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并发编程.html
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<!doctype html>
<html>
<head>
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</style><title>并发编程的艺术总结</title>
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<body class='typora-export os-windows'><div class='typora-export-content'>
<div id='write' class=''><h1 id='并发编程总结'><span>并发编程总结</span></h1><p> </p><h2 id='11-java中的13个原子操作类'><span>1.1 Java中的13个原子操作类</span></h2><p><span> </span><span>当程序更新一个变量时，如果多线程同时更新这个变量，可能得到期望之外的值，比如变量i=1，A线程更新i+1，B线程也更新i+1，经过两个线程操作之后可能i不等于3，而是等于2。因为A和B线程在更新变量i的时候拿到的i都是1，这就是线程不安全的更新操作，</span><strong><span>通常我们会使用synchronized来解决这个问题，synchronized会保证多线程不会同时更新变量i。</span></strong></p><p><span> </span><span>而Java从JDK 1.5开始提供了java.util.concurrent.atomic包（以下简称Atomic包），这个包中的原子操作类提供了一种用法简单、性能高效、线程安全地更新一个变量的方式。Atomic包里的类基本都是使用Unsafe实现的包装类。</span></p><h3 id='111-原子更新基本类型类'><span>1.1.1 原子更新基本类型类</span></h3><p><span>使用原子的方式更新基本类型，Atomic包提供了以下3个类。</span></p><p><span>·AtomicBoolean：原子更新布尔类型。</span>
<span>·AtomicInteger：原子更新整型。</span>
<span>·AtomicLong：原子更新长整型。</span></p><p><span>以上3个类提供的方法几乎一模一样，所以本节仅以AtomicInteger为例进行讲解，AtomicInteger的常用方法如下。</span></p><p><span>下面是使用 </span><code>AtomicInteger</code><span> 的一个简单示例：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">atomic</span>.<span class="cm-variable">AtomicInteger</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">AtomicIntegerExample</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">0</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 并发递增</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-number">10</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span> <span class="cm-variable">thread</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(() <span class="cm-operator">-></span> {</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">newValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">incrementAndGet</span>();</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Incremented value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">newValue</span>);</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> });</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">thread</span>.<span class="cm-variable">start</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 等待所有线程完成</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span>.<span class="cm-variable">sleep</span>(<span class="cm-number">1000</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">InterruptedException</span> <span class="cm-variable">e</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">e</span>.<span class="cm-variable">printStackTrace</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 获取最终的计数器值</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">finalValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Final value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">finalValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 706px;"></div><div class="CodeMirror-gutters" style="display: none; height: 706px;"></div></div></div></pre><p><span>在这个示例中，我们创建了一个 </span><code>AtomicInteger</code><span> 对象 </span><code>counter</code><span>，并初始化为 0。然后，我们创建了 10 个线程，并通过 </span><code>incrementAndGet</code><span> 方法对计数器进行并发递增操作。</span></p><p><span>每个线程都会调用 </span><code>incrementAndGet</code><span> 方法，该方法会原子地递增计数器的值，并返回递增后的值。在每个线程中，我们输出递增后的值。</span></p><p><span>最后，我们通过调用 </span><code>counter.get()</code><span> 获取最终的计数器值，并输出到控制台。</span></p><p><strong><span>由于 </span><code>AtomicInteger</code><span> 是线程安全的，它能够确保在并发环境下对计数器的递增操作是原子的，避免了数据竞争和不一致性的问题。因此，最终的计数器值应该是 10。</span></strong></p><p><span>这个示例展示了 </span><code>AtomicInteger</code><span> 的一个常见用法，即在多线程环境中进行安全的计数操作。它可以在各种并发场景中使用，如任务计数、线程池管理等。</span></p><p><code>AtomicInteger</code><span> 类提供了一系列方法来进行原子性的整数操作。以下是一些常用的方法：</span></p><ol start='' ><li><code>int get()</code><span>: 返回当前的整数值。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">value</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Current value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">value</span>);</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 78px;"></div><div class="CodeMirror-gutters" style="display: none; height: 78px;"></div></div></div></pre><ol start='2' ><li><code>void set(int newValue)</code><span>: 设置新的整数值。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">counter</span>.<span class="cm-variable">set</span>(<span class="cm-number">20</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Updated value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>());</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 78px;"></div><div class="CodeMirror-gutters" style="display: none; height: 78px;"></div></div></div></pre><ol start='3' ><li><code>int getAndSet(int newValue)</code><span>: 设置新的整数值，并返回旧的值。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">oldValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">getAndSet</span>(<span class="cm-number">20</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Old value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">oldValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Updated value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>());</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 105px;"></div><div class="CodeMirror-gutters" style="display: none; height: 105px;"></div></div></div></pre><ol start='4' ><li><code>int incrementAndGet()</code><span>: 将当前值加一，并返回递增后的值。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">newValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">incrementAndGet</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Incremented value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">newValue</span>);</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 78px;"></div><div class="CodeMirror-gutters" style="display: none; height: 78px;"></div></div></div></pre><ol start='5' ><li><code>int decrementAndGet()</code><span>: 将当前值减一，并返回递减后的值。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">newValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">decrementAndGet</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Decremented value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">newValue</span>);</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 78px;"></div><div class="CodeMirror-gutters" style="display: none; height: 78px;"></div></div></div></pre><ol start='6' ><li><code>int getAndIncrement()</code><span>: 返回当前值，并将值加一。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">oldValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">getAndIncrement</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Old value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">oldValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Incremented value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>());</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 105px;"></div><div class="CodeMirror-gutters" style="display: none; height: 105px;"></div></div></div></pre><ol start='7' ><li><code>int getAndDecrement()</code><span>: 返回当前值，并将值减一。</span></li></ol><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">AtomicInteger</span> <span class="cm-variable">counter</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicInteger</span>(<span class="cm-number">10</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">oldValue</span> <span class="cm-operator">=</span> <span class="cm-variable">counter</span>.<span class="cm-variable">getAndDecrement</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Old value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">oldValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Decremented value: "</span> <span class="cm-operator">+</span> <span class="cm-variable">counter</span>.<span class="cm-variable">get</span>());</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 105px;"></div><div class="CodeMirror-gutters" style="display: none; height: 105px;"></div></div></div></pre><p><span>除了上述方法之外，</span><code>AtomicInteger</code><span> 还提供了其他方法，如 </span><code>compareAndSet()</code><span>, </span><code>getAndUpdate()</code><span>, </span><code>updateAndGet()</code><span> 等，用于进行比较和更新操作，以及一些位运算方法。</span></p><p><span>这些方法保证了对整数的操作是原子性的，可以在多线程环境下安全地进行操作，避免了数据竞争和不一致性的问题。</span></p><p><strong><span>那么getAndIncrement是如何实现原子操作的呢？让我们一起分析其实现原理。</span></strong></p><p><span>getAndIncrement的源码如下：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">final</span> <span class="cm-variable-3">int</span> <span class="cm-def">getAndIncrement</span>() {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span> (;;) {</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">current</span> <span class="cm-operator">=</span> <span class="cm-variable">get</span>();</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">next</span> <span class="cm-operator">=</span> <span class="cm-variable">current</span> <span class="cm-operator">+</span> <span class="cm-number">1</span>;</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">if</span> (<span class="cm-variable">compareAndSet</span>(<span class="cm-variable">current</span>, <span class="cm-variable">next</span>))</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">return</span> <span class="cm-variable">current</span>;</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">} </span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">final</span> <span class="cm-variable-3">boolean</span> <span class="cm-def">compareAndSet</span>(<span class="cm-variable-3">int</span> <span class="cm-variable">expect</span>, <span class="cm-variable-3">int</span> <span class="cm-variable">update</span>) {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">return</span> <span class="cm-variable">unsafe</span>.<span class="cm-variable">compareAndSwapInt</span>(<span class="cm-keyword">this</span>, <span class="cm-variable">valueOffset</span>, <span class="cm-variable">expect</span>, <span class="cm-variable">update</span>);</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// this是要进行比较的对象为当前对象</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 316px;"></div><div class="CodeMirror-gutters" style="display: none; height: 316px;"></div></div></div></pre><p><span>Atomic包里的类基本都是使用Unsafe实现的，让我们一起看一下Unsafe的源码，如下列代码清单所示。</span></p><p><span> </span><span>Atomic包提供了3种基本类型的原子更新，但是Java的基本类型里还有char、float和double等。那么问题来了，如何原子的更新其他的基本类型呢？</span></p><p><span> </span><span>再看AtomicBoolean源码，发现它是先把Boolean转换成整型，再使用compareAndSwapInt进行CAS，所以原子更新char、float和double变量也可以用类似的思路来实现。</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">/**</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">* 如果当前数值是expected，则原子的将Java变量更新成x</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">* @return 如果更新成功则返回true</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">*/</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">final</span> <span class="cm-keyword">native</span> <span class="cm-variable-3">boolean</span> <span class="cm-def">compareAndSwapObject</span>(<span class="cm-variable-3">Object</span> <span class="cm-variable">o</span>,</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">long</span> <span class="cm-variable">offset</span>,</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">Object</span> <span class="cm-variable">expected</span>,</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">Object</span> <span class="cm-variable">x</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">final</span> <span class="cm-keyword">native</span> <span class="cm-variable-3">boolean</span> <span class="cm-def">compareAndSwapInt</span>(<span class="cm-variable-3">Object</span> <span class="cm-variable">o</span>, <span class="cm-variable-3">long</span> <span class="cm-variable">offset</span>,</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">expected</span>,</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">x</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">final</span> <span class="cm-keyword">native</span> <span class="cm-variable-3">boolean</span> <span class="cm-def">compareAndSwapLong</span>(<span class="cm-variable-3">Object</span> <span class="cm-variable">o</span>, <span class="cm-variable-3">long</span> <span class="cm-variable">offset</span>,</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">long</span> <span class="cm-variable">expected</span>,</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">long</span> <span class="cm-variable">x</span>);</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 366px;"></div><div class="CodeMirror-gutters" style="display: none; height: 366px;"></div></div></div></pre><h3 id='112-原子更新数组'><span>1.1.2 原子更新数组</span></h3><p><strong><span>通过原子的方式更新数组里的某个元素，Atomic包提供了以下4个类。</span></strong>
<span>·AtomicIntegerArray：原子更新整型数组里的元素。</span>
<span>·AtomicLongArray：原子更新长整型数组里的元素。</span>
<span>·AtomicReferenceArray：原子更新引用类型数组里的元素。</span></p><p><span>在 Java 中，可以使用 </span><code>AtomicIntegerArray</code><span> 类来实现原子更新数组的操作。</span><code>AtomicIntegerArray</code><span> 是 </span><code>java.util.concurrent.atomic</code><span> 包下的一个类，它提供了原子操作来更新整数数组的元素。</span></p><p><span>下面是原子更新数组的一些常见操作的示例：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">atomic</span>.<span class="cm-variable">AtomicIntegerArray</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">AtomicIntegerArrayExample</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span>[] <span class="cm-variable">array</span> <span class="cm-operator">=</span> {<span class="cm-number">1</span>, <span class="cm-number">2</span>, <span class="cm-number">3</span>, <span class="cm-number">4</span>, <span class="cm-number">5</span>};</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">AtomicIntegerArray</span> <span class="cm-variable">atomicArray</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">AtomicIntegerArray</span>(<span class="cm-variable">array</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 获取指定索引处的元素</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">value</span> <span class="cm-operator">=</span> <span class="cm-variable">atomicArray</span>.<span class="cm-variable">get</span>(<span class="cm-number">2</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Value at index 2: "</span> <span class="cm-operator">+</span> <span class="cm-variable">value</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 设置指定索引处的元素</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">atomicArray</span>.<span class="cm-variable">set</span>(<span class="cm-number">3</span>, <span class="cm-number">10</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 原子性地将指定索引处的元素加上指定的值</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">updatedValue</span> <span class="cm-operator">=</span> <span class="cm-variable">atomicArray</span>.<span class="cm-variable">addAndGet</span>(<span class="cm-number">1</span>, <span class="cm-number">5</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Updated value at index 1: "</span> <span class="cm-operator">+</span> <span class="cm-variable">updatedValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 原子性地将指定索引处的元素递增 1</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">newValue</span> <span class="cm-operator">=</span> <span class="cm-variable">atomicArray</span>.<span class="cm-variable">incrementAndGet</span>(<span class="cm-number">4</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"New value at index 4: "</span> <span class="cm-operator">+</span> <span class="cm-variable">newValue</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 601px;"></div><div class="CodeMirror-gutters" style="display: none; height: 601px;"></div></div></div></pre><p><span>在这个示例中，我们首先创建了一个普通的整数数组 </span><code>array</code><span>，然后使用 </span><code>AtomicIntegerArray</code><span> 的构造方法将其转换为原子整数数组 </span><code>atomicArray</code><span>。</span></p><p><span>接下来，我们演示了一些常见的原子更新数组的操作：</span></p><ul><li><span>使用 </span><code>get(index)</code><span> 方法获取指定索引处的元素。</span></li><li><span>使用 </span><code>set(index, value)</code><span> 方法设置指定索引处的元素。</span></li><li><span>使用 </span><code>addAndGet(index, delta)</code><span> 方法原子性地将指定索引处的元素加上指定的增量，并返回结果。</span></li><li><span>使用 </span><code>incrementAndGet(index)</code><span> 方法原子性地将指定索引处的元素递增 1，并返回结果。</span></li></ul><p><code>AtomicIntegerArray</code><span> 还提供了其他方法，如 </span><code>getAndSet(index, value)</code><span>、</span><code>compareAndSet(index, expect, update)</code><span> 等，用于实现原子更新数组的不同操作。</span></p><p><span>使用 </span><code>AtomicIntegerArray</code><span> 可以在多线程环境下实现对数组的原子操作，避免数据竞争和不一致性的问题。它适用于需要在多个线程之间共享和更新数组数据的场景。</span></p><h3 id='113-原子更新引用类型'><span>1.1.3 原子更新引用类型</span></h3><p><span>原子更新基本类型的AtomicInteger，只能更新一个变量，如果要原子更新多个变量，就需要使用这个原子更新引用类型提供的类。Atomic包提供了以下3个类。</span>
<span>·AtomicReference：原子更新引用类型。</span>
<span>·AtomicReferenceFieldUpdater：原子更新引用类型里的字段。</span>
<span>·AtomicMarkableReference：原子更新带有标记位的引用类型。可以原子更新一个布尔类型的标记位和引用类型。构造方法是AtomicMarkableReference（V initialRef，boolean initialMark）。</span></p><h3 id='114-原子更新字段类'><span>1.1.4 原子更新字段类</span></h3><p><span>如果需原子地更新某个类里的某个字段时，就需要使用原子更新字段类，Atomic包提供</span>
<span>了以下3个类进行原子字段更新。</span>
<span>·AtomicIntegerFieldUpdater：原子更新整型的字段的更新器。</span>
<span>·AtomicLongFieldUpdater：原子更新长整型字段的更新器。</span>
<span>·AtomicStampedReference：原子更新带有版本号的引用类型。该类将整数值与引用关联起来，可用于原子的更新数据和数据的版本号，可以解决使用CAS进行原子更新时可能出现的ABA问题。</span></p><h2 id='12-java中的并发工具类'><span>1.2 Java中的并发工具类</span></h2><p><span> </span><span>在JDK的并发包里提供了几个非常有用的并发工具类。</span><strong><span>CountDownLatch、CyclicBarrier和Semaphore工具类</span></strong><span>提供了一种并发流程控制的手段，Exchanger工具类则提供了在线程间交换数据的一种手段。本章会配合一些应用场景来介绍如何使用这些工具类。</span></p><h3 id='121-等待多线程完成的countdownlatch'><span>1.2.1 等待多线程完成的CountDownLatch</span></h3><p><span> </span><strong><span>CountDownLatch允许一个或多个线程等待其他线程完成操作。</span></strong></p><p><span> </span><span>假如有这样一个需求：我们需要解析一个Excel里多个sheet的数据，此时可以考虑使用多线程，每个线程解析一个sheet里的数据，等到所有的sheet都解析完之后，程序需要提示解析完成。在这个需求中，要实现主线程等待所有线程完成sheet的解析操作，最简单的做法是使用join()方法。</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">JoinCountDownLatchTest</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) <span class="cm-keyword">throws</span> <span class="cm-variable">InterruptedException</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span> <span class="cm-variable">parser1</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-meta">@Override</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> });</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span> <span class="cm-variable">parser2</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-meta">@Override</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"parser2 finish"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> });</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">parser1</span>.<span class="cm-variable">start</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">parser2</span>.<span class="cm-variable">start</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">parser1</span>.<span class="cm-variable">join</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">parser2</span>.<span class="cm-variable">join</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"all parser finish"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 523px;"></div><div class="CodeMirror-gutters" style="display: none; height: 523px;"></div></div></div></pre><p><span> </span><span>在上面的代码中，main线程需要等待parse1与parse2线程完成之后，才能够继续进行，因为parse1与parse2都调用了join函数。</span><strong><span>join用于让当前执行线程等待join线程执行结束。其实现原理是不停检查join线程是否存活，如果join线程存活则让当前线程永远等待。其中，wait(0)表示永远等待下去。</span></strong></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">while</span> (<span class="cm-variable">isAlive</span>()) {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">wait</span>(<span class="cm-number">0</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 78px;"></div><div class="CodeMirror-gutters" style="display: none; height: 78px;"></div></div></div></pre><p><span> </span><span>直到join线程中止后，线程的this.notifyAll()方法会被调用，调用notifyAll()方法是在JVM里实现的，所以在JDK里看不到，可以查看JVM源码。</span></p><p><span> </span><strong><span>在JDK 1.5之后的并发包中提供的CountDownLatch也可以实现join的功能，并且比join的功能更多。</span></strong></p><p><span> </span><span>CountDownLatch的构造函数接收一个int类型的参数作为计数器，如果你想等待N个点完成，这里就传入N。</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">CountDownLatchTest</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 在构造CountDownLatch的时候需要传入一个整数n，在这个整数倒数到0之前，主线程需要等待在门口</span></span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 这个倒数过程是由各个执行线程驱动的，每个线程执行完任务“倒数”一次。</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// CountDownLatch()的括号里是几，表示latch.countDown()要执行几次才能唤醒主线程</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">staticCountDownLatch</span> <span class="cm-variable">c</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">CountDownLatch</span>(<span class="cm-number">2</span>); <span class="cm-comment">// 核心点1</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) <span class="cm-keyword">throws</span> <span class="cm-variable">InterruptedException</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">1</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">countDown</span>(); <span class="cm-comment">// 核心点2</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">2</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">countDown</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }).<span class="cm-variable">start</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">await</span>(); <span class="cm-comment">//核心点3</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"3"</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 501px;"></div><div class="CodeMirror-gutters" style="display: none; height: 501px;"></div></div></div></pre><p><span> </span><span>当我们调用CountDownLatch的countDown方法时，N就会减1，CountDownLatch的await方法会阻塞当前线程，直到N变成零。由于countDown方法可以用在任何地方，所以这里说的N个点，可以是N个线程，也可以是1个线程里的N个执行步骤。用在多个线程时，只需要把这个CountDownLatch的引用传递到线程里即可。</span></p><p><span>如果有某个解析sheet的线程处理得比较慢，我们不可能让主线程一直等待，所以可以使用另外一个带指定时间的await方法——await（long time，TimeUnit unit），这个方法等待特定时间后，就会不再阻塞当前线程。join也有类似的方法。</span></p><p><strong><span>注意：</span></strong></p><p><span>计数器必须大于等于0，只是等于0时候，计数器就是零，调用await方法时不会阻塞当前线程。CountDownLatch不可能重新初始化或者修改CountDownLatch对象的内部计数器的值。一个线程调用countDown方法happen-before，另外一个线程调用await方法。</span></p><h3 id='122-同步屏障'><span>1.2.2 同步屏障</span></h3><p><span> </span><span>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。</span></p><p><span> </span><span>CyclicBarrier默认的构造方法是CyclicBarrier（int parties），其参数表示屏障拦截的线程数量，每个线程调用await方法告诉CyclicBarrier我已经到达了屏障，然后当前线程被阻塞。</span></p><p><strong><span>示例代码如下：</span></strong></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" class="cm-tab-wrap-hack" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">CyclicBarrierTest</span> {<span class="cm-tab" role="presentation" cm-text=" "> </span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">staticCyclicBarrier</span> <span class="cm-variable">c</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">CyclicBarrier</span>(<span class="cm-number">2</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">1</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }).<span class="cm-variable">start</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">2</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 527px;"></div><div class="CodeMirror-gutters" style="display: none; height: 527px;"></div></div></div></pre><p><strong><span>因为主线程和子线程的调度是由CPU决定的，两个线程都有可能先执行，所以会产生两种</span></strong>
<span>输出，第一种可能输出如下。</span>
<span>1</span></p><p><span>2</span>
<span>第二种可能输出如下。</span>
<span>2</span></p><p><span>1</span></p><p><span> </span><span>如果把new CyclicBarrier(2)修改成new CyclicBarrier(3)，则主线程和子线程会永远等待，因为没有第三个线程执行await方法，即没有第三个线程到达屏障，所以之前到达屏障的两个线程都不会继续执行。</span></p><p><span> </span><span>CyclicBarrier还提供一个更高级的构造函数CyclicBarrier（int parties，Runnable barrier-Action），</span><strong><span>用于在线程到达屏障时，优先执行barrierAction，方便处理更复杂的业务场景，</span></strong></p><p><span>示例代码如下：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">CyclicBarrier</span>;</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">CyclicBarrierTest2</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">static</span> <span class="cm-variable">CyclicBarrier</span> <span class="cm-variable">c</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">CyclicBarrier</span>(<span class="cm-number">2</span>, <span class="cm-keyword">new</span> <span class="cm-variable">A</span>());</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>} <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">1</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}).<span class="cm-variable">start</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>} <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">2</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">static</span> <span class="cm-keyword">class</span> <span class="cm-def">A</span> <span class="cm-keyword">implements</span> <span class="cm-variable">Runnable</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-number">3</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 754px;"></div><div class="CodeMirror-gutters" style="display: none; height: 754px;"></div></div></div></pre><p><span> </span><span>因为CyclicBarrier设置了拦截线程的数量是2，所以必须等代码中的第一个线程和线程A都执行完之后，才会继续执行主线程，然后输出2，所以代码执行后的输出如下。</span></p><p><span>3</span></p><p><span>1</span></p><p><span>2</span></p><h4 id='1231-cyclicbarrier的应用场景'><span>1.2.3.1 CyclicBarrier的应用场景</span></h4><p><span> </span><span>CyclicBarrier可以用于多线程计算数据，最后合并计算结果的场景。例如，用一个Excel保存了用户所有银行流水，每个Sheet保存一个账户近一年的每笔银行流水，现在需要统计用户的日均银行流水，先用多线程处理每个sheet里的银行流水，都执行完之后，得到每个sheet的日均银行流水，最后，再用barrierAction用这些线程的计算结果，计算出整个Excel的日均银行流水。</span></p><p><span> </span><span>使用线程池创建4个线程，分别计算每个sheet里的数据，每个sheet计算结果是1，再由BankWaterService线程汇总4个sheet计算出的结果。</span></p><p><span>下面是一个示例代码，演示了如何使用线程池和 </span><code>CyclicBarrier</code><span> 实现对多个 Excel sheet 进行并发处理，并最终计算出整个 Excel 的日均银行流水：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">CyclicBarrier</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">ExecutorService</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">Executors</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">ExcelProcessingExample</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-keyword">final</span> <span class="cm-variable-3">int</span> <span class="cm-variable">SHEET_COUNT</span> <span class="cm-operator">=</span> <span class="cm-number">12</span>; <span class="cm-comment">// 假设有 12 个 sheet</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-keyword">final</span> <span class="cm-variable-3">int</span> <span class="cm-variable">THREAD_COUNT</span> <span class="cm-operator">=</span> <span class="cm-variable">SHEET_COUNT</span>; <span class="cm-comment">// 使用与 sheet 数量相同的线程数</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">ExecutorService</span> <span class="cm-variable">executorService</span> <span class="cm-operator">=</span> <span class="cm-variable">Executors</span>.<span class="cm-variable">newFixedThreadPool</span>(<span class="cm-variable">THREAD_COUNT</span>);</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 第二个参数是线程到达屏障的时候，执行的线程</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">CyclicBarrier</span> <span class="cm-variable">barrier</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">CyclicBarrier</span>(<span class="cm-variable">THREAD_COUNT</span>, () <span class="cm-operator">-></span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 当所有线程都到达屏障时执行的动作</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 在这里计算整个 Excel 的日均银行流水</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">double</span> <span class="cm-variable">totalAverage</span> <span class="cm-operator">=</span> <span class="cm-number">0.0</span>;</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 计算每个 sheet 的日均银行流水</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-variable">SHEET_COUNT</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 假设每个 sheet 的日均银行流水已经计算出来了，这里用随机数代替</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">double</span> <span class="cm-variable">sheetAverage</span> <span class="cm-operator">=</span> <span class="cm-variable">Math</span>.<span class="cm-variable">random</span>() <span class="cm-operator">*</span> <span class="cm-number">1000</span>;</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">printf</span>(<span class="cm-string">"Sheet %d average: %.2f%n"</span>, <span class="cm-variable">i</span> <span class="cm-operator">+</span> <span class="cm-number">1</span>, <span class="cm-variable">sheetAverage</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">totalAverage</span> <span class="cm-operator">+=</span> <span class="cm-variable">sheetAverage</span>;</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 计算整个 Excel 的日均银行流水</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">double</span> <span class="cm-variable">excelAverage</span> <span class="cm-operator">=</span> <span class="cm-variable">totalAverage</span> <span class="cm-operator">/</span> <span class="cm-variable">SHEET_COUNT</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">printf</span>(<span class="cm-string">"Excel average: %.2f%n"</span>, <span class="cm-variable">excelAverage</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">executorService</span>.<span class="cm-variable">shutdown</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> });</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 提交每个 sheet 的处理任务给线程池</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-variable">SHEET_COUNT</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">sheetNumber</span> <span class="cm-operator">=</span> <span class="cm-variable">i</span> <span class="cm-operator">+</span> <span class="cm-number">1</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">executorService</span>.<span class="cm-variable">submit</span>(() <span class="cm-operator">-></span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 假设这里是处理一个 sheet 的银行流水的逻辑</span></span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 这里使用随机数代替实际处理逻辑</span></span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">double</span> <span class="cm-variable">sheetAverage</span> <span class="cm-operator">=</span> <span class="cm-variable">Math</span>.<span class="cm-variable">random</span>() <span class="cm-operator">*</span> <span class="cm-number">1000</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">printf</span>(<span class="cm-string">"Processing Sheet %d: %.2f%n"</span>, <span class="cm-variable">sheetNumber</span>, <span class="cm-variable">sheetAverage</span>);</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-comment">// 当前线程到达屏障，等待其他线程</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">barrier</span>.<span class="cm-variable">await</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">e</span>.<span class="cm-variable">printStackTrace</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> });</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 1202px;"></div><div class="CodeMirror-gutters" style="display: none; height: 1202px;"></div></div></div></pre><p><span>在这个示例中，我们使用 </span><code>ExecutorService</code><span> 创建了一个固定大小的线程池，并设置线程数与 sheet 数量相同。</span></p><p><span>然后，我们创建了一个 </span><code>CyclicBarrier</code><span>，用于控制多个线程在到达屏障点时进行同步，并在所有线程都到达屏障时执行指定的 </span><code>barrierAction</code><span>。</span></p><p><span>通过循环提交每个 sheet 的处理任务给线程池，每个任务表示对一个 sheet 的银行流水进行处理。在每个任务的逻辑中，我们假设使用随机数代替实际的银行流水处理逻辑，并打印出每个 sheet 的平均值。</span></p><p><span>当每个任务执行完毕后，线程会调用 </span><code>barrier.await()</code><span> 方法等待其他线程，直到所有线程都到达屏障点。在屏障点后，</span><code>barrierAction</code><span> 中的计算整个 Excel 的日均银行流水的逻辑将被执行，并将线程池关闭。</span></p><p><span>注意：在实际场景中，需要根据实际的银行流水处理逻辑和 Excel 文件的结构进行适当的修改。这个示例主要展示了如何使用线程池和 </span><code>CyclicBarrier</code><span> 实现多线程并发处理，并在所有线程完成后执行特定的操作。</span></p><h4 id='1232-cyclicbarrier和countdownlatch的区别'><span>1.2.3.2 CyclicBarrier和CountDownLatch的区别</span></h4><p><span> </span><span>CountDownLatch的计数器只能使用一次，</span><strong><span>而CyclicBarrier的计数器可以使用reset()方法重置</span></strong><span>。所以CyclicBarrier能处理更为复杂的业务场景。例如，如果计算发生错误，可以重置计数器，并让线程重新执行一次。</span></p><p><span> </span><span>CyclicBarrier还提供其他有用的方法，比如getNumberWaiting方法可以获得Cyclic-Barrier阻塞的线程数量。isBroken()方法用来了解阻塞的线程是否被中断。</span></p><p><strong><span>示例代码如下：</span></strong></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">BrokenBarrierException</span>;</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">import</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">concurrent</span>.<span class="cm-variable">CyclicBarrier</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">CyclicBarrierTest3</span> {</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">static</span> <span class="cm-variable">CyclicBarrier</span> <span class="cm-variable">c</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">CyclicBarrier</span>(<span class="cm-number">2</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) <span class="cm-keyword">throws</span> <span class="cm-variable">InterruptedException，BrokenBarrierException</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">Thread</span> <span class="cm-variable">thread</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>});</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">thread</span>.<span class="cm-variable">start</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">thread</span>.<span class="cm-variable">interrupt</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">c</span>.<span class="cm-variable">await</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>} <span class="cm-keyword">catch</span> (<span class="cm-variable">Exception</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">c</span>.<span class="cm-variable">isBroken</span>()); <span class="cm-comment">//由于前面调用thread.interrupt();打断了，因此会输出true</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 625px;"></div><div class="CodeMirror-gutters" style="display: none; height: 625px;"></div></div></div></pre><h3 id='123-控制并发线程数的semaphore'><span>1.2.3 控制并发线程数的Semaphore</span></h3><p><span>Semaphore（信号量）是用来</span><strong><span>控制同时访问特定资源的线程数量，它通过协调各个线程，以保证合理的使用公共资源。</span></strong></p><h4 id='1231-应用场景'><span>1.2.3.1 应用场景</span></h4><p><span> </span><span>Semaphore可以用于做流量控制，</span><strong><span>特别是公用资源有限的应用场景，比如数据库连接。</span></strong><span>假如有一个需求，要读取几万个文件的数据，因为都是IO密集型任务，我们可以启动几十个线程并发地读取，但是如果读到内存后，还需要存储到数据库中，而数据库的连接数只有10个</span><strong><span>，这时我们必须控制只有10个线程同时获取数据库连接保存数据，否则会报错无法获取数据库连接</span></strong><span>。这个时候，就可以使用Semaphore来做流量控制。</span></p><p><strong><span>示例代码如下：</span></strong></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 11.0703px; left: 4px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">SemaphoreTest</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-keyword">final</span> <span class="cm-variable-3">int</span> <span class="cm-variable">THREAD_COUNT</span> <span class="cm-operator">=</span> <span class="cm-number">30</span>;</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-variable">ExecutorServicethreadPool</span> <span class="cm-operator">=</span> <span class="cm-variable">Executors</span>.<span class="cm-variable">newFixedThreadPool</span>(<span class="cm-variable">THREAD_COUNT</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-variable">Semaphore</span> <span class="cm-variable">s</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Semaphore</span>(<span class="cm-number">10</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span><span class="cm-operator"><</span> <span class="cm-variable">THREAD_COUNT</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">threadPool</span>.<span class="cm-variable">execute</span>(<span class="cm-keyword">new</span> <span class="cm-variable">Runnable</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span> <span class="cm-meta">@Override</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">s</span>.<span class="cm-variable">acquire</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"save data"</span>);</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">s</span>.<span class="cm-variable">release</span>();</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">catch</span> (<span class="cm-variable">InterruptedException</span> <span class="cm-variable">e</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>});</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">threadPool</span>.<span class="cm-variable">shutdown</span>(); <span class="cm-comment">// 关闭线程池，线程池具体操作在下一章进行讲解。</span></span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 571px;"></div><div class="CodeMirror-gutters" style="display: none; height: 571px;"></div></div></div></pre><p><span> </span><span>在代码中，虽然有30个线程在执行，但是只允许10个并发执行。</span><strong><span>Semaphore的构造方法Semaphore（int permits）接受一个整型的数字，表示可用的许可证数量。</span></strong></p><p><span> </span><span>Semaphore（10）表示允许10个线程获取许可证，也就是最大并发数是10。</span><strong><span>Semaphore的用法也很简单，首先线程使用Semaphore的acquire()方法获取一个许可证，使用完之后调用release()方法归还许可证</span></strong><span>。</span><strong><span>还可以用tryAcquire()方法尝试获取许可证。</span></strong></p><h4 id='1232-其他方法'><span>1.2.3.2 其他方法</span></h4><p><span>Semaphore还提供一些其他方法，具体如下。</span>
<span>·int availablePermits()：返回此信号量中当前可用的许可证数。</span>
<span>·int getQueueLength()：返回正在等待获取许可证的线程数。</span>
<span>·boolean hasQueuedThreads()：是否有线程正在等待获取许可证。</span>
<span>·void reducePermits（int reduction）：减少reduction个许可证，是个protected方法。</span>
<span>·Collection getQueuedThreads()：返回所有等待获取许可证的线程集合，是个protected方法。</span></p><h3 id='124-线程间交换数据的exchanger'><span>1.2.4 线程间交换数据的Exchanger</span></h3><p><span> </span><span>Exchanger（交换者）是一个用于线程间协作的工具类。Exchanger用于进行线程间的数据交换。它提供一个同步点，在这个同步点，两个线程可以交换彼此的数据。这两个线程通过exchange方法交换数据，</span><strong><span>如果第一个线程先执行exchange()方法，它会一直等待第二个线程也执行exchange方法，当两个线程都到达同步点时，这两个线程就可以交换数据，将本线程生产出来的数据传递给对方。</span></strong></p><h4 id='1241-应用场景'><span>1.2.4.1 应用场景</span></h4><p><span> </span><span>Exchanger可以用于遗传算法，遗传算法里需要选出两个人作为交配对象，这时候会交换两人的数据，并使用交叉规则得出2个交配结果。</span><strong><span>Exchanger也可以用于校对工作，比如我们需要将纸制银行流水通过人工的方式录入成电子银行流水，为了避免错误，采用AB岗两人进行录入，录入到Excel之后，系统需要加载这两个Excel，并对两个Excel数据进行校对，看看是否录入一致。</span></strong></p><p><span> </span><span>如果两个线程有一个没有执行exchange()方法，则会一直等待，如果担心有特殊情况发生，避免一直等待，可以使用exchange（V x，long timeout，Time Unit unit）设置最大等待时长。</span></p><h2 id='13-java中的线程池'><span>1.3 Java中的线程池</span></h2><p><span>线程池的内容不多，但是是必须掌握的。</span></p><p> </p></div></div>
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