timers

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    <div class="example" id="timers">
      <h2><a href="./">Go by Example</a>: Timers</h2>

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            <p>We often want to execute Go code at some point in the
future, or repeatedly at some interval. Go&rsquo;s built-in
<em>timer</em> and <em>ticker</em> features make both of these tasks
easy. We&rsquo;ll look first at timers and then
at <a href="tickers">tickers</a>.</p>

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	        <a href="http://play.golang.org/p/6fSHrYxpMu"><img title="Run code" src="play.png" class="run" /></a>
            <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>

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            <div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;time&quot;</span>
<span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
</pre></div>

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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>
</pre></div>

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            <p>Timers represent a single event in the future. You
tell the timer how long you want to wait, and it
provides a channel that will be notified at that
time. This timer will wait 2 seconds.</p>

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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="nx">time</span><span class="p">.</span><span class="nx">Second</span> <span class="o">*</span> <span class="mi">2</span><span class="p">)</span>
</pre></div>

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            <p>The <code>&lt;-timer1.C</code> blocks on the timer&rsquo;s channel <code>C</code>
until it sends a value indicating that the timer
expired.</p>

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            <div class="highlight"><pre>    <span class="o">&lt;-</span><span class="nx">timer1</span><span class="p">.</span><span class="nx">C</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Timer 1 expired&quot;</span><span class="p">)</span>
</pre></div>

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            <p>If you just wanted to wait, you could have used
<code>time.Sleep</code>. One reason a timer may be useful is
that you can cancel the timer before it expires.
Here&rsquo;s an example of that.</p>

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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>
    <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
        <span class="o">&lt;-</span><span class="nx">timer2</span><span class="p">.</span><span class="nx">C</span>
        <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Timer 2 expired&quot;</span><span class="p">)</span>
    <span class="p">}()</span>
    <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>
    <span class="k">if</span> <span class="nx">stop2</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;Timer 2 stopped&quot;</span><span class="p">)</span>
    <span class="p">}</span>
<span class="p">}</span>
</pre></div>

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            <p>The first timer will expire ~2s after we start the
program, but the second should be stopped before it has
a chance to expire.</p>

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            <div class="highlight"><pre><span class="gp">$</span> go run timers.go
<span class="go">Timer 1 expired</span>
<span class="go">Timer 2 stopped</span>
</pre></div>

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      <p class="next">
        Next example: <a href="tickers">Tickers</a>.
      </p>

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        by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</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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