public/goroutines

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    <title>Go by Example: Goroutines</title>
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    <div class="example" id="goroutines">
      <h2><a href="./">Go by Example</a>: Goroutines</h2>
      
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            <p>A <em>goroutine</em> is a lightweight thread of execution.</p>

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            <a href="https://go.dev/play/p/I7scqRijEJt"><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;time&#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">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></span><span class="line"><span class="cl">    <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">&lt;</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</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">from</span><span class="p">,</span> <span class="s">&#34;:&#34;</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
</span></span><span class="line"><span class="cl">    <span class="p">}</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>Suppose we have a function call <code>f(s)</code>. Here&rsquo;s how
we&rsquo;d call that in the usual way, running it
synchronously.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nf">f</span><span class="p">(</span><span class="s">&#34;direct&#34;</span><span class="p">)</span></span></span></code></pre>
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            <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>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="k">go</span> <span class="nf">f</span><span class="p">(</span><span class="s">&#34;goroutine&#34;</span><span class="p">)</span></span></span></code></pre>
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            <p>You can also start a goroutine for an anonymous
function call.</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="nx">msg</span> <span class="kt">string</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">Println</span><span class="p">(</span><span class="nx">msg</span><span class="p">)</span>
</span></span><span class="line"><span class="cl">    <span class="p">}(</span><span class="s">&#34;going&#34;</span><span class="p">)</span></span></span></code></pre>
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            <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>

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          <pre class="chroma"><code><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">&#34;done&#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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          <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&rsquo; output may be interleaved,
because goroutines are being run concurrently by the
Go runtime.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run goroutines.go
</span></span><span class="line"><span class="cl"><span class="go">direct : 0
</span></span></span><span class="line"><span class="cl"><span class="go">direct : 1
</span></span></span><span class="line"><span class="cl"><span class="go">direct : 2
</span></span></span><span class="line"><span class="cl"><span class="go">goroutine : 0
</span></span></span><span class="line"><span class="cl"><span class="go">going
</span></span></span><span class="line"><span class="cl"><span class="go">goroutine : 1
</span></span></span><span class="line"><span class="cl"><span class="go">goroutine : 2
</span></span></span><span class="line"><span class="cl"><span class="go">done</span></span></span></code></pre>
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            <p>Next we&rsquo;ll look at a complement to goroutines in
concurrent Go programs: channels.</p>

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      <p class="next">
        Next example: <a href="channels">Channels</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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