|
double base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
|
|
double time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, 0.0);
|
|
|
|
log_trace(gc, ergo, cset)("Start choosing CSet. pending cards: " SIZE_FORMAT " predicted base time: %1.2fms remaining time: %1.2fms target pause time: %1.2fms",
|
|
pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);
|
|
|
|
// The young list is laid with the survivor regions from the previous
|
|
// pause are appended to the RHS of the young list, i.e.
|
|
// [Newly Young Regions ++ Survivors from last pause].
|
|
|
|
uint survivor_region_length = survivors->length();
|
|
uint eden_region_length = _g1h->eden_regions_count();
|
|
init_region_lengths(eden_region_length, survivor_region_length);
|
|
|
|
verify_young_cset_indices();
|
|
|
|
// Clear the fields that point to the survivor list - they are all young now.
|
|
survivors->convert_to_eden();
|
|
|
|
_bytes_used_before = _inc_bytes_used_before;
|
|
time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, 0.0);
|
|
|
|
log_trace(gc, ergo, cset)("Add young regions to CSet. eden: %u regions, survivors: %u regions, predicted young region time: %1.2fms, target pause time: %1.2fms",
|
|
eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);
|
|
|
|
// The number of recorded young regions is the incremental
|
|
// collection set's current size
|
|
set_recorded_rs_lengths(_inc_recorded_rs_lengths);
|
|
|
|
double young_end_time_sec = os::elapsedTime();
|
|
phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * 1000.0);
|
|
|
|
return time_remaining_ms;
|
|
}<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></code></pre><p>下面是老年代的部分</p><pre class="line-numbers language-C++" data-language="C++"><code class="language-C++">void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
|
|
double non_young_start_time_sec = os::elapsedTime();
|
|
double predicted_old_time_ms = 0.0;
|
|
|
|
if (collector_state()->in_mixed_phase()) {
|
|
cset_chooser()->verify();
|
|
const uint min_old_cset_length = _policy->calc_min_old_cset_length();
|
|
const uint max_old_cset_length = _policy->calc_max_old_cset_length();
|
|
|
|
uint expensive_region_num = 0;
|
|
bool check_time_remaining = _policy->adaptive_young_list_length();
|
|
|
|
HeapRegion* hr = cset_chooser()->peek();
|
|
while (hr != NULL) {
|
|
if (old_region_length() >= max_old_cset_length) {
|
|
// Added maximum number of old regions to the CSet.
|
|
log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached max). old %u regions, max %u regions",
|
|
old_region_length(), max_old_cset_length);
|
|
break;
|
|
}
|
|
|
|
// Stop adding regions if the remaining reclaimable space is
|
|
// not above G1HeapWastePercent.
|
|
size_t reclaimable_bytes = cset_chooser()->remaining_reclaimable_bytes();
|
|
double reclaimable_percent = _policy->reclaimable_bytes_percent(reclaimable_bytes);
|
|
double threshold = (double) G1HeapWastePercent;
|
|
if (reclaimable_percent <= threshold) {
|
|
// We've added enough old regions that the amount of uncollected
|
|
// reclaimable space is at or below the waste threshold. Stop
|
|
// adding old regions to the CSet.
|
|
log_debug(gc, ergo, cset)("Finish adding old regions to CSet (reclaimable percentage not over threshold). "
|
|
"old %u regions, max %u regions, reclaimable: " SIZE_FORMAT "B (%1.2f%%) threshold: " UINTX_FORMAT "%%",
|
|
old_region_length(), max_old_cset_length, reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
|
|
break;
|
|
}
|
|
|
|
double predicted_time_ms = predict_region_elapsed_time_ms(hr);
|
|
if (check_time_remaining) {
|
|
if (predicted_time_ms > time_remaining_ms) {
|
|
// Too expensive for the current CSet.
|
|
|
|
if (old_region_length() >= min_old_cset_length) {
|
|
// We have added the minimum number of old regions to the CSet,
|
|
// we are done with this CSet.
|
|
log_debug(gc, ergo, cset)("Finish adding old regions to CSet (predicted time is too high). "
|
|
"predicted time: %1.2fms, remaining time: %1.2fms old %u regions, min %u regions",
|
|
predicted_time_ms, time_remaining_ms, old_region_length(), min_old_cset_length);
|
|
break;
|
|
}
|
|
|
|
// We'll add it anyway given that we haven't reached the
|
|
// minimum number of old regions.
|
|
expensive_region_num += 1;
|
|
}
|
|
} else {
|
|
if (old_region_length() >= min_old_cset_length) {
|
|
// In the non-auto-tuning case, we'll finish adding regions
|
|
// to the CSet if we reach the minimum.
|
|
|
|
log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached min). old %u regions, min %u regions",
|
|
old_region_length(), min_old_cset_length);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// We will add this region to the CSet.
|
|
time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
|
|
predicted_old_time_ms += predicted_time_ms;
|
|
cset_chooser()->pop(); // already have region via peek()
|
|
_g1h->old_set_remove(hr);
|
|
add_old_region(hr);
|
|
|
|
hr = cset_chooser()->peek();
|
|
}
|
|
if (hr == NULL) {
|
|
log_debug(gc, ergo, cset)("Finish adding old regions to CSet (candidate old regions not available)");
|
|
}
|
|
|
|
if (expensive_region_num > 0) {
|
|
// We print the information once here at the end, predicated on
|
|
// whether we added any apparently expensive regions or not, to
|
|
// avoid generating output per region.
|
|
log_debug(gc, ergo, cset)("Added expensive regions to CSet (old CSet region num not reached min)."
|
|
"old: %u regions, expensive: %u regions, min: %u regions, remaining time: %1.2fms",
|
|
old_region_length(), expensive_region_num, min_old_cset_length, time_remaining_ms);
|
|
}
|
|
|
|
cset_chooser()->verify();
|
|
}
|
|
|
|
stop_incremental_building();
|
|
|
|
log_debug(gc, ergo, cset)("Finish choosing CSet. old: %u regions, predicted old region time: %1.2fms, time remaining: %1.2f",
|
|
old_region_length(), predicted_old_time_ms, time_remaining_ms);
|
|
|
|
double non_young_end_time_sec = os::elapsedTime();
|
|
phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
|
|
|
|
QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx, true);
|
|
}<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><p>上面第三行是个判断，当前是否是 mixed 回收阶段，如果不是的话其实是没有老年代什么事的，所以可以看到代码基本是从这个 if 判断<br><code>if (collector_state()->in_mixed_phase()) {</code>开始往下走的<br>先写到这，偏向于做笔记用，有错轻拍</p></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2019/09/23/AbstractQueuedSynchronizer/"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="image" content="/uploads/avatar.jpg"><meta itemprop="name" content="Nicksxs"><meta itemprop="description" content="learn from zero,技术博客，Nicksxs，史学森"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="Nicksxs's Blog"></span><header class="post-header"><h2 class="post-title" itemprop="name headline"><a href="/2019/09/23/AbstractQueuedSynchronizer/" class="post-title-link" itemprop="url">AbstractQueuedSynchronizer</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 title="创建时间：2019-09-23 23:40:05" itemprop="dateCreated datePublished" datetime="2019-09-23T23:40:05+08:00">2019-09-23</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><span id="/2019/09/23/AbstractQueuedSynchronizer/" class="post-meta-item leancloud_visitors" data-flag-title="AbstractQueuedSynchronizer" 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 title="disqus" href="/2019/09/23/AbstractQueuedSynchronizer/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2019/09/23/AbstractQueuedSynchronizer/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>最近看了大神的 AQS 的文章，之前总是断断续续地看一点，每次都知难而退，下次看又从头开始，昨天总算硬着头皮看完了第一部分<br>首先 AQS 只要有这些属性</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">// 头结点，你直接把它当做 当前持有锁的线程 可能是最好理解的</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">transient</span> <span class="token keyword">volatile</span> <span class="token class-name">Node</span> head<span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">// 阻塞的尾节点，每个新的节点进来，都插入到最后，也就形成了一个链表</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">transient</span> <span class="token keyword">volatile</span> <span class="token class-name">Node</span> tail<span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">// 这个是最重要的，代表当前锁的状态，0代表没有被占用，大于 0 代表有线程持有当前锁</span>
|
|
<span class="token comment">// 这个值可以大于 1，是因为锁可以重入，每次重入都加上 1</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">volatile</span> <span class="token keyword">int</span> state<span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">// 代表当前持有独占锁的线程，举个最重要的使用例子，因为锁可以重入</span>
|
|
<span class="token comment">// reentrantLock.lock()可以嵌套调用多次，所以每次用这个来判断当前线程是否已经拥有了锁</span>
|
|
<span class="token comment">// if (currentThread == getExclusiveOwnerThread()) {state++}</span>
|
|
<span class="token keyword">private</span> <span class="token keyword">transient</span> <span class="token class-name">Thread</span> exclusiveOwnerThread<span class="token punctuation">;</span> <span class="token comment">//继承自AbstractOwnableSynchronizer</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></code></pre><p>大概了解了 aqs 底层的双向等待队列，<br>结构是这样的<br><img data-src="https://tva1.sinaimg.cn/large/006tNbRwly1g9mxu0ndt1j319o08w0t7.jpg"><br>每个 node 里面主要是的代码结构也比较简单</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">Node</span> <span class="token punctuation">{</span>
|
|
<span class="token comment">// 标识节点当前在共享模式下</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">Node</span> SHARED <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 punctuation">)</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// 标识节点当前在独占模式下</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">Node</span> EXCLUSIVE <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
|
|
|
|
<span class="token comment">// ======== 下面的几个int常量是给waitStatus用的 ===========</span>
|
|
<span class="token comment">/** waitStatus value to indicate thread has cancelled */</span>
|
|
<span class="token comment">// 代码此线程取消了争抢这个锁</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> CANCELLED <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
|
|
<span class="token comment">/** waitStatus value to indicate successor's thread needs unparking */</span>
|
|
<span class="token comment">// 官方的描述是，其表示当前node的后继节点对应的线程需要被唤醒</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> SIGNAL <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
|
|
<span class="token comment">/** waitStatus value to indicate thread is waiting on condition */</span>
|
|
<span class="token comment">// 本文不分析condition，所以略过吧，下一篇文章会介绍这个</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> CONDITION <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">;</span>
|
|
<span class="token comment">/**
|
|
* waitStatus value to indicate the next acquireShared should
|
|
* unconditionally propagate
|
|
*/</span>
|
|
<span class="token comment">// 同样的不分析，略过吧</span>
|
|
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> PROPAGATE <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">3</span><span class="token punctuation">;</span>
|
|
<span class="token comment">// =====================================================</span>
|
|
|
|
|
|
<span class="token comment">// 取值为上面的1、-1、-2、-3，或者0(以后会讲到)</span>
|
|
<span class="token comment">// 这么理解，暂时只需要知道如果这个值 大于0 代表此线程取消了等待，</span>
|
|
<span class="token comment">// ps: 半天抢不到锁，不抢了，ReentrantLock是可以指定timeouot的。。。</span>
|
|
<span class="token keyword">volatile</span> <span class="token keyword">int</span> waitStatus<span class="token punctuation">;</span>
|
|
<span class="token comment">// 前驱节点的引用</span>
|
|
<span class="token keyword">volatile</span> <span class="token class-name">Node</span> prev<span class="token punctuation">;</span>
|
|
<span class="token comment">// 后继节点的引用</span>
|
|
<span class="token keyword">volatile</span> <span class="token class-name">Node</span> next<span class="token punctuation">;</span>
|
|
<span class="token comment">// 这个就是线程本尊</span>
|
|
<span class="token keyword">volatile</span> <span class="token class-name">Thread</span> thread<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></code></pre><p>其实可以主要关注这个 <code>waitStatus</code> 因为这个是后面的节点给前面的节点设置的，等于-1 的时候代表后面有节点等待，需要去唤醒，<br>这里使用了一个变种的 CLH 队列实现，CLH 队列相关内容可以查看这篇 <a target="_blank" rel="noopener" href="https://coderbee.net/index.php/concurrent/20131115/577">自旋锁、排队自旋锁、MCS锁、CLH锁</a></p></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2019/06/18/openresty/"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="image" content="/uploads/avatar.jpg"><meta itemprop="name" content="Nicksxs"><meta itemprop="description" content="learn from zero,技术博客，Nicksxs，史学森"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="Nicksxs's Blog"></span><header class="post-header"><h2 class="post-title" itemprop="name headline"><a href="/2019/06/18/openresty/" class="post-title-link" itemprop="url">openresty</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 title="创建时间：2019-06-18 19:03:05" itemprop="dateCreated datePublished" datetime="2019-06-18T19:03:05+08:00">2019-06-18</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/nginx/" itemprop="url" rel="index"><span itemprop="name">nginx</span></a> </span></span><span id="/2019/06/18/openresty/" class="post-meta-item leancloud_visitors" data-flag-title="openresty" 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 title="disqus" href="/2019/06/18/openresty/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2019/06/18/openresty/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><p>目前公司要对一些新的产品功能做灰度测试，因为在后端业务代码层面添加判断比较麻烦，所以想在nginx上做点手脚，就想到了openresty<br>前后也踩了不少坑，这边先写一点</p><p>首先是日志<br><code>error_log logs/error.log debug;</code><br>需要nginx开启日志的debug才能看到日志</p><p>使用 <code>lua_code_cache off</code>即可, 另外注意只有使用 <code>content_by_lua_file</code> 才会生效</p><pre class="line-numbers language-lua" data-language="lua"><code class="language-lua"><span class="token function">http</span> <span class="token punctuation">{</span>
|
|
lua_code_cache off<span class="token punctuation">;</span>
|
|
<span class="token punctuation">}</span>
|
|
|
|
location <span class="token operator">~</span><span class="token operator">*</span> <span class="token operator">/</span><span class="token punctuation">(</span>\d<span class="token operator">+</span><span class="token operator">-</span><span class="token punctuation">.</span><span class="token operator">*</span><span class="token punctuation">)</span><span class="token operator">/</span>api<span class="token operator">/</span>orgunits<span class="token operator">/</span><span class="token function">load_all</span><span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token operator">*</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
default_type <span class="token string">'application/json;charset=utf-8'</span><span class="token punctuation">;</span>
|
|
content_by_lua_file <span class="token operator">/</span>data<span class="token operator">/</span>projects<span class="token operator">/</span>xxx<span class="token operator">/</span>current<span class="token operator">/</span>lua<span class="token operator">/</span>controller<span class="token operator">/</span>load_data<span class="token punctuation">.</span>lua<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></code></pre><p>使用lua给nginx请求response头添加内容可以用这个</p><pre class="line-numbers language-lua" data-language="lua"><code class="language-lua">ngx<span class="token punctuation">.</span>header<span class="token punctuation">[</span><span class="token string">'response'</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">'header'</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><p><a target="_blank" rel="noopener" href="http://cyukang.com/2017/05/22/try-on-openresty.html">使用总结</a></p><p>后续：</p><ol><li>一开始在本地环境的时候使用content_by_lua_file只关注了头，后来发到测试环境发现请求内容都没代理转发到后端服务上<br>网上查了下发现content_by_lua_file是将请求的所有内容包括response都用这里面的lua脚本生成了，content这个词就表示是请求内容<br>后来改成了access_by_lua_file就正常了，只是要去获取请求内容和修改响应头，并不是要完整的接管请求</li></ol><ol start="2"><li><p>后来又碰到了一个坑是nginx有个client_body_buffer_size的配置参数，nginx在32位和64位系统里有8K和16K两个默认值，当请求内容大于这两个值的时候，会把请求内容放到临时文件里，这个时候openresty里的ngx.req.get_post_args()就会报“failed to get post args: requesty body in temp file not supported”这个错误，将client_body_buffer_size这个参数配置调大一点就好了</p></li><li><p>还有就是lua的异常捕获，网上看一般是用pcall和xpcall来进行保护调用，因为问题主要出在cjson的decode，这里有两个解决方案，一个就是将cjson.decode使用pcall封装，</p><pre class="line-numbers language-lua" data-language="lua"><code class="language-lua"><span class="token keyword">local</span> decode <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">"cjson"</span><span class="token punctuation">)</span><span class="token punctuation">.</span>decode
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<span class="token keyword">function</span> <span class="token function">json_decode</span><span class="token punctuation">(</span> str <span class="token punctuation">)</span>
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<span class="token keyword">local</span> ok<span class="token punctuation">,</span> t <span class="token operator">=</span> <span class="token function">pcall</span><span class="token punctuation">(</span>decode<span class="token punctuation">,</span> str<span class="token punctuation">)</span>
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<span class="token keyword">if</span> <span class="token keyword">not</span> ok <span class="token keyword">then</span>
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<span class="token keyword">return</span> <span class="token keyword">nil</span>
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<span class="token keyword">end</span>
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<span class="token keyword">return</span> t
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<span class="token keyword">end</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></code></pre><p>这个是使用了pcall，称为保护调用，会在内部错误后返回两个参数，第一个是false，第二个是错误信息<br>还有一种是使用cjson.safe包</p><pre class="line-numbers language-lua" data-language="lua"><code class="language-lua"><span class="token keyword">local</span> json <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">"cjson.safe"</span><span class="token punctuation">)</span>
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<span class="token keyword">local</span> str <span class="token operator">=</span> <span class="token string">[[ {"key:"value"} ]]</span>
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<span class="token keyword">local</span> t <span class="token operator">=</span> json<span class="token punctuation">.</span><span class="token function">decode</span><span class="token punctuation">(</span>str<span class="token punctuation">)</span>
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<span class="token keyword">if</span> t <span class="token keyword">then</span>
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ngx<span class="token punctuation">.</span><span class="token function">say</span><span class="token punctuation">(</span><span class="token string">" --> "</span><span class="token punctuation">,</span> <span class="token function">type</span><span class="token punctuation">(</span>t<span class="token punctuation">)</span><span class="token punctuation">)</span>
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<span class="token keyword">end</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>cjson.safe包会在解析失败的时候返回nil</p></li><li><p>还有一个是redis链接时如果host使用的是域名的话会提示“failed to connect: no resolver defined to resolve “redis.xxxxxx.com””，这里需要使用nginx的resolver指令，<br><code>resolver 8.8.8.8 valid=3600s;</code></p></li><li><p>还有一点补充下<br>就是业务在使用redis的时候使用了db的特性，所以在lua访问redis的时候也需要执行db，这里lua的redis库也支持了这个特性，可以使用instance:select(config:get(‘db’))来切换db</p></li><li><p>性能优化tips<br><a target="_blank" rel="noopener" href="https://juejin.im/entry/5b0e8fcef265da09210072a3#openresty">建议是尽量少使用阶段钩子，例如content_by_lua_file，*_by_lua</a></p></li><li><p>发现一个不错的openresty站点<br><a target="_blank" rel="noopener" href="http://orhub.org/">地址</a></p></li></ol></div><footer class="post-footer"><div class="post-eof"></div></footer></article></div><div class="post-block"><article itemscope itemtype="http://schema.org/Article" class="post-content"><link itemprop="mainEntityOfPage" href="https://nicksxs.me/2017/05/09/ambari-summary/"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="image" content="/uploads/avatar.jpg"><meta itemprop="name" content="Nicksxs"><meta itemprop="description" content="learn from zero,技术博客，Nicksxs，史学森"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="Nicksxs's Blog"></span><header class="post-header"><h2 class="post-title" itemprop="name headline"><a href="/2017/05/09/ambari-summary/" class="post-title-link" itemprop="url">ambari-summary</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 title="创建时间：2017-05-09 23:53:05" itemprop="dateCreated datePublished" datetime="2017-05-09T23:53:05+08:00">2017-05-09</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/data-analysis/" itemprop="url" rel="index"><span itemprop="name">data analysis</span></a> </span></span><span id="/2017/05/09/ambari-summary/" class="post-meta-item leancloud_visitors" data-flag-title="ambari-summary" 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 title="disqus" href="/2017/05/09/ambari-summary/#disqus_thread" itemprop="discussionUrl"><span class="post-comments-count disqus-comment-count" data-disqus-identifier="2017/05/09/ambari-summary/" itemprop="commentCount"></span></a></span></div></div></header><div class="post-body" itemprop="articleBody"><h2 id="初识ambari"><a href="#初识ambari" class="headerlink" title="初识ambari"></a>初识ambari</h2><p><a target="_blank" rel="noopener" href="http://ambari.apache.org/">ambari</a>是一个大数据平台的管理工具，包含了<code>hadoop</code>, <code>yarn</code>, <code>hive</code>, <code>hbase</code>, <code>spark</code>等大数据的基础架构和工具，简化了数据平台的搭建，之前只是在同事搭建好平台后的一些使用，这次有机会从头开始用<code>ambari</code>来搭建一个测试的数据平台，过程中也踩到不少坑，简单记录下。</p><h2 id="简单过程"><a href="#简单过程" class="headerlink" title="简单过程"></a>简单过程</h2><ul><li>第一个坑<br>在刚开始是按照官网的指南，用maven构建，因为GFW的原因，导致反复失败等待，也就是这个<a target="_blank" rel="noopener" href="https://cwiki.apache.org/confluence/display/AMBARI/Installation+Guide+for+Ambari+2.5.0">guide</a>，因为对maven不熟悉导致有些按图索骥，浪费了很多时间，之后才知道可以直接加repo用yum安装，然而用yum安装马上就出现了第二个坑。</li><li>第二个坑<br>因为在线的repo还是因为网络原因很慢很慢，用proxychains勉强把ambari-server本身安装好了，<a target="_blank" rel="noopener" href="http://public-repo-1.hortonworks.com/ambari/centos7/2.x/updates/2.5.0.3/ambari.repo">ambari.repo</a>将这个放进<code>/etc/yum.repos.d/</code>路径下，然后<code>yum update && yum install ambari-server</code>安装即可，如果有条件就用proxychains走下代理。</li><li>第三步<br>安装好ambari-server后先执行<code>ambari-server setup</code>做一些初始化设置，其中包含了JDK路径的设置，数据库设置，设置好就OK了，然后执行<code>ambari-server start</code>启动服务，这里有个小插曲，因为<code>ambari-server</code>涉及到这么多服务，所以管理控制监控之类的模块是必不可少的，这部分可以在<code>ambari-server</code>的web ui界面安装，也可以命令行提前安装，这部分被称为<code>HDF Management Pack</code>，运行```ambari-server install-mpack \</li><li>-mpack=<a target="_blank" rel="noopener" href="http://public-repo-1.hortonworks.com/HDF/centos7/2.x/updates/2.1.4.0/tars/hdf_ambari_mp/hdf-ambari-mpack-2.1.4.0-5.tar.gz">http://public-repo-1.hortonworks.com/HDF/centos7/2.x/updates/2.1.4.0/tars/hdf_ambari_mp/hdf-ambari-mpack-2.1.4.0-5.tar.gz</a> \</li><li>-purge \</li><li>-verbose```<br>安装，当然这个压缩包可以下载之后指到本地路径安装，然后就可以重启<code>ambari-server</code></li></ul></div><footer 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