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timeouts.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 超时处理</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'select';
}
if (e.key == "ArrowRight") {
window.location.href = 'non-blocking-channel-operations';
}
}
</script>
<body>
<div class="example" id="timeouts">
<h2><a href="./">Go by Example 中文版</a>: 超时处理</h2>
<table>
<tr>
<td class="docs">
<p><em>超时</em> 对于一个需要连接外部资源，
或者有耗时较长的操作的程序而言是很重要的。
得益于通道和 <code>select</code>，在 Go 中实现超时操作是简洁而优雅的。</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/cobR8WBwrjt"><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">"time"</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>在这个例子中，假如我们执行一个外部调用，
并在 2 秒后使用通道 <code>c1</code> 返回它的执行结果。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">c1</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">string</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">c1</span> <span class="o"><-</span> <span class="s">"result 1"</span>
<span class="p">}()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这里是使用 <code>select</code> 实现一个超时操作。
<code>res := <- c1</code> 等待结果，<code><-time.After</code> 等待超时（1秒钟）以后发送的值。
由于 <code>select</code> 默认处理第一个已准备好的接收操作，
因此如果操作耗时超过了允许的 1 秒的话，将会执行超时 case。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c1</span><span class="p">:</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">res</span><span class="p">)</span>
<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nf">After</span><span class="p">(</span><span class="mi">1</span> <span class="o">*</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">Println</span><span class="p">(</span><span class="s">"timeout 1"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>如果我们允许一个长一点的超时时间：3 秒，
就可以成功的从 <code>c2</code> 接收到值，并且打印出结果。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">c2</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">string</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">c2</span> <span class="o"><-</span> <span class="s">"result 2"</span>
<span class="p">}()</span>
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c2</span><span class="p">:</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">res</span><span class="p">)</span>
<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nf">After</span><span class="p">(</span><span class="mi">3</span> <span class="o">*</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">Println</span><span class="p">(</span><span class="s">"timeout 2"</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>运行这个程序，首先显示运行超时的操作，然后是成功接收的。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> go run timeouts.go
<span class="go">timeout 1
</span><span class="go">result 2</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="non-blocking-channel-operations">非阻塞通道操作</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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