190 lines
7.2 KiB
Plaintext
Generated
190 lines
7.2 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Timers</title>
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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'range-over-channels';
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if (e.key == "ArrowRight") {
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window.location.href = 'tickers';
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<body>
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<div class="example" id="timers">
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<h2><a href="./">Go by Example</a>: Timers</h2>
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<table>
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<tr>
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<td class="docs">
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<p>We often want to execute Go code at some point in the
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future, or repeatedly at some interval. Go’s built-in
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<em>timer</em> and <em>ticker</em> features make both of these tasks
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easy. We’ll look first at timers and then
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at <a href="tickers">tickers</a>.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/gF7VLRz3URM"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"time"</span>
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<span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Timers represent a single event in the future. You
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tell the timer how long you want to wait, and it
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provides a channel that will be notified at that
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time. This timer will wait 2 seconds.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">timer1</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nf">NewTimer</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The <code><-timer1.C</code> blocks on the timer’s channel <code>C</code>
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until it sends a value indicating that the timer
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fired.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="o"><-</span><span class="nx">timer1</span><span class="p">.</span><span class="nx">C</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Timer 1 fired"</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>If you just wanted to wait, you could have used
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<code>time.Sleep</code>. One reason a timer may be useful is
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that you can cancel the timer before it fires.
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Here’s an example of that.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">timer2</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nf">NewTimer</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
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<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
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<span class="o"><-</span><span class="nx">timer2</span><span class="p">.</span><span class="nx">C</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Timer 2 fired"</span><span class="p">)</span>
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<span class="p">}()</span>
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<span class="nx">stop2</span> <span class="o">:=</span> <span class="nx">timer2</span><span class="p">.</span><span class="nf">Stop</span><span class="p">()</span>
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<span class="k">if</span> <span class="nx">stop2</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Timer 2 stopped"</span><span class="p">)</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Give the <code>timer2</code> enough time to fire, if it ever
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was going to, to show it is in fact stopped.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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<p>The first timer will fire ~2s after we start the
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program, but the second should be stopped before it has
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a chance to fire.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<span class="gp">$</span> go run timers.go
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<span class="go">Timer 1 fired
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</span><span class="go">Timer 2 stopped</span></pre>
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="tickers">Tickers</a>.
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</p>
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<p class="footer">
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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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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"time\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' timer1 :\u003D time.NewTimer(2 * time.Second)\u000A');codeLines.push(' \u003C-timer1.C\u000A fmt.Println(\"Timer 1 fired\")\u000A');codeLines.push(' timer2 :\u003D time.NewTimer(time.Second)\u000A go func() {\u000A \u003C-timer2.C\u000A fmt.Println(\"Timer 2 fired\")\u000A }()\u000A stop2 :\u003D timer2.Stop()\u000A if stop2 {\u000A fmt.Println(\"Timer 2 stopped\")\u000A }\u000A');codeLines.push(' time.Sleep(2 * time.Second)\u000A}\u000A');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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