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<a href="/2021/03/14/Leetcode-121-%E4%B9%B0%E5%8D%96%E8%82%A1%E7%A5%A8%E7%9A%84%E6%9C%80%E4%BD%B3%E6%97%B6%E6%9C%BA-Best-Time-to-Buy-and-Sell-Stock-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/" class="post-title-link" itemprop="url">Leetcode 121 买卖股票的最佳时机(Best Time to Buy and Sell Stock) 题解分析</a>
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<time title="Created: 2021-03-14 22:34:30" itemprop="dateCreated datePublished" datetime="2021-03-14T22:34:30+08:00">2021-03-14</time>
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,
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,
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,
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,
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<span id="/2021/03/14/Leetcode-121-%E4%B9%B0%E5%8D%96%E8%82%A1%E7%A5%A8%E7%9A%84%E6%9C%80%E4%BD%B3%E6%97%B6%E6%9C%BA-Best-Time-to-Buy-and-Sell-Stock-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/" class="post-meta-item leancloud_visitors" data-flag-title="Leetcode 121 买卖股票的最佳时机(Best Time to Buy and Sell Stock) 题解分析" title="Views">
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<a title="disqus" href="/2021/03/14/Leetcode-121-%E4%B9%B0%E5%8D%96%E8%82%A1%E7%A5%A8%E7%9A%84%E6%9C%80%E4%BD%B3%E6%97%B6%E6%9C%BA-Best-Time-to-Buy-and-Sell-Stock-%E9%A2%98%E8%A7%A3%E5%88%86%E6%9E%90/#disqus_thread" itemprop="discussionUrl">
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<span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/03/14/Leetcode-121-买卖股票的最佳时机-Best-Time-to-Buy-and-Sell-Stock-题解分析/" itemprop="commentCount"></span>
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<h3 id="题目介绍"><a href="#题目介绍" class="headerlink" title="题目介绍"></a>题目介绍</h3><p>You are given an array <code>prices</code> where <code>prices[i]</code> is the price of a given stock on the i<sup>th</sup> day.</p>
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<p>You want to maximize your profit by choosing a <strong>single day</strong> to buy one stock and choosing a <strong>different day in the future</strong> to sell that stock.</p>
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<p>Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return <code>0</code>.</p>
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<p>给定一个数组 <code>prices</code> ，它的第 <code>i</code> 个元素 <code>prices[i]</code> 表示一支给定股票第 <code>i</code> 天的价格。</p>
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<p>你只能选择 <strong>某一天</strong> 买入这只股票，并选择在 <strong>未来的某一个不同的日子</strong> 卖出该股票。设计一个算法来计算你所能获取的最大利润。</p>
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<p>返回你可以从这笔交易中获取的最大利润。如果你不能获取任何利润，返回 <code>0</code> 。</p>
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<h3 id="简单分析"><a href="#简单分析" class="headerlink" title="简单分析"></a>简单分析</h3><p>其实这个跟二叉树的最长路径和有点类似，需要找到整体的最大收益，但是在迭代过程中需要一个当前的值</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="keyword">int</span> maxSofar = <span class="number">0</span>;</span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">maxProfit</span><span class="params">(<span class="keyword">int</span>[] prices)</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (prices.length <= <span class="number">1</span>) {</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">int</span> maxIn = prices[<span class="number">0</span>];</span><br><span class="line"> <span class="keyword">int</span> maxOut = prices[<span class="number">0</span>];</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">1</span>; i < prices.length; i++) {</span><br><span class="line"> <span class="keyword">if</span> (maxIn > prices[i]) {</span><br><span class="line"> <span class="comment">// 当循环当前值小于之前的买入值时就当成买入值，同时卖出也要更新</span></span><br><span class="line"> maxIn = prices[i];</span><br><span class="line"> maxOut = prices[i];</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> (prices[i] > maxOut) {</span><br><span class="line"> <span class="comment">// 表示一个可卖出点，即比买入值高时</span></span><br><span class="line"> maxOut = prices[i];</span><br><span class="line"> <span class="comment">// 需要设置一个历史值</span></span><br><span class="line"> maxSofar = Math.max(maxSofar, maxOut - maxIn);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> maxSofar;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<h3 id="总结下"><a href="#总结下" class="headerlink" title="总结下"></a>总结下</h3><p>一开始看到 easy 就觉得是很简单，就没有 maxSofar ，但是一提交就出现问题了<br>对于<code>[2, 4, 1]</code>这种就会变成 0，所以还是需要一个历史值来存放历史最大值，这题有点动态规划的意思</p>
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<a href="/2021/03/07/%E3%80%8A%E5%9E%83%E5%9C%BE%E5%9B%9E%E6%94%B6%E7%AE%97%E6%B3%95%E6%89%8B%E5%86%8C%E8%AF%BB%E4%B9%A6%E3%80%8B%E7%AC%94%E8%AE%B0%E4%B9%8B%E6%95%B4%E7%90%86%E7%AE%97%E6%B3%95/" class="post-title-link" itemprop="url">《垃圾回收算法手册读书》笔记之整理算法</a>
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<p>最近看了下这本垃圾回收算法手册，看到了第三章的标记-整理回收算法，做个简单的读书笔记</p>
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<h3 id="双指针整理算法"><a href="#双指针整理算法" class="headerlink" title="双指针整理算法"></a>双指针整理算法</h3><p>对于一块待整理区域，通过两个指针，free 在区域的起始端，scan 指针在区域的末端，free 指针从前往后知道找到空闲区域，scan 从后往前一直找到存活对象，当 free 指针未与 scan 指针交叉时，会给 scan 位置的对象特定位置标记上 free 的地址，即将要转移的地址，不过这里有个限制，这种整理算法一般会用于对象大小统一的情况，否则 free 指针扫描时还需要匹配scan 指针扫描到的存活对象的大小。<br><img data-src="https://gitee.com/nicksxs/images/raw/master/uPic/yLQlgj.png" alt=""></p>
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<h3 id="Lisp-2-整理算法"><a href="#Lisp-2-整理算法" class="headerlink" title="Lisp 2 整理算法"></a>Lisp 2 整理算法</h3><p>需要三次完整遍历堆区域<br>第一遍是遍历后将计算出所有对象的最终地址（转发地址）<br>第二遍是使用转发地址更新赋值器线程根以及被标记对象中的引用，该操作将确保它们指向对象的新位置<br>第三次遍历是relocate最终将存活对象移动到其新的目标位置</p>
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<h3 id="引线整理算法"><a href="#引线整理算法" class="headerlink" title="引线整理算法"></a>引线整理算法</h3><p>这个真的长见识了，<br><img data-src="https://gitee.com/nicksxs/images/raw/master/uPic/6yeA7n.png" alt=""><br>可以看到，原来是 A，B，C 对象引用了 N，这里会在第一次遍历的时候把这种引用反过来，让 N 的对象头部保存下 A 的地址，表示这类引用，然后在遍历到 B 的时候在链起来，到最后就会把所有引用了 N 对象的所有对象通过引线链起来，在第二次遍历的时候就把更新A，B，C 对象引用的 N 地址，并且移动 N 对象</p>
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<h3 id="单次遍历算法"><a href="#单次遍历算法" class="headerlink" title="单次遍历算法"></a>单次遍历算法</h3><p>这个一直提到过位图的实现方式，<br><img data-src="https://gitee.com/nicksxs/images/raw/master/uPic/Jqtuzu.png" alt=""><br>可以看到在第一步会先通过位图标记，标记的方式是位图的每一位对应的堆内存的一个字（这里可能指的是 byte 吧），然后将一个存活对象的内存区域的第一个字跟最后一个字标记，这里如果在通过普通的方式就还需要一个地方在存转发地址，但是因为具体的位置可以通过位图算出来，也就不需要额外记录了</p>
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<p>新年开工开车来杭州，因为没有车位加限行今天来就没开车来了，从东站做公交回住的地方，这班神奇的车我之前也吐槽过了，有神奇的乘客和神奇的司机，因为基本上这班车是从我毕业就开始乘了，所以也算是比较熟悉了，以前总体感觉不太好的是乘坐时间太长了，不过这个也不能怪车，是我自己住得远（离东站），后来住到了现在的地方，也算是直达，并且 LD 比较喜欢直达的，不爱更快却要换乘的地铁，所以坐的频率比较高，也说过前面那些比较气人的乘客，自己不好好戴口罩，反而联合一起上车的乘客诽谤司机，说他要吃人了要打人了，也正是这个司机比较有意思，上车就让戴好口罩，还给大家讲，哪里哪里又有疫情了，我觉得其实这个司机还是不错的，特殊时期，对于这种公共交通，这样的确是比较负责任的做法，只是说话方式，语气这个因人而异，他也不是来伺候人的，而且这么一大车人，说了一遍不行，再说一遍，三遍以上了，嗓门大一点也属于正常的人的行为。<br>还是说回今天要说的，今天这位司机我看着跟前面说的那位有点像，因为上车的时候比较暗没看清脸，主要原因是这位司机开车比较猛，比较急，然后车上因为这个时间点，比较多大学开学来的学生，拎着个行李箱，一开始是前面已经都站满了人，后面还有很多空位，因为后面没地方放行李箱，就因为这样前面站着的有几个就在说司机开慢点，结果司机貌似也没听进去，还是我行我素，过了会又有人说司机开稳一点，就在这个人说完没一会，停在红绿灯路口的车里，就有人问有没有垃圾桶，接着又让司机开门，说晕车太严重了，要下车，司机开了门，我望出去两个妹子下了车，好像在路边草丛吐了，前面开门下车的时候就有人说她们第一次来杭州，可能有点责怪司机开的不稳，也影响了杭州交通给新来杭州的人的感受，说完了事情经过，其实我有蛮多感触，对于杭州公交司机，我大概是大一来了没多久，陪室友去文三路买电脑就晕车，下车的时候在公交车站吐了，可能是从大学开始缺乏锻炼，又饮食不规律，更加容易晕车，大部分晕车我觉得都是我自己的原因，有时候是上车前吃太多了，或者早上起太早，没睡好，没吃东西，反正自己也是挺多原因的，说到司机的原因的话，我觉得可能这班车还算好的，最让我难受的还是上下班高峰的时候，因为经过的那条路是比较重要的主干道，路比较老比较窄，并且还有很多人行道，所以经常一脚油门连带着一脚刹车，真的很难受，这种算是我觉得真的是公交体验比较差的一点，但是这一点呢也不能完全怪公交司机，杭州的路政规划是很垃圾，没看错，是垃圾，所以总体结论是公交还行，主要是路政规划就是垃圾，包括这条主干道这么多人行道，并且两边都是老小区，老年人在上班高峰可能要买菜送娃或者其他事情，在通畅的情况下可能只需要六分钟的路程，有时候因为各种原因，半小时都开不完，扯开去一点，杭州的路，核心的高速说封就封，本来是高架可以直接通到城西，结果没造，到了路本已经很拥挤的时候开始来造隧道，各种破坏，隧道接高架的地方，无尽的加塞，对于我这样的小白司机来说真的是太恶心了，所以我一直想说的就是杭州这个地方房价领先基础设施十年，地铁，高架，高速通通不行，地面道路就更不行了。<br>总结下，其实杭州的真正的公交体验差，应该还是路造成的，对于前面的那两位妹子来说，有可能是她们来自于公交司机都是开的特别稳，并且路况也很好的地方，也或者是我被虐习惯了🤦♂️</p>
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<p>Condition也是 AQS 中很重要的一块内容，可以先看段示例代码，这段代码应该来自于Doug Lea大大，可以在 javadoc 中的 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Condition.html" target="_blank" rel="noopener">condition</a> 部分找到，其实大大原来写过基于 <code>synchronized</code> 实现的，后面我也贴下代码</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.concurrent.locks.Condition;</span><br><span class="line"><span class="keyword">import</span> java.util.concurrent.locks.Lock;</span><br><span class="line"><span class="keyword">import</span> java.util.concurrent.locks.ReentrantLock;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">BoundedBuffer</span> </span>{</span><br><span class="line"> <span class="keyword">final</span> Lock lock = <span class="keyword">new</span> ReentrantLock();</span><br><span class="line"> <span class="comment">// condition 依赖于 lock 来产生</span></span><br><span class="line"> <span class="keyword">final</span> Condition notFull = lock.newCondition();</span><br><span class="line"> <span class="keyword">final</span> Condition notEmpty = lock.newCondition();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 对象池子，put 跟 take 的就是这里的</span></span><br><span class="line"> <span class="keyword">final</span> Object[] items = <span class="keyword">new</span> Object[<span class="number">100</span>];</span><br><span class="line"> <span class="keyword">int</span> putptr, takeptr, count;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 生产</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">put</span><span class="params">(Object x)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> <span class="comment">// 这里也说明了，需要先拥有锁</span></span><br><span class="line"> lock.lock();</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">while</span> (count == items.length)</span><br><span class="line"> notFull.await(); <span class="comment">// 队列已满，等待，直到 not full 才能继续生产</span></span><br><span class="line"> items[putptr] = x;</span><br><span class="line"> <span class="keyword">if</span> (++putptr == items.length) putptr = <span class="number">0</span>;</span><br><span class="line"> ++count;</span><br><span class="line"> notEmpty.signal(); <span class="comment">// 生产成功，队列已经 not empty 了，发个通知出去</span></span><br><span class="line"> } <span class="keyword">finally</span> {</span><br><span class="line"> lock.unlock();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 消费</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> Object <span class="title">take</span><span class="params">()</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> lock.lock();</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">while</span> (count == <span class="number">0</span>)</span><br><span class="line"> notEmpty.await(); <span class="comment">// 队列为空，等待，直到队列 not empty，才能继续消费</span></span><br><span class="line"> Object x = items[takeptr];</span><br><span class="line"> <span class="keyword">if</span> (++takeptr == items.length) takeptr = <span class="number">0</span>;</span><br><span class="line"> --count;</span><br><span class="line"> notFull.signal(); <span class="comment">// 被我消费掉一个，队列 not full 了，发个通知出去</span></span><br><span class="line"> <span class="keyword">return</span> x;</span><br><span class="line"> } <span class="keyword">finally</span> {</span><br><span class="line"> lock.unlock();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>介绍下 Condition 的结构</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ConditionObject</span> <span class="keyword">implements</span> <span class="title">Condition</span>, <span class="title">java</span>.<span class="title">io</span>.<span class="title">Serializable</span> </span>{</span><br><span class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> serialVersionUID = <span class="number">1173984872572414699L</span>;</span><br><span class="line"> <span class="comment">/** First node of condition queue. */</span></span><br><span class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> Node firstWaiter;</span><br><span class="line"> <span class="comment">/** Last node of condition queue. */</span></span><br><span class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> Node lastWaiter;</span><br></pre></td></tr></table></figure>
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<p>主要的就这么点，而且也复用了 AQS 阻塞队列或者大大叫 <code>lock queue</code>中同样的 Node 节点，只不过它没有使用其中的双向队列，也就是prev 和 next，而是在 Node 中的 nextWaiter，所以只是个单向的队列，没使用 next 其实还有个用处，后面会提到，看下结构的示意图<br><img data-src="https://gitee.com/nicksxs/images/raw/master/uPic/Ss9oFX.png" alt=""><br>然后主要是看两个方法，<code>await</code> 和 <code>signal</code>,<br>先来看下 await</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Implements interruptible condition wait.</span></span><br><span class="line"><span class="comment"> * <ol></span></span><br><span class="line"><span class="comment"> * <li> If current thread is interrupted, throw InterruptedException.</span></span><br><span class="line"><span class="comment"> * <li> Save lock state returned by {<span class="doctag">@link</span> #getState}.</span></span><br><span class="line"><span class="comment"> * <li> Invoke {<span class="doctag">@link</span> #release} with saved state as argument,</span></span><br><span class="line"><span class="comment"> * throwing IllegalMonitorStateException if it fails.</span></span><br><span class="line"><span class="comment"> * <li> Block until signalled or interrupted.</span></span><br><span class="line"><span class="comment"> * <li> Reacquire by invoking specialized version of</span></span><br><span class="line"><span class="comment"> * {<span class="doctag">@link</span> #acquire} with saved state as argument.</span></span><br><span class="line"><span class="comment"> * <li> If interrupted while blocked in step 4, throw InterruptedException.</span></span><br><span class="line"><span class="comment"> * </ol></span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">await</span><span class="params">()</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> <span class="keyword">if</span> (Thread.interrupted())</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> InterruptedException();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 将当前节点包装成一个 condition waiter node 节点</span></span><br><span class="line"> Node node = addConditionWaiter();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 完全释放占有的锁，这里需要是占有锁的线程</span></span><br><span class="line"> <span class="keyword">int</span> savedState = fullyRelease(node);</span><br><span class="line"> <span class="keyword">int</span> interruptMode = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 判断下是否在阻塞队列中，因为有可能被其他节点从等待队列移动到阻塞队列</span></span><br><span class="line"> <span class="keyword">while</span> (!isOnSyncQueue(node)) {</span><br><span class="line"> <span class="comment">// park等待，等待被唤醒</span></span><br><span class="line"> LockSupport.park(<span class="keyword">this</span>);</span><br><span class="line"> <span class="keyword">if</span> ((interruptMode = checkInterruptWhileWaiting(node)) != <span class="number">0</span>)</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 被唤醒后进入阻塞队列，等待获取锁，这里继续用了fullyRelease返回的 state</span></span><br><span class="line"> <span class="keyword">if</span> (acquireQueued(node, savedState) && interruptMode != THROW_IE)</span><br><span class="line"> interruptMode = REINTERRUPT;</span><br><span class="line"> <span class="keyword">if</span> (node.nextWaiter != <span class="keyword">null</span>) <span class="comment">// clean up if cancelled</span></span><br><span class="line"> unlinkCancelledWaiters();</span><br><span class="line"> <span class="keyword">if</span> (interruptMode != <span class="number">0</span>)</span><br><span class="line"> reportInterruptAfterWait(interruptMode);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p> 添加条件队列节点</p>
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<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="comment">/**</span></span><br><span class="line"><span class="comment"> * Adds a new waiter to wait queue.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> its new wait node</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">private</span> Node <span class="title">addConditionWaiter</span><span class="params">()</span> </span>{</span><br><span class="line"> Node t = lastWaiter;</span><br><span class="line"> <span class="comment">// If lastWaiter is cancelled, clean out.</span></span><br><span class="line"> <span class="comment">// 如果节点已经不是 CONDITION 状态了，表示已经取消了</span></span><br><span class="line"> <span class="keyword">if</span> (t != <span class="keyword">null</span> && t.waitStatus != Node.CONDITION) {</span><br><span class="line"> <span class="comment">// 把等待队列中取消的节点清理出去</span></span><br><span class="line"> unlinkCancelledWaiters();</span><br><span class="line"> t = lastWaiter;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 把当前线程包装成waitStatus=CONDITION 的节点</span></span><br><span class="line"> Node node = <span class="keyword">new</span> Node(Thread.currentThread(), Node.CONDITION);</span><br><span class="line"> <span class="comment">// 没有 lastWaiter 节点，直接是 firstWaiter</span></span><br><span class="line"> <span class="keyword">if</span> (t == <span class="keyword">null</span>)</span><br><span class="line"> firstWaiter = node;</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="comment">// 不然就接在 lastWaiter 后面</span></span><br><span class="line"> t.nextWaiter = node;</span><br><span class="line"> <span class="comment">// 当前节点就会变成新的 lastWaiter</span></span><br><span class="line"> lastWaiter = node;</span><br><span class="line"> <span class="keyword">return</span> node;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>清理取消的节点</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Unlinks cancelled waiter nodes from condition queue.</span></span><br><span class="line"><span class="comment"> * Called only while holding lock. This is called when</span></span><br><span class="line"><span class="comment"> * cancellation occurred during condition wait, and upon</span></span><br><span class="line"><span class="comment"> * insertion of a new waiter when lastWaiter is seen to have</span></span><br><span class="line"><span class="comment"> * been cancelled. This method is needed to avoid garbage</span></span><br><span class="line"><span class="comment"> * retention in the absence of signals. So even though it may</span></span><br><span class="line"><span class="comment"> * require a full traversal, it comes into play only when</span></span><br><span class="line"><span class="comment"> * timeouts or cancellations occur in the absence of</span></span><br><span class="line"><span class="comment"> * signals. It traverses all nodes rather than stopping at a</span></span><br><span class="line"><span class="comment"> * particular target to unlink all pointers to garbage nodes</span></span><br><span class="line"><span class="comment"> * without requiring many re-traversals during cancellation</span></span><br><span class="line"><span class="comment"> * storms.</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">void</span> <span class="title">unlinkCancelledWaiters</span><span class="params">()</span> </span>{</span><br><span class="line"> Node t = firstWaiter;</span><br><span class="line"> Node trail = <span class="keyword">null</span>;</span><br><span class="line"> <span class="comment">// 循环遍历单向链表的节点，如果状态不是 CONDITION 就清出去</span></span><br><span class="line"> <span class="keyword">while</span> (t != <span class="keyword">null</span>) {</span><br><span class="line"> Node next = t.nextWaiter;</span><br><span class="line"> <span class="comment">// 循环链表操作，清掉取消的节点</span></span><br><span class="line"> <span class="keyword">if</span> (t.waitStatus != Node.CONDITION) {</span><br><span class="line"> t.nextWaiter = <span class="keyword">null</span>;</span><br><span class="line"> <span class="keyword">if</span> (trail == <span class="keyword">null</span>)</span><br><span class="line"> firstWaiter = next;</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> trail.nextWaiter = next;</span><br><span class="line"> <span class="keyword">if</span> (next == <span class="keyword">null</span>)</span><br><span class="line"> lastWaiter = trail;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> trail = t;</span><br><span class="line"> t = next;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>完全释放锁</p>
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<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="comment">/**</span></span><br><span class="line"><span class="comment"> * Invokes release with current state value; returns saved state.</span></span><br><span class="line"><span class="comment"> * Cancels node and throws exception on failure.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> node the condition node for this wait</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> previous sync state</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">final</span> <span class="keyword">int</span> <span class="title">fullyRelease</span><span class="params">(Node node)</span> </span>{</span><br><span class="line"> <span class="keyword">boolean</span> failed = <span class="keyword">true</span>;</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="comment">// 获取下当前的 state 值，因为是可重入的，所以这个值要保存下来</span></span><br><span class="line"> <span class="keyword">int</span> savedState = getState();</span><br><span class="line"> <span class="comment">// 这里还包含比较多操作，不过跟前面分析 AQS 的释放比较类似，不深入了</span></span><br><span class="line"> <span class="keyword">if</span> (release(savedState)) {</span><br><span class="line"> failed = <span class="keyword">false</span>;</span><br><span class="line"> <span class="comment">// 返回这个值</span></span><br><span class="line"> <span class="keyword">return</span> savedState;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalMonitorStateException();</span><br><span class="line"> }</span><br><span class="line"> } <span class="keyword">finally</span> {</span><br><span class="line"> <span class="keyword">if</span> (failed)</span><br><span class="line"> node.waitStatus = Node.CANCELLED;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>判断是否在阻塞队列中</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Returns true if a node, always one that was initially placed on</span></span><br><span class="line"><span class="comment"> * a condition queue, is now waiting to reacquire on sync queue.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> node the node</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> true if is reacquiring</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">isOnSyncQueue</span><span class="params">(Node node)</span> </span>{</span><br><span class="line"> <span class="comment">// 如果waitStatus 是 CONDITION 或者没有 prev 前置节点肯定就不在</span></span><br><span class="line"> <span class="keyword">if</span> (node.waitStatus == Node.CONDITION || node.prev == <span class="keyword">null</span>)</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> <span class="comment">// 这里就是我前面提到的 next 的作用</span></span><br><span class="line"> <span class="keyword">if</span> (node.next != <span class="keyword">null</span>) <span class="comment">// If has successor, it must be on queue</span></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> <span class="comment">// 从 tail 开始找，是否在阻塞队列中</span></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * node.prev can be non-null, but not yet on queue because</span></span><br><span class="line"><span class="comment"> * the CAS to place it on queue can fail. So we have to</span></span><br><span class="line"><span class="comment"> * traverse from tail to make sure it actually made it. It</span></span><br><span class="line"><span class="comment"> * will always be near the tail in calls to this method, and</span></span><br><span class="line"><span class="comment"> * unless the CAS failed (which is unlikely), it will be</span></span><br><span class="line"><span class="comment"> * there, so we hardly ever traverse much.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">return</span> findNodeFromTail(node);</span><br><span class="line">}</span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Returns true if node is on sync queue by searching backwards from tail.</span></span><br><span class="line"><span class="comment"> * Called only when needed by isOnSyncQueue.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> true if present</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">findNodeFromTail</span><span class="params">(Node node)</span> </span>{</span><br><span class="line"> Node t = tail;</span><br><span class="line"> <span class="comment">// 从 tail 开始，从后往前找</span></span><br><span class="line"> <span class="keyword">for</span> (;;) {</span><br><span class="line"> <span class="keyword">if</span> (t == node)</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> <span class="keyword">if</span> (t == <span class="keyword">null</span>)</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> t = t.prev;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>await 的逻辑差不多就是这样子，主要的就是把自己包成一个 Node 节点，waitStatus 的状态是 CONDITION，挂在等待队列的最后，然后完全释放锁，park 等待</p>
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<h2 id="signal"><a href="#signal" class="headerlink" title="signal"></a>signal</h2><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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Moves the longest-waiting thread, if one exists, from the</span></span><br><span class="line"><span class="comment"> * wait queue for this condition to the wait queue for the</span></span><br><span class="line"><span class="comment"> * owning lock.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@throws</span> IllegalMonitorStateException if {<span class="doctag">@link</span> #isHeldExclusively}</span></span><br><span class="line"><span class="comment"> * returns {<span class="doctag">@code</span> false}</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">signal</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (!isHeldExclusively())</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalMonitorStateException();</span><br><span class="line"> <span class="comment">// firstWaiter 肯定是最早开始等待的</span></span><br><span class="line"> Node first = firstWaiter;</span><br><span class="line"> <span class="comment">// 如果不为空就唤醒</span></span><br><span class="line"> <span class="keyword">if</span> (first != <span class="keyword">null</span>)</span><br><span class="line"> doSignal(first);</span><br><span class="line">}</span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Removes and transfers nodes until hit non-cancelled one or</span></span><br><span class="line"><span class="comment"> * null. Split out from signal in part to encourage compilers</span></span><br><span class="line"><span class="comment"> * to inline the case of no waiters.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> first (non-null) the first node on condition queue</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">void</span> <span class="title">doSignal</span><span class="params">(Node first)</span> </span>{</span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> <span class="comment">// 因为要去唤醒 first 节点了，firstWaiter 需要再从后面找一个</span></span><br><span class="line"> <span class="comment">// 并且判断是否为空，如果是空的话就直接可以把 lastWaiter 设置成空了</span></span><br><span class="line"> <span class="keyword">if</span> ( (firstWaiter = first.nextWaiter) == <span class="keyword">null</span>)</span><br><span class="line"> lastWaiter = <span class="keyword">null</span>;</span><br><span class="line"> <span class="comment">// first 不需要继续保存后面的 waiter 了，因为 firstWaiter 已经是 first 的后置节点了</span></span><br><span class="line"> first.nextWaiter = <span class="keyword">null</span>;</span><br><span class="line"> <span class="comment">// 如果 first 节点转移不成功，并且 firstWaiter 节点不为空，则继续进入循环</span></span><br><span class="line"> } <span class="keyword">while</span> (!transferForSignal(first) &&</span><br><span class="line"> (first = firstWaiter) != <span class="keyword">null</span>);</span><br><span class="line">}</span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Transfers a node from a condition queue onto sync queue.</span></span><br><span class="line"><span class="comment"> * Returns true if successful.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> node the node</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> true if successfully transferred (else the node was</span></span><br><span class="line"><span class="comment"> * cancelled before signal)</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">transferForSignal</span><span class="params">(Node node)</span> </span>{</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If cannot change waitStatus, the node has been cancelled.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// 如果状态已经不是 CONDITION 就不会设置成功，返回 false</span></span><br><span class="line"> <span class="keyword">if</span> (!compareAndSetWaitStatus(node, Node.CONDITION, <span class="number">0</span>))</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Splice onto queue and try to set waitStatus of predecessor to</span></span><br><span class="line"><span class="comment"> * indicate that thread is (probably) waiting. If cancelled or</span></span><br><span class="line"><span class="comment"> * attempt to set waitStatus fails, wake up to resync (in which</span></span><br><span class="line"><span class="comment"> * case the waitStatus can be transiently and harmlessly wrong).</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// 调用跟aqs 第一篇中一样的 enq 方法进入阻塞队列，返回入队后的前一节点</span></span><br><span class="line"> Node p = enq(node);</span><br><span class="line"> <span class="keyword">int</span> ws = p.waitStatus;</span><br><span class="line"> <span class="comment">// 将前置节点状态设置成SIGNAL，表示后面有节点在等了</span></span><br><span class="line"> <span class="keyword">if</span> (ws > <span class="number">0</span> || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))</span><br><span class="line"> LockSupport.unpark(node.thread);</span><br><span class="line"> <span class="comment">// 返回 true，上一个方法的循环就退出了</span></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>这里其实就是把 condition 等待队列的第一个未取消的节点入队到阻塞队列去争锁</p>
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<h2 id="附录"><a href="#附录" class="headerlink" title="附录"></a>附录</h2><p><code>synchronized</code> 版的 BoundedBuffer</p>
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<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><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> File: BoundedBuffer.java</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment"> Originally written by Doug Lea and released into the public domain.</span></span><br><span class="line"><span class="comment"> This may be used for any purposes whatsoever without acknowledgment.</span></span><br><span class="line"><span class="comment"> Thanks for the assistance and support of Sun Microsystems Labs,</span></span><br><span class="line"><span class="comment"> and everyone contributing, testing, and using this code.</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment"> History:</span></span><br><span class="line"><span class="comment"> Date Who What</span></span><br><span class="line"><span class="comment"> 11Jun1998 dl Create public version</span></span><br><span class="line"><span class="comment"> 17Jul1998 dl Simplified by eliminating wait counts</span></span><br><span class="line"><span class="comment"> 25aug1998 dl added peek</span></span><br><span class="line"><span class="comment"> 5May1999 dl replace % with conditional (slightly faster)</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">package</span> EDU.oswego.cs.dl.util.concurrent;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Efficient array-based bounded buffer class.</span></span><br><span class="line"><span class="comment"> * Adapted from CPJ, chapter 8, which describes design.</span></span><br><span class="line"><span class="comment"> * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p></span></span><br><span class="line"><span class="comment"> **/</span></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">BoundedBuffer</span> <span class="keyword">implements</span> <span class="title">BoundedChannel</span> </span>{</span><br><span class="line"></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">final</span> Object[] array_; <span class="comment">// the elements</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">int</span> takePtr_ = <span class="number">0</span>; <span class="comment">// circular indices</span></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">int</span> putPtr_ = <span class="number">0</span>; </span><br><span class="line"></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">int</span> usedSlots_ = <span class="number">0</span>; <span class="comment">// length</span></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">int</span> emptySlots_; <span class="comment">// capacity - length</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Helper monitor to handle puts. </span></span><br><span class="line"><span class="comment"> **/</span></span><br><span class="line"> <span class="keyword">protected</span> <span class="keyword">final</span> Object putMonitor_ = <span class="keyword">new</span> Object();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Create a BoundedBuffer with the given capacity.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@exception</span> IllegalArgumentException if capacity less or equal to zero</span></span><br><span class="line"><span class="comment"> **/</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="title">BoundedBuffer</span><span class="params">(<span class="keyword">int</span> capacity)</span> <span class="keyword">throws</span> IllegalArgumentException </span>{</span><br><span class="line"> <span class="keyword">if</span> (capacity <= <span class="number">0</span>) <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException();</span><br><span class="line"> array_ = <span class="keyword">new</span> Object[capacity];</span><br><span class="line"> emptySlots_ = capacity;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Create a buffer with the current default capacity</span></span><br><span class="line"><span class="comment"> **/</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="title">BoundedBuffer</span><span class="params">()</span> </span>{ </span><br><span class="line"> <span class="keyword">this</span>(DefaultChannelCapacity.get()); </span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/** </span></span><br><span class="line"><span class="comment"> * Return the number of elements in the buffer.</span></span><br><span class="line"><span class="comment"> * This is only a snapshot value, that may change</span></span><br><span class="line"><span class="comment"> * immediately after returning.</span></span><br><span class="line"><span class="comment"> **/</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">synchronized</span> <span class="keyword">int</span> <span class="title">size</span><span class="params">()</span> </span>{ <span class="keyword">return</span> usedSlots_; }</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">capacity</span><span class="params">()</span> </span>{ <span class="keyword">return</span> array_.length; }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">incEmptySlots</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">synchronized</span>(putMonitor_) {</span><br><span class="line"> ++emptySlots_;</span><br><span class="line"> putMonitor_.notify();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">synchronized</span> <span class="keyword">void</span> <span class="title">incUsedSlots</span><span class="params">()</span> </span>{</span><br><span class="line"> ++usedSlots_;</span><br><span class="line"> notify();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">insert</span><span class="params">(Object x)</span> </span>{ <span class="comment">// mechanics of put</span></span><br><span class="line"> --emptySlots_;</span><br><span class="line"> array_[putPtr_] = x;</span><br><span class="line"> <span class="keyword">if</span> (++putPtr_ >= array_.length) putPtr_ = <span class="number">0</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">final</span> Object <span class="title">extract</span><span class="params">()</span> </span>{ <span class="comment">// mechanics of take</span></span><br><span class="line"> --usedSlots_;</span><br><span class="line"> Object old = array_[takePtr_];</span><br><span class="line"> array_[takePtr_] = <span class="keyword">null</span>;</span><br><span class="line"> <span class="keyword">if</span> (++takePtr_ >= array_.length) takePtr_ = <span class="number">0</span>;</span><br><span class="line"> <span class="keyword">return</span> old;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> Object <span class="title">peek</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">synchronized</span>(<span class="keyword">this</span>) {</span><br><span class="line"> <span class="keyword">if</span> (usedSlots_ > <span class="number">0</span>)</span><br><span class="line"> <span class="keyword">return</span> array_[takePtr_];</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">null</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">put</span><span class="params">(Object x)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> <span class="keyword">if</span> (x == <span class="keyword">null</span>) <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException();</span><br><span class="line"> <span class="keyword">if</span> (Thread.interrupted()) <span class="keyword">throw</span> <span class="keyword">new</span> InterruptedException();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">synchronized</span>(putMonitor_) {</span><br><span class="line"> <span class="keyword">while</span> (emptySlots_ <= <span class="number">0</span>) {</span><br><span class="line"> <span class="keyword">try</span> { putMonitor_.wait(); }</span><br><span class="line"> <span class="keyword">catch</span> (InterruptedException ex) {</span><br><span class="line"> putMonitor_.notify();</span><br><span class="line"> <span class="keyword">throw</span> ex;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> insert(x);</span><br><span class="line"> }</span><br><span class="line"> incUsedSlots();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">boolean</span> <span class="title">offer</span><span class="params">(Object x, <span class="keyword">long</span> msecs)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> <span class="keyword">if</span> (x == <span class="keyword">null</span>) <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException();</span><br><span class="line"> <span class="keyword">if</span> (Thread.interrupted()) <span class="keyword">throw</span> <span class="keyword">new</span> InterruptedException();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">synchronized</span>(putMonitor_) {</span><br><span class="line"> <span class="keyword">long</span> start = (msecs <= <span class="number">0</span>)? <span class="number">0</span> : System.currentTimeMillis();</span><br><span class="line"> <span class="keyword">long</span> waitTime = msecs;</span><br><span class="line"> <span class="keyword">while</span> (emptySlots_ <= <span class="number">0</span>) {</span><br><span class="line"> <span class="keyword">if</span> (waitTime <= <span class="number">0</span>) <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> <span class="keyword">try</span> { putMonitor_.wait(waitTime); }</span><br><span class="line"> <span class="keyword">catch</span> (InterruptedException ex) {</span><br><span class="line"> putMonitor_.notify();</span><br><span class="line"> <span class="keyword">throw</span> ex;</span><br><span class="line"> }</span><br><span class="line"> waitTime = msecs - (System.currentTimeMillis() - start);</span><br><span class="line"> }</span><br><span class="line"> insert(x);</span><br><span class="line"> }</span><br><span class="line"> incUsedSlots();</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> Object <span class="title">take</span><span class="params">()</span> <span class="keyword">throws</span> InterruptedException </span>{ </span><br><span class="line"> <span class="keyword">if</span> (Thread.interrupted()) <span class="keyword">throw</span> <span class="keyword">new</span> InterruptedException();</span><br><span class="line"> Object old = <span class="keyword">null</span>; </span><br><span class="line"> <span class="keyword">synchronized</span>(<span class="keyword">this</span>) { </span><br><span class="line"> <span class="keyword">while</span> (usedSlots_ <= <span class="number">0</span>) {</span><br><span class="line"> <span class="keyword">try</span> { wait(); }</span><br><span class="line"> <span class="keyword">catch</span> (InterruptedException ex) {</span><br><span class="line"> notify();</span><br><span class="line"> <span class="keyword">throw</span> ex; </span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> old = extract();</span><br><span class="line"> }</span><br><span class="line"> incEmptySlots();</span><br><span class="line"> <span class="keyword">return</span> old;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">public</span> Object <span class="title">poll</span><span class="params">(<span class="keyword">long</span> msecs)</span> <span class="keyword">throws</span> InterruptedException </span>{ </span><br><span class="line"> <span class="keyword">if</span> (Thread.interrupted()) <span class="keyword">throw</span> <span class="keyword">new</span> InterruptedException();</span><br><span class="line"> Object old = <span class="keyword">null</span>; </span><br><span class="line"> <span class="keyword">synchronized</span>(<span class="keyword">this</span>) { </span><br><span class="line"> <span class="keyword">long</span> start = (msecs <= <span class="number">0</span>)? <span class="number">0</span> : System.currentTimeMillis();</span><br><span class="line"> <span class="keyword">long</span> waitTime = msecs;</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">while</span> (usedSlots_ <= <span class="number">0</span>) {</span><br><span class="line"> <span class="keyword">if</span> (waitTime <= <span class="number">0</span>) <span class="keyword">return</span> <span class="keyword">null</span>;</span><br><span class="line"> <span class="keyword">try</span> { wait(waitTime); }</span><br><span class="line"> <span class="keyword">catch</span> (InterruptedException ex) {</span><br><span class="line"> notify();</span><br><span class="line"> <span class="keyword">throw</span> ex; </span><br><span class="line"> }</span><br><span class="line"> waitTime = msecs - (System.currentTimeMillis() - start);</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"> old = extract();</span><br><span class="line"> }</span><br><span class="line"> incEmptySlots();</span><br><span class="line"> <span class="keyword">return</span> old;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="zh-Hans">
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<link itemprop="mainEntityOfPage" href="https://nicksxs.me/2021/02/14/AQS%E7%AF%87%E4%B8%80/">
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<a href="/2021/02/14/AQS%E7%AF%87%E4%B8%80/" class="post-title-link" itemprop="url">AQS篇一</a>
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</h2>
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<span class="post-meta-item-text">Posted on</span>
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<time title="Created: 2021-02-14 22:51:54" itemprop="dateCreated datePublished" datetime="2021-02-14T22:51:54+08:00">2021-02-14</time>
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<span class="post-meta-item-text">Edited on</span>
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<time title="Modified: 2021-02-28 20:02:18" itemprop="dateModified" datetime="2021-02-28T20:02:18+08:00">2021-02-28</time>
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<a href="/categories/Java/" itemprop="url" rel="index"><span itemprop="name">Java</span></a>
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,
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<a href="/categories/Java/%E5%B9%B6%E5%8F%91/" itemprop="url" rel="index"><span itemprop="name">并发</span></a>
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<span id="/2021/02/14/AQS%E7%AF%87%E4%B8%80/" class="post-meta-item leancloud_visitors" data-flag-title="AQS篇一" title="Views">
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<span class="post-meta-item-text">Views: </span>
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<span class="post-meta-item-text">Disqus: </span>
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<span class="post-comments-count disqus-comment-count" data-disqus-identifier="2021/02/14/AQS篇一/" itemprop="commentCount"></span>
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<p>很多东西都是时看时新，而且时间长了也会忘，所以再来复习下，也会有一些新的角度看法这次来聊下AQS的内容，主要是这几个点，</p>
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<h2 id="第一个线程"><a href="#第一个线程" class="headerlink" title="第一个线程"></a>第一个线程</h2><p>第一个线程抢到锁了，此时state跟阻塞队列是怎么样的，其实这里是之前没理解对的地方</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Fair version of tryAcquire. Don't grant access unless</span></span><br><span class="line"><span class="comment"> * recursive call or no waiters or is first.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">tryAcquire</span><span class="params">(<span class="keyword">int</span> acquires)</span> </span>{</span><br><span class="line"> <span class="keyword">final</span> Thread current = Thread.currentThread();</span><br><span class="line"> <span class="keyword">int</span> c = getState();</span><br><span class="line"> <span class="comment">// 这里如果state还是0说明锁还空着</span></span><br><span class="line"> <span class="keyword">if</span> (c == <span class="number">0</span>) {</span><br><span class="line"> <span class="comment">// 因为是公平锁版本的，先去看下是否阻塞队列里有排着队的</span></span><br><span class="line"> <span class="keyword">if</span> (!hasQueuedPredecessors() &&</span><br><span class="line"> compareAndSetState(<span class="number">0</span>, acquires)) {</span><br><span class="line"> <span class="comment">// 没有排队的，并且state使用cas设置成功的就标记当前占有锁的线程是我</span></span><br><span class="line"> setExclusiveOwnerThread(current);</span><br><span class="line"> <span class="comment">// 然后其实就返回了，包括阻塞队列的head和tail节点和waitStatus都没有设置</span></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (current == getExclusiveOwnerThread()) {</span><br><span class="line"> <span class="keyword">int</span> nextc = c + acquires;</span><br><span class="line"> <span class="keyword">if</span> (nextc < <span class="number">0</span>)</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> Error(<span class="string">"Maximum lock count exceeded"</span>);</span><br><span class="line"> setState(nextc);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 这里就是第二个线程会返回false</span></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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<h2 id="第二个线程"><a href="#第二个线程" class="headerlink" title="第二个线程"></a>第二个线程</h2><p>当第二个线程进来的时候应该是怎么样，结合代码来看</p>
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<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Acquires in exclusive mode, ignoring interrupts. Implemented</span></span><br><span class="line"><span class="comment"> * by invoking at least once {<span class="doctag">@link</span> #tryAcquire},</span></span><br><span class="line"><span class="comment"> * returning on success. Otherwise the thread is queued, possibly</span></span><br><span class="line"><span class="comment"> * repeatedly blocking and unblocking, invoking {<span class="doctag">@link</span></span></span><br><span class="line"><span class="comment"> * #tryAcquire} until success. This method can be used</span></span><br><span class="line"><span class="comment"> * to implement method {<span class="doctag">@link</span> Lock#lock}.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> arg the acquire argument. This value is conveyed to</span></span><br><span class="line"><span class="comment"> * {<span class="doctag">@link</span> #tryAcquire} but is otherwise uninterpreted and</span></span><br><span class="line"><span class="comment"> * can represent anything you like.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">acquire</span><span class="params">(<span class="keyword">int</span> arg)</span> </span>{</span><br><span class="line"> <span class="comment">// 前面第一种情况是tryAcquire直接成功了，这个if判断第一个条件就是false，就不往下执行了</span></span><br><span class="line"> <span class="comment">// 如果是第二个线程，第一个条件获取锁不成功，条件判断!tryAcquire(arg) == true，就会走</span></span><br><span class="line"> <span class="comment">// acquireQueued(addWaiter(Node.EXCLUSIVE), arg)</span></span><br><span class="line"> <span class="keyword">if</span> (!tryAcquire(arg) &&</span><br><span class="line"> acquireQueued(addWaiter(Node.EXCLUSIVE), arg))</span><br><span class="line"> selfInterrupt();</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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<p>然后来看下addWaiter的逻辑</p>
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<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="comment">/**</span></span><br><span class="line"><span class="comment"> * Creates and enqueues node for current thread and given mode.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> the new node</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">private</span> Node <span class="title">addWaiter</span><span class="params">(Node mode)</span> </span>{</span><br><span class="line"> <span class="comment">// 这里是包装成一个node</span></span><br><span class="line"> Node node = <span class="keyword">new</span> Node(Thread.currentThread(), mode);</span><br><span class="line"> <span class="comment">// Try the fast path of enq; backup to full enq on failure</span></span><br><span class="line"> <span class="comment">// 最快的方式就是把当前线程的节点放在阻塞队列的最后</span></span><br><span class="line"> Node pred = tail;</span><br><span class="line"> <span class="comment">// 只有当tail，也就是pred不为空的时候可以直接接上</span></span><br><span class="line"> <span class="keyword">if</span> (pred != <span class="keyword">null</span>) {</span><br><span class="line"> node.prev = pred;</span><br><span class="line"> <span class="comment">// 如果这里cas成功了，就直接接上返回了</span></span><br><span class="line"> <span class="keyword">if</span> (compareAndSetTail(pred, node)) {</span><br><span class="line"> pred.next = node;</span><br><span class="line"> <span class="keyword">return</span> node;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 不然就会继续走到这里</span></span><br><span class="line"> enq(node);</span><br><span class="line"> <span class="keyword">return</span> node;</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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<p>然后就是enq的逻辑了</p>
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<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="comment">/**</span></span><br><span class="line"><span class="comment"> * Inserts node into queue, initializing if necessary. See picture above.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> node the node to insert</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> node's predecessor</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">private</span> Node <span class="title">enq</span><span class="params">(<span class="keyword">final</span> Node node)</span> </span>{</span><br><span class="line"> <span class="keyword">for</span> (;;) {</span><br><span class="line"> <span class="comment">// 如果状态没变化的话，tail这时还是null的</span></span><br><span class="line"> Node t = tail;</span><br><span class="line"> <span class="keyword">if</span> (t == <span class="keyword">null</span>) { <span class="comment">// Must initialize</span></span><br><span class="line"> <span class="comment">// 这里就会初始化头结点，就是个空节点</span></span><br><span class="line"> <span class="keyword">if</span> (compareAndSetHead(<span class="keyword">new</span> Node()))</span><br><span class="line"> <span class="comment">// tail也赋值成head</span></span><br><span class="line"> tail = head;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// 这里就设置tail了</span></span><br><span class="line"> node.prev = t;</span><br><span class="line"> <span class="keyword">if</span> (compareAndSetTail(t, node)) {</span><br><span class="line"> t.next = node;</span><br><span class="line"> <span class="keyword">return</span> t;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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<p>所以从这里可以看出来，其实head头结点不是个真实的带有线程的节点，并且不是在第一个线程进来的时候设置的</p>
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<h2 id="解锁"><a href="#解锁" class="headerlink" title="解锁"></a>解锁</h2><p>通过代码来看下</p>
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<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><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Attempts to release this lock.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <p>If the current thread is the holder of this lock then the hold</span></span><br><span class="line"><span class="comment"> * count is decremented. If the hold count is now zero then the lock</span></span><br><span class="line"><span class="comment"> * is released. If the current thread is not the holder of this</span></span><br><span class="line"><span class="comment"> * lock then {<span class="doctag">@link</span> IllegalMonitorStateException} is thrown.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@throws</span> IllegalMonitorStateException if the current thread does not</span></span><br><span class="line"><span class="comment"> * hold this lock</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">unlock</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="comment">// 释放锁</span></span><br><span class="line"> sync.release(<span class="number">1</span>);</span><br><span class="line"> }</span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Releases in exclusive mode. Implemented by unblocking one or</span></span><br><span class="line"><span class="comment"> * more threads if {<span class="doctag">@link</span> #tryRelease} returns true.</span></span><br><span class="line"><span class="comment"> * This method can be used to implement method {<span class="doctag">@link</span> Lock#unlock}.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> arg the release argument. This value is conveyed to</span></span><br><span class="line"><span class="comment"> * {<span class="doctag">@link</span> #tryRelease} but is otherwise uninterpreted and</span></span><br><span class="line"><span class="comment"> * can represent anything you like.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@return</span> the value returned from {<span class="doctag">@link</span> #tryRelease}</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">release</span><span class="params">(<span class="keyword">int</span> arg)</span> </span>{</span><br><span class="line"> <span class="comment">// 尝试去释放</span></span><br><span class="line"> <span class="keyword">if</span> (tryRelease(arg)) {</span><br><span class="line"> Node h = head;</span><br><span class="line"> <span class="keyword">if</span> (h != <span class="keyword">null</span> && h.waitStatus != <span class="number">0</span>)</span><br><span class="line"> unparkSuccessor(h);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> }</span><br><span class="line"><span class="function"><span class="keyword">protected</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">tryRelease</span><span class="params">(<span class="keyword">int</span> releases)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> c = getState() - releases;</span><br><span class="line"> <span class="keyword">if</span> (Thread.currentThread() != getExclusiveOwnerThread())</span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalMonitorStateException();</span><br><span class="line"> <span class="keyword">boolean</span> free = <span class="keyword">false</span>;</span><br><span class="line"> <span class="comment">// 判断是否完全释放锁，因为可重入</span></span><br><span class="line"> <span class="keyword">if</span> (c == <span class="number">0</span>) {</span><br><span class="line"> free = <span class="keyword">true</span>;</span><br><span class="line"> setExclusiveOwnerThread(<span class="keyword">null</span>);</span><br><span class="line"> }</span><br><span class="line"> setState(c);</span><br><span class="line"> <span class="keyword">return</span> free;</span><br><span class="line"> }</span><br><span class="line"><span class="comment">// 这段代码和上面的一致，只是为了顺序性，又拷下来看下</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">release</span><span class="params">(<span class="keyword">int</span> arg)</span> </span>{</span><br><span class="line"> <span class="comment">// 尝试去释放，如果是完全释放，返回的就是true，否则是false</span></span><br><span class="line"> <span class="keyword">if</span> (tryRelease(arg)) {</span><br><span class="line"> Node h = head;</span><br><span class="line"> <span class="comment">// 这里判断头结点是否为空以及waitStatus的状态，前面说了head节点其实是</span></span><br><span class="line"> <span class="comment">// 在第二个线程进来的时候初始化的，如果是空的话说明没后续节点，并且waitStatus</span></span><br><span class="line"> <span class="comment">// 也表示了后续的等待状态</span></span><br><span class="line"> <span class="keyword">if</span> (h != <span class="keyword">null</span> && h.waitStatus != <span class="number">0</span>)</span><br><span class="line"> unparkSuccessor(h);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">true</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Wakes up node's successor, if one exists.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param</span> node the node</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="comment">// 唤醒后继节点</span></span><br><span class="line"> <span class="function"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title">unparkSuccessor</span><span class="params">(Node node)</span> </span>{</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If status is negative (i.e., possibly needing signal) try</span></span><br><span class="line"><span class="comment"> * to clear in anticipation of signalling. It is OK if this</span></span><br><span class="line"><span class="comment"> * fails or if status is changed by waiting thread.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">int</span> ws = node.waitStatus;</span><br><span class="line"> <span class="keyword">if</span> (ws < <span class="number">0</span>)</span><br><span class="line"> compareAndSetWaitStatus(node, ws, <span class="number">0</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Thread to unpark is held in successor, which is normally</span></span><br><span class="line"><span class="comment"> * just the next node. But if cancelled or apparently null,</span></span><br><span class="line"><span class="comment"> * traverse backwards from tail to find the actual</span></span><br><span class="line"><span class="comment"> * non-cancelled successor.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> Node s = node.next;</span><br><span class="line"> <span class="comment">// 如果后继节点是空或者当前节点取消等待了</span></span><br><span class="line"> <span class="keyword">if</span> (s == <span class="keyword">null</span> || s.waitStatus > <span class="number">0</span>) {</span><br><span class="line"> s = <span class="keyword">null</span>;</span><br><span class="line"> <span class="comment">// 从后往前找，找到非取消的节点，注意这里不是找到就退出，而是一直找到头</span></span><br><span class="line"> <span class="comment">// 所以不必担心中间有取消的</span></span><br><span class="line"> <span class="keyword">for</span> (Node t = tail; t != <span class="keyword">null</span> && t != node; t = t.prev)</span><br><span class="line"> <span class="keyword">if</span> (t.waitStatus <= <span class="number">0</span>)</span><br><span class="line"> s = t;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> (s != <span class="keyword">null</span>)</span><br><span class="line"> <span class="comment">// 将其唤醒</span></span><br><span class="line"> LockSupport.unpark(s.thread);</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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href="/tags/%E6%A4%8D%E7%89%A9%E5%9B%AD/" rel="tag">植物园</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B2%99%E8%8C%B6%E9%9D%A2/" rel="tag">沙茶面</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B3%A8%E8%A7%A3/" rel="tag">注解</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B5%B7%E8%9B%8E%E7%85%8E/" rel="tag">海蛎煎</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%B6%88%E6%81%AF%E9%98%9F%E5%88%97/" rel="tag">消息队列</a><span class="tag-list-count">4</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%BA%90%E7%A0%81/" rel="tag">源码</a><span class="tag-list-count">11</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E6%BA%90%E7%A0%81%E8%A7%A3%E6%9E%90/" rel="tag">源码解析</a><span 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href="/tags/%E7%BC%93%E5%AD%98%E5%87%BB%E7%A9%BF/" rel="tag">缓存击穿</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%BC%93%E5%AD%98%E7%A9%BF%E9%80%8F/" rel="tag">缓存穿透</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%BC%93%E5%AD%98%E9%9B%AA%E5%B4%A9/" rel="tag">缓存雪崩</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%BE%8E%E5%9B%BD/" rel="tag">美国</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%87%AA%E9%80%82%E5%BA%94%E6%8B%93%E5%B1%95/" rel="tag">自适应拓展</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%A7%84%E5%88%99/" rel="tag">规则</a><span class="tag-list-count">3</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/" rel="tag">设计模式</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AF%BB%E4%B9%A6/" rel="tag">读书</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AF%BB%E5%90%8E%E6%84%9F/" rel="tag">读后感</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%B6%B3%E7%90%83/" rel="tag">足球</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%B7%91%E6%AD%A5/" rel="tag">跑步</a><span class="tag-list-count">6</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%B7%AF%E6%94%BF%E8%A7%84%E5%88%92/" rel="tag">路政规划</a><span class="tag-list-count">2</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%BD%AC%E4%B9%89/" rel="tag">转义</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%BF%90%E5%8A%A8/" rel="tag">运动</a><span class="tag-list-count">6</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E9%80%92%E5%BD%92/" rel="tag">递归</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E9%A2%98%E8%A7%A3/" rel="tag">题解</a><span class="tag-list-count">9</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E9%A9%AC%E6%88%8F%E5%9B%A2/" rel="tag">马戏团</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E9%AB%98%E9%80%9F/" rel="tag">高速</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E9%BC%93%E6%B5%AA%E5%B1%BF/" rel="tag">鼓浪屿</a><span class="tag-list-count">1</span></li></ul>
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<div class="links-of-blogroll motion-element">
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|
<div class="links-of-blogroll-title"><i class="fa fa-link fa-fw"></i>
|
|
Links
|
|
</div>
|
|
<ul class="links-of-blogroll-list">
|
|
<li class="links-of-blogroll-item">
|
|
<a href="https://covermusic.cn/" title="https://covermusic.cn" rel="noopener" target="_blank">69伙伴</a>
|
|
</li>
|
|
</ul>
|
|
</div>
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</div>
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|
|
</div>
|
|
</aside>
|
|
<div id="sidebar-dimmer"></div>
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|
|
|
|
|
</div>
|
|
</main>
|
|
|
|
<footer class="footer">
|
|
<div class="footer-inner">
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|
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|
|
|
<div class="copyright">
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|
|
©
|
|
<span itemprop="copyrightYear">2021</span>
|
|
<span class="with-love">
|
|
<i class="fa fa-heart"></i>
|
|
</span>
|
|
<span class="author" itemprop="copyrightHolder">Nicksxs</span>
|
|
</div>
|
|
<div class="powered-by">Powered by <a href="https://hexo.io/" class="theme-link" rel="noopener" target="_blank">Hexo</a> & <a href="https://pisces.theme-next.org/" class="theme-link" rel="noopener" target="_blank">NexT.Pisces</a>
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</div>
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|
|
<div class="busuanzi-count">
|
|
<script async src="https://busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
|
|
<span class="post-meta-item" id="busuanzi_container_site_uv" style="display: none;">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-user"></i>
|
|
</span>
|
|
<span class="site-uv" title="Total Visitors">
|
|
<span id="busuanzi_value_site_uv"></span>
|
|
</span>
|
|
</span>
|
|
<span class="post-meta-divider">|</span>
|
|
<span class="post-meta-item" id="busuanzi_container_site_pv" style="display: none;">
|
|
<span class="post-meta-item-icon">
|
|
<i class="fa fa-eye"></i>
|
|
</span>
|
|
<span class="site-pv" title="Total Views">
|
|
<span id="busuanzi_value_site_pv"></span>
|
|
</span>
|
|
</span>
|
|
</div>
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|
|
|
|
|
|
<script>
|
|
(function() {
|
|
function leancloudSelector(url) {
|
|
url = encodeURI(url);
|
|
return document.getElementById(url).querySelector('.leancloud-visitors-count');
|
|
}
|
|
|
|
function addCount(Counter) {
|
|
var visitors = document.querySelector('.leancloud_visitors');
|
|
var url = decodeURI(visitors.id);
|
|
var title = visitors.dataset.flagTitle;
|
|
|
|
Counter('get', '/classes/Counter?where=' + encodeURIComponent(JSON.stringify({ url })))
|
|
.then(response => response.json())
|
|
.then(({ results }) => {
|
|
if (results.length > 0) {
|
|
var counter = results[0];
|
|
leancloudSelector(url).innerText = counter.time + 1;
|
|
Counter('put', '/classes/Counter/' + counter.objectId, { time: { '__op': 'Increment', 'amount': 1 } })
|
|
.catch(error => {
|
|
console.error('Failed to save visitor count', error);
|
|
});
|
|
} else {
|
|
leancloudSelector(url).innerText = 'Counter not initialized! More info at console err msg.';
|
|
console.error('ATTENTION! LeanCloud counter has security bug, see how to solve it here: https://github.com/theme-next/hexo-leancloud-counter-security. \n However, you can still use LeanCloud without security, by setting `security` option to `false`.');
|
|
|
|
}
|
|
})
|
|
.catch(error => {
|
|
console.error('LeanCloud Counter Error', error);
|
|
});
|
|
}
|
|
|
|
function showTime(Counter) {
|
|
var visitors = document.querySelectorAll('.leancloud_visitors');
|
|
var entries = [...visitors].map(element => {
|
|
return decodeURI(element.id);
|
|
});
|
|
|
|
Counter('get', '/classes/Counter?where=' + encodeURIComponent(JSON.stringify({ url: { '$in': entries } })))
|
|
.then(response => response.json())
|
|
.then(({ results }) => {
|
|
for (let url of entries) {
|
|
let target = results.find(item => item.url === url);
|
|
leancloudSelector(url).innerText = target ? target.time : 0;
|
|
}
|
|
})
|
|
.catch(error => {
|
|
console.error('LeanCloud Counter Error', error);
|
|
});
|
|
}
|
|
|
|
let { app_id, app_key, server_url } = {"enable":true,"app_id":"ysza182Vghlqjdt7QiwGLLJy-gzGzoHsz","app_key":"s9GDqbn7gnGGkusf66YRVccw","server_url":"https://leancloud.cn","security":true};
|
|
function fetchData(api_server) {
|
|
var Counter = (method, url, data) => {
|
|
return fetch(`${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>
|
|
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|
|
|
|
<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>
|