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gobyexample/public/goroutines
Hana 9e216da9ef go.mod: add go.mod and move pygments to third_party 
After go1.16, go will use module mode by default,
even when the repository is checked out under GOPATH
or in a one-off directory. Add go.mod, go.sum to keep
this repo buildable without opting out of the module
mode.

> go mod init github.com/mmcgrana/gobyexample
> go mod tidy
> go mod vendor

In module mode, the 'vendor' directory is special
and its contents will be actively maintained by the
go command. pygments aren't the dependency the go will
know about, so it will delete the contents from vendor
directory. Move it to `third_party` directory now.

And, vendor the blackfriday package.

Note: the tutorial contents are not affected by the
change in go1.16 because all the examples in this
tutorial ask users to run the go command with the
explicit list of files to be compiled (e.g.
`go run hello-world.go` or `go build command-line-arguments.go`).
When the source list is provided, the go command does
not have to compute the build list and whether it's
running in GOPATH mode or module mode becomes irrelevant.
2021-02-15 16:45:26 -05:00

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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>
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<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>
<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" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;time&quot;</span>
<span class="p">)</span>
</pre></div>
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</tr>
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<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">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">&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 class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">from</span><span class="p">,</span> <span class="s">&quot;:&quot;</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<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>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">f</span><span class="p">(</span><span class="s">&quot;direct&quot;</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<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">
<div class="highlight"><pre> <span class="k">go</span> <span class="nx">f</span><span class="p">(</span><span class="s">&quot;goroutine&quot;</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>You can also start a goroutine for an anonymous
function call.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <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="nx">Println</span><span class="p">(</span><span class="nx">msg</span><span class="p">)</span>
<span class="p">}(</span><span class="s">&quot;going&quot;</span><span class="p">)</span>
</pre></div>
</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">
<div class="highlight"><pre> <span class="nx">time</span><span class="p">.</span><span class="nx">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="nx">Println</span><span class="p">(</span><span class="s">&quot;done&quot;</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</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 interleaved output of the
two goroutines. This interleaving reflects the
goroutines being run concurrently by the Go runtime.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><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></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Next we&rsquo;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> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/goroutines">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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