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waitgroups.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: WaitGroup</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'worker-pools';
}
if (e.key == "ArrowRight") {
window.location.href = 'rate-limiting';
}
}
</script>
<body>
<div class="example" id="waitgroups">
<h2><a href="./">Go by Example 中文版</a>: WaitGroup</h2>
<table>
<tr>
<td class="docs">
<p>想要等待多个协程完成，我们可以使用 <em>wait group</em> 。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/YnBi_jvjQzm"><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>
</td>
</tr>
<tr>
<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">"time"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>每个协程都会运行该函数。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">worker</span><span class="p">(</span><span class="nx">id</span> <span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"Worker %d starting\n"</span><span class="p">,</span> <span class="nx">id</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>睡眠一秒钟，以此来模拟耗时的任务。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"Worker %d done\n"</span><span class="p">,</span> <span class="nx">id</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<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>这个 WaitGroup 用于等待这里启动的所有协程完成。
注意：如果 WaitGroup 显式传递到函数中，则应使用 <em>指针</em> 。</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>启动几个协程，并为其递增 WaitGroup 的计数器。</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">1</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><=</span> <span class="mi">5</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>避免在每个协程闭包中重复利用相同的 <code>i</code> 值
更多细节可以参考 <a href="https://golang.org/doc/faq#closures_and_goroutines">the FAQ</a></p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">i</span> <span class="o">:=</span> <span class="nx">i</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>将 worker 调用包装在一个闭包中，可以确保通知 WaitGroup 此工作线程已完成。
这样，worker 线程本身就不必知道其执行中涉及的并发原语。</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">defer</span> <span class="nx">wg</span><span class="p">.</span><span class="nf">Done</span><span class="p">()</span>
<span class="nf">worker</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
<span class="p">}()</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>阻塞，直到 WaitGroup 计数器恢复为 0；
即所有协程的工作都已经完成。</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>请注意，WaitGroup 这种使用方式没有直观的办法传递来自 worker 的错误。
更高级的用例，请参见 <a href="https://pkg.go.dev/golang.org/x/sync/errgroup">errgroup package</a></p>
</td>
<td class="code">
<pre class="chroma">
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="gp">$</span> go run waitgroups.go
<span class="go">Worker 5 starting
</span><span class="go">Worker 3 starting
</span><span class="go">Worker 4 starting
</span><span class="go">Worker 1 starting
</span><span class="go">Worker 2 starting
</span><span class="go">Worker 4 done
</span><span class="go">Worker 1 done
</span><span class="go">Worker 2 done
</span><span class="go">Worker 5 done
</span><span class="go">Worker 3 done</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>每次运行，各个协程开启和完成的时间可能是不同的。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="rate-limiting.html">速率限制</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>
<script>
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"sync\"\u000A \"time\"\u000A)\u000A');codeLines.push('func worker(id int) {\u000A fmt.Printf(\"Worker %d starting\\n\", id)\u000A');codeLines.push(' time.Sleep(time.Second)\u000A fmt.Printf(\"Worker %d done\\n\", id)\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' var wg sync.WaitGroup\u000A');codeLines.push(' for i :\u003D 1; i \u003C\u003D 5; i++ {\u000A wg.Add(1)\u000A');codeLines.push(' i :\u003D i\u000A');codeLines.push(' go func() {\u000A defer wg.Done()\u000A worker(i)\u000A }()\u000A }\u000A');codeLines.push(' wg.Wait()\u000A');codeLines.push('}\u000A');codeLines.push('');codeLines.push('');
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