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goroutines
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Goroutines</title>
<link rel=stylesheet href="site.css">
</head>
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<body>
<div class="example" id="goroutines">
<h2><a href="./">Go by Example</a>: Goroutines</h2>
<table>
<tr>
<td class="docs">
<p>A <em>goroutine</em> is a lightweight thread of execution.</p>
</td>
<td class="code empty leading">
</td>
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<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/I7scqRijEJt"><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>
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<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">"time"</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">f</span><span class="p">(</span><span class="nx">from</span> <span class="kt">string</span><span class="p">)</span> <span class="p">{</span>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</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">from</span><span class="p">,</span> <span class="s">":"</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
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<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>Suppose we have a function call <code>f(s)</code>. Here’s how
we’d call that in the usual way, running it
synchronously.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nf">f</span><span class="p">(</span><span class="s">"direct"</span><span class="p">)</span>
</pre>
</td>
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<tr>
<td class="docs">
<p>To invoke this function in a goroutine, use
<code>go f(s)</code>. This new goroutine will execute
concurrently with the calling one.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">go</span> <span class="nf">f</span><span class="p">(</span><span class="s">"goroutine"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You can also start a goroutine for an anonymous
function call.</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="nx">msg</span> <span class="kt">string</span><span class="p">)</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">msg</span><span class="p">)</span>
<span class="p">}(</span><span class="s">"going"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Our two function calls are running asynchronously in
separate goroutines now. Wait for them to finish
(for a more robust approach, use a <a href="waitgroups">WaitGroup</a>).</p>
</td>
<td class="code">
<pre class="chroma">
<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 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 class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>When we run this program, we see the output of the
blocking call first, then the output of the two
goroutines. The goroutines’ output may be interleaved,
because goroutines are being run concurrently by the
Go runtime.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go run goroutines.go
<span class="go">direct : 0
</span><span class="go">direct : 1
</span><span class="go">direct : 2
</span><span class="go">goroutine : 0
</span><span class="go">going
</span><span class="go">goroutine : 1
</span><span class="go">goroutine : 2
</span><span class="go">done</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Next we’ll look at a complement to goroutines in
concurrent Go programs: channels.</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
Next example: <a href="channels">Channels</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>
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