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atomic-counters.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 原子计数器</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
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<body>
<div class="example" id="atomic-counters">
<h2><a href="./">Go by Example 中文版</a>: 原子计数器</h2>
<table>
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<td class="docs">
<p>Go 中最主要的状态管理机制是依靠通道间的通信来完成的。
我们已经在<a href="worker-pools">工作池</a>的例子中看到过，并且，还有一些其他的方法来管理状态。
这里，我们来看看如何使用 <code>sync/atomic</code> 包在多个协程中进行 _原子计数_。</p>
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<td class="code empty leading">
</td>
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<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/ms0i-0FMWVt"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
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<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"sync"</span>
<span class="s">"sync/atomic"</span>
<span class="p">)</span>
</pre>
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<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们将使用一个无符号整型（永远是正整数）变量来表示这个计数器。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">var</span> <span class="nx">ops</span> <span class="kt">uint64</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>WaitGroup 帮助我们等待所有协程完成它们的工作。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">var</span> <span class="nx">wg</span> <span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们会启动 50 个协程，并且每个协程会将计数器递增 1000 次。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="mi">50</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">wg</span><span class="p">.</span><span class="nf">Add</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>使用 <code>AddUint64</code> 来让计数器自动增加，
使用 <code>&</code> 语法给定 <code>ops</code> 的内存地址。</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">for</span> <span class="nx">c</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">c</span> <span class="p"><</span> <span class="mi">1000</span><span class="p">;</span> <span class="nx">c</span><span class="o">++</span> <span class="p">{</span>
</pre>
</td>
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<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">atomic</span><span class="p">.</span><span class="nf">AddUint64</span><span class="p">(</span><span class="o">&</span><span class="nx">ops</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="p">}</span>
<span class="nx">wg</span><span class="p">.</span><span class="nf">Done</span><span class="p">()</span>
<span class="p">}()</span>
<span class="p">}</span>
</pre>
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<tr>
<td class="docs">
<p>等待，直到所有协程完成。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">wg</span><span class="p">.</span><span class="nf">Wait</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>现在可以安全的访问 <code>ops</code>，因为我们知道，此时没有协程写入 <code>ops</code>，
此外，还可以使用 <code>atomic.LoadUint64</code> 之类的函数，在原子更新的同时安全地读取它们。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"ops:"</span><span class="p">,</span> <span class="nx">ops</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>预计会进行 50,000 次操作。如果我们使用非原子的 <code>ops++</code> 来增加计数器，
由于多个协程会互相干扰，运行时值会改变，可能会导致我们得到一个不同的数字。
此外，运行程序时带上 <code>-race</code> 标志，我们可以获取数据竞争失败的详情。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go run atomic-counters.go
<span class="go">ops: 50000</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>接下来，我们看一下管理状态的另一个工具——互斥锁。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="mutexes">互斥锁</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
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