public/signals

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      <h2><a href="./">Go by Example</a>: Signals</h2>
      
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            <p>Sometimes we&rsquo;d like our Go programs to intelligently
handle <a href="https://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>

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            <a href="https://go.dev/play/p/RKLAbvblJMQ"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="p">(</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;fmt&#34;</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;os&#34;</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;os/signal&#34;</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;syscall&#34;</span>
</span></span><span class="line"><span class="cl"><span class="p">)</span></span></span></code></pre>
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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span></span></code></pre>
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            <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. Note that this channel
should be buffered.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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></span></code></pre>
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            <p><code>signal.Notify</code> registers the given channel to
receive notifications of the specified signals.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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></span></span></code></pre>
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            <p>We could receive from <code>sigs</code> here in the main
function, but let&rsquo;s see how this could also be
done in a separate goroutine, to demonstrate
a more realistic scenario of graceful shutdown.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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></span></span></code></pre>
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            <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>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span></span></span></code></pre>
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          <pre class="chroma"><code><span class="line"><span class="cl">        <span class="nx">sig</span> <span class="o">:=</span> <span class="o">&lt;-</span><span class="nx">sigs</span>
</span></span><span class="line"><span class="cl">        <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">()</span>
</span></span><span class="line"><span class="cl">        <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></span><span class="line"><span class="cl">        <span class="nx">done</span> <span class="o">&lt;-</span> <span class="kc">true</span>
</span></span><span class="line"><span class="cl">    <span class="p">}()</span></span></span></code></pre>
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            <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>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;awaiting signal&#34;</span><span class="p">)</span>
</span></span><span class="line"><span class="cl">    <span class="o">&lt;-</span><span class="nx">done</span>
</span></span><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;exiting&#34;</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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            <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>

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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run signals.go
</span></span><span class="line"><span class="cl"><span class="go">awaiting signal
</span></span></span><span class="line"><span class="cl"><span class="go">^C
</span></span></span><span class="line"><span class="cl"><span class="go">interrupt
</span></span></span><span class="line"><span class="cl"><span class="go">exiting</span></span></span></code></pre>
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      <p class="next">
        Next example: <a href="exit">Exit</a>.
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      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>
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