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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Tickers</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'timers';
}
if (e.key == "ArrowRight") {
window.location.href = 'worker-pools';
}
}
</script>
<body>
<div class="example" id="tickers">
<h2><a href="./">Go by Example</a>: Tickers</h2>
<table>
<tr>
<td class="docs">
<p><a href="timers">Timers</a> are for when you want to do
something once in the future - <em>tickers</em> are for when
you want to do something repeatedly at regular
intervals. Here’s an example of a ticker that ticks
periodically until we stop it.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/gs6zoJP-Pl9"><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>
</td>
</tr>
<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">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Tickers use a similar mechanism to timers: a
channel that is sent values. Here we’ll use the
<code>select</code> builtin on the channel to await the
values as they arrive every 500ms.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">ticker</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nf">NewTicker</span><span class="p">(</span><span class="mi">500</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span>
<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>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">for</span> <span class="p">{</span>
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="o"><-</span><span class="nx">done</span><span class="p">:</span>
<span class="k">return</span>
<span class="k">case</span> <span class="nx">t</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">ticker</span><span class="p">.</span><span class="nx">C</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">"Tick at"</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Tickers can be stopped like timers. Once a ticker
is stopped it won’t receive any more values on its
channel. We’ll stop ours after 1600ms.</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="mi">1600</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span>
<span class="nx">ticker</span><span class="p">.</span><span class="nf">Stop</span><span class="p">()</span>
<span class="nx">done</span> <span class="o"><-</span> <span class="kc">true</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Ticker stopped"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>When we run this program the ticker should tick 3 times
before we stop it.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> go run tickers.go
<span class="go">Tick at 2012-09-23 11:29:56.487625 -0700 PDT
</span><span class="go">Tick at 2012-09-23 11:29:56.988063 -0700 PDT
</span><span class="go">Tick at 2012-09-23 11:29:57.488076 -0700 PDT
</span><span class="go">Ticker stopped</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="worker-pools">Worker Pools</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>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"time\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' ticker :\u003D time.NewTicker(500 * time.Millisecond)\u000A done :\u003D make(chan bool)\u000A');codeLines.push(' go func() {\u000A for {\u000A select {\u000A case \u003C-done:\u000A return\u000A case t :\u003D \u003C-ticker.C:\u000A fmt.Println(\"Tick at\", t)\u000A }\u000A }\u000A }()\u000A');codeLines.push(' time.Sleep(1600 * time.Millisecond)\u000A ticker.Stop()\u000A done \u003C- true\u000A fmt.Println(\"Ticker stopped\")\u000A}\u000A');codeLines.push('');
</script>
<script src="site.js" async></script>
</body>
</html>