175 lines
7.4 KiB
Plaintext
175 lines
7.4 KiB
Plaintext
<!DOCTYPE html>
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<html>
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<meta charset="utf-8">
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<title>Go by Example: Signals</title>
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<link rel=stylesheet href="site.css">
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</head>
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<body>
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<div class="example" id="signals">
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<h2><a href="./">Go by Example</a>: Signals</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Sometimes we’d like our Go programs to intelligently
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handle <a href="http://en.wikipedia.org/wiki/Unix_signal">Unix signals</a>.
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For example, we might want a server to gracefully
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shutdown when it receives a <code>SIGTERM</code>, or a command-line
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tool to stop processing input if it receives a <code>SIGINT</code>.
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Here’s how to handle signals in Go with channels.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/9koJAW1raI5"><img title="Run code" class="run" src="data:image/png;base64,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" /></a>
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span>
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<span class="kn">import</span> <span class="s">"os"</span>
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<span class="kn">import</span> <span class="s">"os/signal"</span>
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<span class="kn">import</span> <span class="s">"syscall"</span>
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</pre></div>
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</td>
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<td class="docs">
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Go signal notification works by sending <code>os.Signal</code>
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values on a channel. We’ll create a channel to
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receive these notifications (we’ll also make one to
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notify us when the program can exit).</p>
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</td>
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<td class="code leading">
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<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>
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<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>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p><code>signal.Notify</code> registers the given channel to
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receive notifications of the specified signals.</p>
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</td>
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<td class="code leading">
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<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>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>This goroutine executes a blocking receive for
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signals. When it gets one it’ll print it out
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and then notify the program that it can finish.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">sig</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">sigs</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">()</span>
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<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>
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<span class="nx">done</span> <span class="o"><-</span> <span class="kc">true</span>
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<span class="p">}()</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The program will wait here until it gets the
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expected signal (as indicated by the goroutine
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above sending a value on <code>done</code>) and then exit.</p>
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</td>
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<td class="code">
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<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">"awaiting signal"</span><span class="p">)</span>
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<span class="o"><-</span><span class="nx">done</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"exiting"</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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<p>When we run this program it will block waiting for a
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signal. By typing <code>ctrl-C</code> (which the
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terminal shows as <code>^C</code>) we can send a <code>SIGINT</code> signal,
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causing the program to print <code>interrupt</code> and then exit.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run signals.go
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<span class="go">awaiting signal</span>
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<span class="go">^C</span>
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<span class="go">interrupt</span>
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<span class="go">exiting</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="exit">Exit</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/signals">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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</div>
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</body>
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</html>
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