228 lines
10 KiB
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228 lines
10 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: Worker Pools</title>
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<div class="example" id="worker-pools">
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<h2><a href="./">Go by Example</a>: Worker Pools</h2>
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<table>
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<tr>
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<td class="docs">
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<p>In this example we’ll look at how to implement
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a <em>worker pool</em> using goroutines and channels.</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/hiSJJsYZJKL"><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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<p>Here’s the worker, of which we’ll run several
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concurrent instances. These workers will receive
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work on the <code>jobs</code> channel and send the corresponding
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results on <code>results</code>. We’ll sleep a second per job to
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simulate an expensive task.</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="kd">func</span> <span class="nf">worker</span><span class="p">(</span><span class="nx">id</span> <span class="kt">int</span><span class="p">,</span> <span class="nx">jobs</span> <span class="o"><-</span><span class="kd">chan</span> <span class="kt">int</span><span class="p">,</span> <span class="nx">results</span> <span class="kd">chan</span><span class="o"><-</span> <span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">jobs</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">"worker"</span><span class="p">,</span> <span class="nx">id</span><span class="p">,</span> <span class="s">"started job"</span><span class="p">,</span> <span class="nx">j</span><span class="p">)</span>
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<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</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="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"worker"</span><span class="p">,</span> <span class="nx">id</span><span class="p">,</span> <span class="s">"finished job"</span><span class="p">,</span> <span class="nx">j</span><span class="p">)</span>
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<span class="nx">results</span> <span class="o"><-</span> <span class="nx">j</span> <span class="o">*</span> <span class="mi">2</span>
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<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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</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>In order to use our pool of workers we need to send
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them work and collect their results. We make 2
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channels for this.</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="kd">const</span> <span class="nx">numJobs</span> <span class="p">=</span> <span class="mi">5</span>
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<span class="nx">jobs</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">int</span><span class="p">,</span> <span class="nx">numJobs</span><span class="p">)</span>
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<span class="nx">results</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">int</span><span class="p">,</span> <span class="nx">numJobs</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>This starts up 3 workers, initially blocked
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because there are no jobs yet.</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="k">for</span> <span class="nx">w</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">w</span> <span class="o"><=</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">w</span><span class="o">++</span> <span class="p">{</span>
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<span class="k">go</span> <span class="nf">worker</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span> <span class="nx">jobs</span><span class="p">,</span> <span class="nx">results</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>Here we send 5 <code>jobs</code> and then <code>close</code> that
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channel to indicate that’s all the work we have.</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="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">j</span> <span class="o"><=</span> <span class="nx">numJobs</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
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<span class="nx">jobs</span> <span class="o"><-</span> <span class="nx">j</span>
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<span class="p">}</span>
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<span class="nb">close</span><span class="p">(</span><span class="nx">jobs</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>Finally we collect all the results of the work.
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This also ensures that the worker goroutines have
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finished. An alternative way to wait for multiple
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goroutines is to use a <a href="waitgroups">WaitGroup</a>.</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="k">for</span> <span class="nx">a</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">a</span> <span class="o"><=</span> <span class="nx">numJobs</span><span class="p">;</span> <span class="nx">a</span><span class="o">++</span> <span class="p">{</span>
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<span class="o"><-</span><span class="nx">results</span>
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<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>Our running program shows the 5 jobs being executed by
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various workers. The program only takes about 2 seconds
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despite doing about 5 seconds of total work because
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there are 3 workers operating concurrently.</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="gp">$</span> time go run worker-pools.go
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<span class="go">worker 1 started job 1
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</span><span class="go">worker 2 started job 2
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</span><span class="go">worker 3 started job 3
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</span><span class="go">worker 1 finished job 1
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</span><span class="go">worker 1 started job 4
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</span><span class="go">worker 2 finished job 2
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</span><span class="go">worker 2 started job 5
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</span><span class="go">worker 3 finished job 3
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</span><span class="go">worker 1 finished job 4
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</span><span class="go">worker 2 finished job 5</span></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">
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<pre class="chroma"><span class="go">real 0m2.358s</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="waitgroups">WaitGroups</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 worker(id int, jobs \u003C-chan int, results chan\u003C- int) {\u000A for j :\u003D range jobs {\u000A fmt.Println(\"worker\", id, \"started job\", j)\u000A time.Sleep(time.Second)\u000A fmt.Println(\"worker\", id, \"finished job\", j)\u000A results \u003C- j * 2\u000A }\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' const numJobs \u003D 5\u000A jobs :\u003D make(chan int, numJobs)\u000A results :\u003D make(chan int, numJobs)\u000A');codeLines.push(' for w :\u003D 1; w \u003C\u003D 3; w++ {\u000A go worker(w, jobs, results)\u000A }\u000A');codeLines.push(' for j :\u003D 1; j \u003C\u003D numJobs; j++ {\u000A jobs \u003C- j\u000A }\u000A close(jobs)\u000A');codeLines.push(' for a :\u003D 1; a \u003C\u003D numJobs; a++ {\u000A \u003C-results\u000A }\u000A}\u000A');codeLines.push('');codeLines.push('');
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