9e216da9ef
After go1.16, go will use module mode by default, even when the repository is checked out under GOPATH or in a one-off directory. Add go.mod, go.sum to keep this repo buildable without opting out of the module mode. > go mod init github.com/mmcgrana/gobyexample > go mod tidy > go mod vendor In module mode, the 'vendor' directory is special and its contents will be actively maintained by the go command. pygments aren't the dependency the go will know about, so it will delete the contents from vendor directory. Move it to `third_party` directory now. And, vendor the blackfriday package. Note: the tutorial contents are not affected by the change in go1.16 because all the examples in this tutorial ask users to run the go command with the explicit list of files to be compiled (e.g. `go run hello-world.go` or `go build command-line-arguments.go`). When the source list is provided, the go command does not have to compute the build list and whether it's running in GOPATH mode or module mode becomes irrelevant.
202 lines
8.3 KiB
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202 lines
8.3 KiB
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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: Closing Channels</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 = 'non-blocking-channel-operations';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'range-over-channels';
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}
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}
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</script>
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<body>
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<div class="example" id="closing-channels">
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<h2><a href="./">Go by Example</a>: Closing Channels</h2>
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<table>
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<tr>
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<td class="docs">
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<p><em>Closing</em> a channel indicates that no more values
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will be sent on it. This can be useful to communicate
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completion to the channel’s receivers.</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/vCvRjcMq7p3"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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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">"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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<p>In this example we’ll use a <code>jobs</code> channel to
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communicate work to be done from the <code>main()</code> goroutine
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to a worker goroutine. When we have no more jobs for
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the worker we’ll <code>close</code> the <code>jobs</code> channel.</p>
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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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<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="mi">5</span><span class="p">)</span>
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<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>
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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>Here’s the worker goroutine. It repeatedly receives
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from <code>jobs</code> with <code>j, more := <-jobs</code>. In this
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special 2-value form of receive, the <code>more</code> value
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will be <code>false</code> if <code>jobs</code> has been <code>close</code>d and all
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values in the channel have already been received.
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We use this to notify on <code>done</code> when we’ve worked
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all our jobs.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">for</span> <span class="p">{</span>
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<span class="nx">j</span><span class="p">,</span> <span class="nx">more</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">jobs</span>
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<span class="k">if</span> <span class="nx">more</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">"received job"</span><span class="p">,</span> <span class="nx">j</span><span class="p">)</span>
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<span class="p">}</span> <span class="k">else</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">"received all jobs"</span><span class="p">)</span>
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<span class="nx">done</span> <span class="o"><-</span> <span class="kc">true</span>
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<span class="k">return</span>
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<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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<tr>
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<td class="docs">
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<p>This sends 3 jobs to the worker over the <code>jobs</code>
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channel, then closes it.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <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="mi">3</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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"sent job"</span><span class="p">,</span> <span class="nx">j</span><span class="p">)</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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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"sent all jobs"</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>We await the worker using the
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<a href="channel-synchronization">synchronization</a> approach
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we saw earlier.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="o"><-</span><span class="nx">done</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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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="gp">$</span> go run closing-channels.go
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<span class="go">sent job 1</span>
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<span class="go">received job 1</span>
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<span class="go">sent job 2</span>
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<span class="go">received job 2</span>
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<span class="go">sent job 3</span>
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<span class="go">received job 3</span>
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<span class="go">sent all jobs</span>
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<span class="go">received all jobs</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 idea of closed channels leads naturally to our next
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example: <code>range</code> over channels.</p>
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</td>
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<td class="code empty">
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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="range-over-channels">Range over Channels</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/closing-channels">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 \"fmt\"\u000A');codeLines.push('func main() {\u000A jobs :\u003D make(chan int, 5)\u000A done :\u003D make(chan bool)\u000A');codeLines.push(' go func() {\u000A for {\u000A j, more :\u003D \u003C-jobs\u000A if more {\u000A fmt.Println(\"received job\", j)\u000A } else {\u000A fmt.Println(\"received all jobs\")\u000A done \u003C- true\u000A return\u000A }\u000A }\u000A }()\u000A');codeLines.push(' for j :\u003D 1; j \u003C\u003D 3; j++ {\u000A jobs \u003C- j\u000A fmt.Println(\"sent job\", j)\u000A }\u000A close(jobs)\u000A fmt.Println(\"sent all jobs\")\u000A');codeLines.push(' \u003C-done\u000A}\u000A');codeLines.push('');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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