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JUC-CyclicBarrier.html
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JUC-CyclicBarrier.html
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NexT=window.NexT||{},CONFIG={root:"/",scheme:"Mist",sidebar:{position:"left",display:"always",offset:12,offset_float:0,b2t:!1,scrollpercent:!0},fancybox:!1,motion:!1}</script><title>JUC之CyclicBarrier | MrBird</title></head><body ondragstart="return!1" class="animsition" lang="zh-Hans" style="overflow-x:hidden;padding-left:280px"><script type="text/javascript" src="/js/mo.min.js"></script><style>body{text-rendering:geometricPrecision!important;font-family:'Josefin Sans','PingFang SC'!important;-webkit-font-smoothing:antialiased!important;-webkit-text-size-adjust:100%!important;background-color:#f4f6f7}@media (min-width:768px) and (max-width:991px){body .header-innerr{width:700px!important}}.header-innerr{margin:0 auto;padding:100px 0 70px;width:880px}@media (min-width:1600px){.container .header-innerr{width:996px}}.header-innerr{position:relative}.header-innerr{padding:0}.header-innerr:after,.header-innerr:before{content:" ";display:table}.header-innerr:after{clear:both}@media (max-width:767px){.header-innerr{width:auto;padding:10px;margin-bottom:-20px}}</style><div class="container sidebar-position-left page-post-detail"><div class="headband"></div><header id="header" class="header"><div class="header-inner"><div class="site-brand-wrapper"><div class="site-meta"><link href="https://fonts.font.im/css?family=Merienda" rel="stylesheet"><div class="custom-logo-site-title"></div><h1 class="site-subtitle" itemprop="description"></h1></div><div class="site-nav-toggle"><button><span class="btn-bar"></span> <span class="btn-bar"></span> <span class="btn-bar"></span></button></div></div><nav class="site-nav"><div class="site-search"><div class="popup search-popup local-search-popup"><div class="local-search-header clearfix"><span class="search-icon"><i class="fa fa-search"></i> </span><span class="popup-btn-close"><i class="fa fa-times-circle"></i></span><div class="local-search-input-wrapper"><input autocomplete="off" placeholder="Search" spellcheck="false" type="text" id="local-search-input"></div></div><div id="local-search-result"></div></div></div></nav></div><div class="header-innerr"></div></header><main id="main" class="main"><div class="main-inner"><div class="content-wrap"><div id="content" class="content"><div id="posts" class="posts-expand"><article class="post post-type-normal" itemscope itemtype="http://schema.org/Article"><link itemprop="mainEntityOfPage" href="http://mrbird.cc/JUC-CyclicBarrier.html"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="name" content="MrBird"><meta itemprop="description" content=""><meta itemprop="image" content="/images/blogImage.jpg"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="MrBird"></span><header class="post-header"><h2 class="post-title" itemprop="name headline">JUC之CyclicBarrier</h2><div class="post-meta"><span class="post-time"><span class="post-meta-item-icon"><i class="fa fa-calendar-o"></i> </span><span class="post-meta-item-text"></span> <time title="创建于" itemprop="dateCreated datePublished" datetime="2019-03-03T16:23:58+08:00">2019-03-03 </time></span><span></span> <span class="post-meta-divider">|</span> <span class="page-pv"><i class="fa fa-laptop"></i> Visit count <span class="busuanzi-value" id="busuanzi_value_page_pv"></span></span></div></header><div class="post-body" itemprop="articleBody"><p>CyclicBarrier的字面意思是可循环使用（Cyclic）的屏障（Barrier）。它要做的事情是，让一组线程到达一个屏障（也可以叫同步点）时被阻塞，直到最后一个线程到达屏障时，屏障才会开门，所有被屏障拦截的线程才会继续运行。CyclicBarrier默认的构造方法是<code>CyclicBarrier(int parties)</code>，其参数表示屏障拦截的线程数量，每个线程调用<code>await</code>方法告诉CyclicBarrier我已经到达了屏障，然后当前线程被阻塞。</p><a id="more"></a><h2 id="CyclicBarrier示例"><a href="#CyclicBarrier示例" class="headerlink" title="CyclicBarrier示例"></a>CyclicBarrier示例</h2><p>使用“人满发车”的例子来演示CyclicBarrier：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></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">CyclicBarrierTest</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>);</span><br><span class="line"> System.out.println(<span class="string">"快上车来不及解释了"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">5</span>);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"已上车"</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(<span class="string">"所有人已上车，发车"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"Jane"</span>).start();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"已上车"</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(<span class="string">"所有人已上车，发车"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"Mike"</span>).start();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>上面例子中我们定义了一个等待2个线程完成的CyclicBarrier，在两个线程内部调用了<code>await</code>方法，让其阻塞等待，并告知CyclicBarrier我已经到达屏障了。只有当两个线程都执行到<code>barrier.await()</code>这一行时，屏障开启，线程才会继续往下执行。程序输出如下所示：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">快上车来不及解释了</span><br><span class="line">Thread[Mike,5,main]已上车</span><br><span class="line">Thread[Jane,5,main]已上车</span><br><span class="line">所有人已上车，发车</span><br><span class="line">所有人已上车，发车</span><br></pre></td></tr></table></figure><p></p><p>CyclicBarrier的构造函数支持传入一个回调方法：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(n, () -> {</span><br><span class="line"> System.out.println(<span class="string">"当所有线程到达屏障时，执行该回调"</span>);</span><br><span class="line">});</span><br></pre></td></tr></table></figure><p></p><p>改造上面的例子：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></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">CyclicBarrierTest</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>, <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> System.out.println(<span class="string">"发车，嘟嘟嘟"</span>);</span><br><span class="line"> }));</span><br><span class="line"></span><br><span class="line"> System.out.println(<span class="string">"快上车来不及解释了"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">5</span>);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"已上车"</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(<span class="string">"所有人已上车"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"Jane"</span>).start();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"已上车"</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(<span class="string">"所有人已上车"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"Mike"</span>).start();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>输出如下所示：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">快上车来不及解释了</span><br><span class="line">Thread[Mike,5,main]已上车</span><br><span class="line">Thread[Jane,5,main]已上车</span><br><span class="line">发车，嘟嘟嘟</span><br><span class="line">所有人已上车，发车</span><br><span class="line">所有人已上车，发车</span><br></pre></td></tr></table></figure><p></p><h2 id="设置超时时间"><a href="#设置超时时间" class="headerlink" title="设置超时时间"></a>设置超时时间</h2><p><code>await</code>的重载方法：<code>await(long timeout, TimeUnit unit)</code>可以设置最大等待时长，超出这个时间屏障还没有开启的话则抛出<code>TimeoutException</code>：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></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">CyclicBarrierTest2</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread1"</span>).start();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> barrier.await(<span class="number">1</span>, TimeUnit.SECONDS);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> } <span class="keyword">catch</span> (TimeoutException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread2"</span>).start();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p><img src="img/QQ截图20190513104938.png" alt="QQ截图20190513104938.png"></p><p><img src="img/QQ截图20190513105045.png" alt="QQ截图20190513105045.png"></p><h2 id="BrokenBarrierException"><a href="#BrokenBarrierException" class="headerlink" title="BrokenBarrierException"></a>BrokenBarrierException</h2><p>抛出<code>BrokenBarrierException</code>异常时表示屏障破损，此时标志位broken=true。抛出<code>BrokenBarrierException</code>异常的情况主要有：</p><ol><li><p>其他等待的线程被中断，则当前线程抛出<code>BrokenBarrierException</code>异常；</p></li><li><p>其他等待的线程超时，则当前线程抛出<code>BrokenBarrierException</code>异常；</p></li><li><p>当前线程在等待时，其他线程调用CyclicBarrier.reset()方法，则当前线程抛出BrokenBarrierException异常。</p></li></ol><p>模拟第1种情况，其他等待的线程被中断，则当前线程抛出<code>BrokenBarrierException</code>异常：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></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">CyclicBarrierTest2</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread1"</span>).start();</span><br><span class="line"></span><br><span class="line"> Thread thread2 = <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">1</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread2"</span>);</span><br><span class="line"></span><br><span class="line"> thread2.start();</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">2</span>);</span><br><span class="line"> thread2.interrupt();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>输出：</p><p><img src="img/QQ截图20190513112642.png" alt="QQ截图20190513112642.png"></p><p>上面例子中thread2线程睡眠1秒后先到达屏障点，然后进入等待状态。2秒后main线程执行<code>thread2.interrupt()</code>中断等待中的thread2线程，所以程序抛出<code>BrokenBarrierException</code>异常。3秒后thread1线程到达屏障点，此时屏障已经被破坏了，所以也抛出<code>BrokenBarrierException</code>异常。</p><p>模拟第2种情况：其他等待的线程超时，则当前线程抛出<code>BrokenBarrierException</code>异常：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></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">CyclicBarrierTest2</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread1"</span>).start();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">1</span>);</span><br><span class="line"> barrier.await(<span class="number">1</span>, TimeUnit.SECONDS);</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException | TimeoutException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread2"</span>).start();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>输出：</p><p><img src="img/QQ截图20190513113514.png" alt="QQ截图20190513113514.png"></p><p>上面例子中thread2睡眠1秒后到达屏障点，然后进入等待状态（最多等待1秒），然而因为thread1要3秒后才能到达屏障点，所以thread2将抛出<code>TimeoutException</code>。3秒后，thread1到达屏障点，但这时候由于thread2的<code>await</code>方法抛出的异常破坏了屏障，所以thread1将抛出<code>BrokenBarrierException</code>异常。</p><p>模拟第3中情况：当前线程在等待时，其他线程调用CyclicBarrier.reset()方法，则当前线程抛出BrokenBarrierException异常：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></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">CyclicBarrierTest2</span> </span>{</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>{</span><br><span class="line"> CyclicBarrier barrier = <span class="keyword">new</span> CyclicBarrier(<span class="number">2</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">3</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread1"</span>).start();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span> Thread(() -> {</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"></span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"开始执行"</span>);</span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">1</span>);</span><br><span class="line"> barrier.await();</span><br><span class="line"> System.out.println(Thread.currentThread() + <span class="string">"继续执行"</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (InterruptedException | BrokenBarrierException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }, <span class="string">"thread2"</span>).start();</span><br><span class="line"></span><br><span class="line"> TimeUnit.SECONDS.sleep(<span class="number">2</span>);</span><br><span class="line"> System.out.println(barrier.getNumberWaiting());</span><br><span class="line"> barrier.reset();</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>输出：</p><p><img src="img/QQ截图20190513114412.png" alt="QQ截图20190513114412.png"></p><p>上面例子中，thread2睡眠1秒后到达屏障点，然后进入等待状态。2秒后main线程调用<code>reset</code>方法重置了屏障，所以在等待状态中的thread2抛出<code>BrokenBarrierException</code>异常。3秒后，thread1到达屏障点，由于<code>reset</code>方法重置了屏障，所以thread1并不会抛出<code>BrokenBarrierException</code>异常，而是一直在屏障点进行等待别的线程到达屏障点。</p><p><strong>从上面的三个例子中可以看到，无论是哪种情况导致屏障破坏，屏障点后面的代码都没有被执行，main方法也没有退出。</strong></p><h2 id="和CountDownLatch区别"><a href="#和CountDownLatch区别" class="headerlink" title="和CountDownLatch区别"></a>和CountDownLatch区别</h2><ol><li><p>CountDownLatch：一个线程(或者多个)，等待另外N个线程完成某个事情之后才能执行；CyclicBarrier：N个线程相互等待，任何一个线程完成之前，所有的线程都必须等待。</p></li><li><p>CountDownLatch：一次性的；CyclicBarrier：可以重复使用。</p></li></ol><script>$(".post-body a").not(".thispage").addClass("ignore-href").attr("target","_blank")</script></div><div></div><div><div style="padding:10px 0;margin:20px auto;width:90%;text-align:center;color:#878787" id="reward-div"><div>请作者喝瓶肥宅水🥤</div><button id="rewardButton" style="margin-top:10px" disable="enable" onclick='var e=document.getElementById("QR");"none"===e.style.display?e.style.display="block":e.style.display="none"'><span style="height:46px;width:46px;line-height:46px;border-radius:50%;color:#fe5f55;font-weight:600;background:#ffd5be;border:none;box-shadow:0 4px 8px 0 rgba(255,213,190,.4)">￥</span></button><div id="QR" style="display:none"><div id="wechat" style="display:inline-block"><img id="wechat_qr" src="/img/wechat_pay.png" 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itemscope itemtype="https://mrbird.cc"><div class="author__header"><div class="author__avatar"><img src="/images/blogImage.jpg" class="author__avatar" alt="MrBird" itemprop="image"></div><div class="author__content"><div class="author__name" itemprop="name">MrBird</div><p class="author__bio" itemprop="description">A simple blog, code repository, just keep blogging</p></div><div class="author__count"><a href="/archives" class="ignore-href"><span class="count">14</span> <span>Archives</span> </a><a href="/tags" class="ignore-href"><span class="count">2</span> <span>Labels</span></a></div></div><div class="author__urls-wrapper"><ul class="author__urls social-icons"><li><a href="/" itemprop="url" class="ignore-href">🏠 Home</a></li><li><a href="/archives" itemprop="url" class="ignore-href">📦 Archives</a></li><li><a href="/tags" itemprop="url" class="ignore-href">🔖 Labels</a></li><li><a href="/friends" itemprop="url" class="ignore-href">👬 Friends</a></li><li><a href="javascript:;" 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