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189 lines
9.3 KiB
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<!DOCTYPE html>
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<html>
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<meta charset="utf-8">
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<title>Go в примерах: Неблокируемые операции в каналах (Non-Blocking Channel Operations)</title>
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window.location.href = 'timeouts';
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window.location.href = 'closing-channels';
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<div class="example" id="non-blocking-channel-operations">
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<h2><a href="./">Go в примерах</a>: Неблокируемые операции в каналах (Non-Blocking Channel Operations)</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Стандартные отправители и получатели в каналах
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являются блокирующими.Тем не менее, мы можем
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использовать <code>select</code> с выбором <code>по умолчанию</code> для
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реализации <em>неблокирующих</em> отправителей, получателей
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и даже неблокирующего множественного <code>select</code>‘а.</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/FokCtF5TvgL" target="_blank"><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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</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">messages</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">string</span><span class="p">)</span>
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<span class="nx">signals</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>Вот неблокирующее получение. Если значение
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доступно в <code>messages</code>, тогда <code>select</code> выберет
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<code><-messages</code> с этим значением. Если нет, он
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сразу же примет случай <code>по-умолчанию</code>.</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">select</span> <span class="p">{</span>
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<span class="k">case</span> <span class="nx">msg</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">messages</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 message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
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<span class="k">default</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">"no message received"</span><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>Неблокирующая отправка работает аналогично.
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Здесь <code>msg</code> не может быть отправлено в канал
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<code>messages</code>, потому что у канала нет буфера и
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нет получателя. Поэтому выбирается действие
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<code>по-умолчанию</code>.</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">msg</span> <span class="o">:=</span> <span class="s">"hi"</span>
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<span class="k">select</span> <span class="p">{</span>
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<span class="k">case</span> <span class="nx">messages</span> <span class="o"><-</span> <span class="nx">msg</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 message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
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<span class="k">default</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">"no message sent"</span><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>Мы можем использовать несколько <code>case</code>‘ов перед
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<code>действием по-умолчанию</code> для реализации
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многоцелевого неблокирующего выбора. Здесь мы
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пытаемся получить неблокирующее получение
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<code>messages</code> и <code>signals</code>.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="k">select</span> <span class="p">{</span>
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<span class="k">case</span> <span class="nx">msg</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">messages</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 message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
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<span class="k">case</span> <span class="nx">sig</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">signals</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 signal"</span><span class="p">,</span> <span class="nx">sig</span><span class="p">)</span>
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<span class="k">default</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">"no activity"</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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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run non-blocking-channel-operations.go
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<span class="go">no message received</span>
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<span class="go">no message sent</span>
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<span class="go">no activity</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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Следующий пример: <a href="closing-channels">Закрытие каналов (Closing 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/non-blocking-channel-operations">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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<br/>
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переведено Nick S. | <a href="https://github.com/badkaktus/gobyexample">исходники</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 messages := make(chan string)\u000A signals := make(chan bool)\u000A');codeLines.push(' select {\u000A case msg := \x3C-messages:\u000A fmt.Println(\"received message\", msg)\u000A default:\u000A fmt.Println(\"no message received\")\u000A }\u000A');codeLines.push(' msg := \"hi\"\u000A select {\u000A case messages \x3C- msg:\u000A fmt.Println(\"sent message\", msg)\u000A default:\u000A fmt.Println(\"no message sent\")\u000A }\u000A');codeLines.push(' select {\u000A case msg := \x3C-messages:\u000A fmt.Println(\"received message\", msg)\u000A case sig := \x3C-signals:\u000A fmt.Println(\"received signal\", sig)\u000A default:\u000A fmt.Println(\"no activity\")\u000A }\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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