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signals
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Signals</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'execing-processes';
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<body>
<div class="example" id="signals">
<h2><a href="./">Go by Example</a>: Signals</h2>
<table>
<tr>
<td class="docs">
<p>Sometimes we’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’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/LauPuRo3v9l"><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">"os"</span>
<span class="s">"os/signal"</span>
<span class="s">"syscall"</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>Go signal notification works by sending <code>os.Signal</code>
values on a channel. We’ll create a channel to
receive these notifications. Note that this channel
should be buffered.</p>
</td>
<td class="code leading">
<pre class="chroma">
<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>
</pre>
</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">
<pre class="chroma">
<span class="nx">signal</span><span class="p">.</span><span class="nf">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>
</td>
</tr>
<tr>
<td class="docs">
<p>We could receive from <code>sigs</code> here in the main
function, but let’s see how this could also be
done in a separate goroutine, to demonstrate
a more realistic scenario of graceful shutdown.</p>
</td>
<td class="code leading">
<pre class="chroma">
<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>
</td>
</tr>
<tr>
<td class="docs">
<p>This goroutine executes a blocking receive for
signals. When it gets one it’ll print it out
and then notify the program that it can finish.</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>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">sig</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">sigs</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</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">sig</span><span class="p">)</span>
<span class="nx">done</span> <span class="o"><-</span> <span class="kc">true</span>
<span class="p">}()</span>
</pre>
</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">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"awaiting signal"</span><span class="p">)</span>
<span class="o"><-</span><span class="nx">done</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"exiting"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</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">
<pre class="chroma">
<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>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="exit">Exit</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
<script>
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"os\"\u000A \"os/signal\"\u000A \"syscall\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' sigs :\u003D make(chan os.Signal, 1)\u000A');codeLines.push(' signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)\u000A');codeLines.push(' done :\u003D make(chan bool, 1)\u000A');codeLines.push(' go func() {\u000A');codeLines.push(' sig :\u003D \u003C-sigs\u000A fmt.Println()\u000A fmt.Println(sig)\u000A done \u003C- true\u000A }()\u000A');codeLines.push(' fmt.Println(\"awaiting signal\")\u000A \u003C-done\u000A fmt.Println(\"exiting\")\u000A}\u000A');codeLines.push('');
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</body>
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