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channel-synchronization
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channel-synchronization
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Channel Synchronization</title>
<link rel=stylesheet href="site.css">
</head>
<script>
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<div class="example" id="channel-synchronization">
<h2><a href="./">Go by Example</a>: Channel Synchronization</h2>
<table>
<tr>
<td class="docs">
<p>We can use channels to synchronize execution
across goroutines. Here’s an example of using a
blocking receive to wait for a goroutine to finish.
When waiting for multiple goroutines to finish,
you may prefer to use a <a href="waitgroups">WaitGroup</a>.</p>
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<a href="https://go.dev/play/p/Nw-1DzIGk5f"><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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<td class="docs">
</td>
<td class="code leading">
<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">"fmt"</span>
</span></span><span class="line"><span class="cl"> <span class="s">"time"</span>
</span></span><span class="line"><span class="cl"><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>This is the function we’ll run in a goroutine. The
<code>done</code> channel will be used to notify another
goroutine that this function’s work is done.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">worker</span><span class="p">(</span><span class="nx">done</span> <span class="kd">chan</span> <span class="kt">bool</span><span class="p">)</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">Print</span><span class="p">(</span><span class="s">"working..."</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</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="s">"done"</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>Send a value to notify that we’re done.</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="kc">true</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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<td class="docs">
</td>
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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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<td class="docs">
<p>Start a worker goroutine, giving it the channel to
notify on.</p>
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<td class="code leading">
<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><span class="line"><span class="cl"> <span class="k">go</span> <span class="nf">worker</span><span class="p">(</span><span class="nx">done</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>Block until we receive a notification from the
worker on the channel.</p>
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<td class="code">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="o"><-</span><span class="nx">done</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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<td class="docs">
</td>
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run channel-synchronization.go
</span></span><span class="line"><span class="cl"><span class="go">working...done </span></span></span></code></pre>
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<td class="docs">
<p>If you removed the <code><- done</code> line from this program, the
program would exit before the <code>worker</code> even
started.</p>
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<td class="code empty">
</td>
</tr>
</table>
<p class="next">
Next example: <a href="channel-directions">Channel Directions</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 \"time\"\u000A)\u000A');codeLines.push('func worker(done chan bool) {\u000A fmt.Print(\"working...\")\u000A time.Sleep(time.Second)\u000A fmt.Println(\"done\")\u000A');codeLines.push(' done \u003C- true\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' done :\u003D make(chan bool, 1)\u000A go worker(done)\u000A');codeLines.push(' \u003C-done\u000A}\u000A');codeLines.push('');codeLines.push('');
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