baf22e84e7
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159 lines
6.6 KiB
Plaintext
159 lines
6.6 KiB
Plaintext
<!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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<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/pybl9hRvJq2">
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<img title="Run code" class="run" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAPCAYAAADtc08vAAAABGdBTUEAANbY1E9YMgAAABl0RVh0U29mdHdhcmUAQWRvYmUgSW1hZ2VSZWFkeXHJZTwAAAJ1SURBVCjPY/j//z8DMu7o6GAAgpQgD9tLqcmJH4KDg14aaik/MtdXe2ZjY6OCrh6Fs2jRYmZ9Pd05M9uL/u9dPfU/CLS0dfxvKIz/X5Dg/z8pKdkGqwGpqakMUdExDHJSYqt37tjxf+qUSf9rc2P+79298/+RA3v+H1zV///o6r7/DrbWFQkJiQwxMTGoBjAxMTpKiQmuqMuP/f/xw/v/J0+f/W9tbvTfxVLn/8rJVf+v757z/96hRf8TQtxuCQmLMjk4OKAawMfDVWVvrvd85eTq/7tXTP6/e/XM/22lif9LCnL+b13Q/v/Kzln/L++c/X/7/Jb/VpYWuZFRUagGAAErEBtlxvi+vn944f9L26cDNcz6v21R9/8zm6aC2SBDbu+f/78kK+4/L79AO7oBYCAqxD/57JZp/y/tmPX/wrYZ/6+CbAayD6zs/78daBjIgPayFJAGG6wGAIFAcpjH/dv7F4ANABuya/b/Od3l/ye2V/+/tnv2/7ldxSANmrgMYGBhZg7fuagD7GyYIeeBrrqwdRrQgLn/l02sBGkwwWkAEAjV5EZ/vQV0LswAGAYZsLC3DKTBAJ8BzCkRni/uHFyIYcAtoNc6ypL/ANVIohigrKwMxqqqqgxMzKzM6VHeL+6iGQAKzDtAV5XlJv3n5uFLRTHgzZs3YPzz50+GwqJiPitD9Y8Pjy4BB+CNvfP+3wUmIpAhhckhr3X19LodHZ28UQxQU1MDYw0NDQYBAQEeoBOTK7JjP2xf3Pt/bkfB/4KkoDcKMmIL5OXlFerq6hhu3rzJgC8MwMDYxGSfm5vbVn9/f0cgVxAkpqioyFBfX49iAACbTAK+xT3CzgAAAABJRU5ErkJggg==" />
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</a>
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"time"</span>
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<span class="kn">import</span> <span class="s">"fmt"</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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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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<div class="highlight"><pre> <span class="nx">timer1</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">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></div>
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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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expired.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <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="nx">Println</span><span class="p">(</span><span class="s">"Timer 1 expired"</span><span class="p">)</span>
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</pre></div>
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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 expires.
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Here’s an example of that.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">timer2</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">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="nx">Println</span><span class="p">(</span><span class="s">"Timer 2 expired"</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="nx">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="nx">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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<span class="p">}</span>
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</pre></div>
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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 expire ~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 expire.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run timers.go
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<span class="go">Timer 1 expired</span>
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<span class="go">Timer 2 stopped</span>
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</pre></div>
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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> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/timers">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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</body>
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</html>
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