/gobyexample

Permalink
Find file
gobyexample/public/signals
Fetching contributors…
Cannot retrieve contributors at this time
Raw Blame History
187 lines (144 sloc) 7.04 KB
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Signals</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="signals">
<h2><a href="./">Go by Example</a>: Signals</h2>
<table>
<tr>
<td class="docs">
<p>Sometimes we&rsquo;d like our Go programs to intelligently
handle <a href="http://en.wikipedia.org/wiki/Unix_signal">Unix signals</a>.
For example, we might want a server to gracefully
shutdown when it receives a <code>SIGTERM</code>, or a command-line
tool to stop processing input if it receives a <code>SIGINT</code>.
Here&rsquo;s how to handle signals in Go with channels.</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/BlkqAtKsxo"><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">&quot;fmt&quot;</span>
<span class="kn">import</span> <span class="s">&quot;os&quot;</span>
<span class="kn">import</span> <span class="s">&quot;os/signal&quot;</span>
<span class="kn">import</span> <span class="s">&quot;syscall&quot;</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>Go signal notification works by sending <code>os.Signal</code>
values on a channel. We&rsquo;ll create a channel to
receive these notifications (we&rsquo;ll also make one to
notify us when the program can exit).</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">sigs</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Signal</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="nx">done</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">bool</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>signal.Notify</code> registers the given channel to
receive notifications of the specified signals.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">signal</span><span class="p">.</span><span class="nx">Notify</span><span class="p">(</span><span class="nx">sigs</span><span class="p">,</span> <span class="nx">syscall</span><span class="p">.</span><span class="nx">SIGINT</span><span class="p">,</span> <span class="nx">syscall</span><span class="p">.</span><span class="nx">SIGTERM</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>This goroutine executes a blocking receive for
signals. When it gets one it&rsquo;ll print it out
and then notify the program that it can finish.</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">sig</span> <span class="o">:=</span> <span class="o">&lt;-</span><span class="nx">sigs</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</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="nx">sig</span><span class="p">)</span>
<span class="nx">done</span> <span class="o">&lt;-</span> <span class="kc">true</span>
<span class="p">}()</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>The program will wait here until it gets the
expected signal (as indicated by the goroutine
above sending a value on <code>done</code>) and then exit.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;awaiting signal&quot;</span><span class="p">)</span>
<span class="o">&lt;-</span><span class="nx">done</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;exiting&quot;</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>When we run this program it will block waiting for a
signal. By typing <code>ctrl-C</code> (which the
terminal shows as <code>^C</code>) we can send a <code>SIGINT</code> signal,
causing the program to print <code>interrupt</code> and then exit.</p>
</td>
<td class="code">
<div class="highlight"><pre><span class="gp">$</span> go run signals.go
<span class="go">awaiting signal</span>
<span class="go">^C</span>
<span class="go">interrupt</span>
<span class="go">exiting</span>
</pre></div>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="exit">Exit</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/signals">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
</body>
</html>