182 lines
7.1 KiB
Plaintext
182 lines
7.1 KiB
Plaintext
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta http-eqiv="content-type" content="text/html;charset=utf-8">
|
|
<title>Go by Example: Select</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script type="text/javascript">
|
|
if (window.location.host == "gobyexample.com") {
|
|
var _gaq = _gaq || [];
|
|
_gaq.push(['_setAccount', 'UA-34996217-1']);
|
|
_gaq.push(['_trackPageview']);
|
|
(function() {
|
|
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
|
|
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
|
|
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
|
|
})();
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="select">
|
|
<h2><a href="./">Go by Example</a>: Select</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Go’s <em>select</em> lets you wait on multiple channel
|
|
operations. Combining goroutines and channels with
|
|
select is a powerful feature of Go.</p>
|
|
|
|
</td>
|
|
<td class="code empty leading">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
<a href="http://play.golang.org/p/Vco7d8Lmhn"><img title="Run code" src="play.png" class="run" /></a>
|
|
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="kn">import</span> <span class="s">"time"</span>
|
|
<span class="kn">import</span> <span class="s">"fmt"</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>For our example we’ll select across two channels.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <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="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>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Each channel will receive a value after some amount
|
|
of time, to simulate e.g. blocking RPC operations
|
|
executing in concurrent goroutines.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <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="nx">Sleep</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span> <span class="o">*</span> <span class="mi">1</span><span class="p">)</span>
|
|
<span class="nx">c1</span> <span class="o"><-</span> <span class="s">"one"</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="nx">Sleep</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span> <span class="o">*</span> <span class="mi">2</span><span class="p">)</span>
|
|
<span class="nx">c2</span> <span class="o"><-</span> <span class="s">"two"</span>
|
|
<span class="p">}()</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>We’ll use <code>select</code> to await both of these values
|
|
simultaneously, printing each one as it arrives.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<div class="highlight"><pre> <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">2</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
|
|
<span class="k">select</span> <span class="p">{</span>
|
|
<span class="k">case</span> <span class="nx">msg1</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="nx">Println</span><span class="p">(</span><span class="s">"received"</span><span class="p">,</span> <span class="nx">msg1</span><span class="p">)</span>
|
|
<span class="k">case</span> <span class="nx">msg2</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="nx">Println</span><span class="p">(</span><span class="s">"received"</span><span class="p">,</span> <span class="nx">msg2</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>We receive the values <code>"one"</code> and then <code>"two"</code> as
|
|
expected.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="gp">$</span> <span class="nb">time </span>go run <span class="k">select</span>.go
|
|
<span class="go">received one</span>
|
|
<span class="go">received two</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Note that the total execution time is only ~2 seconds
|
|
since both the 1 and 2 second <code>Sleeps</code> execute
|
|
concurrently.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<div class="highlight"><pre><span class="go">real 0m2.245s</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
|
|
<p class="next">
|
|
Next example: <a href="timeouts">Timeouts</a>.
|
|
</p>
|
|
|
|
<p class="footer">
|
|
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/select">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
|
|
</p>
|
|
</div>
|
|
</body>
|
|
</html>
|