190 lines
9.6 KiB
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Generated
190 lines
9.6 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 в примерах: Тайм-ауты (Timeouts)</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 = 'select';
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if (e.key == "ArrowRight") {
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window.location.href = 'non-blocking-channel-operations';
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<body>
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<div class="example" id="timeouts">
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<h2><a href="./">Go в примерах</a>: Тайм-ауты (Timeouts)</h2>
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<table>
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<tr>
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<td class="docs">
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<p><em>Тайм-ауты</em> важны для программ, которые подключаются
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к внешним ресурсам или которым необходимо ограничить
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время выполнения. Тайм-ауты в Go реализуются легко
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и элегантно благодаря каналам и <code>select</code>‘ам.</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/SCMyPsGlXtX" 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="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></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>В нашем примере предположим, что мы выполняем внешний
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вызов, который возвращает результат на канале <code>c1</code>
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через 2с. Обратите внимание, что канал буферизован,
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поэтому отправка в goroutine неблокирующая. Это
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обычная схема предотвращения утечек горутин в случае,
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если канал никогда не читается.ё</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">c1</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> <span class="mi">1</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="nx">time</span><span class="p">.</span><span class="nx">Sleep</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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<span class="nx">c1</span> <span class="o"><-</span> <span class="s">"result 1"</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>Вот <code>select</code>, реализующий тайм-аут. <code>res := <-c1</code>
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ожидает результата, а <code><-Time.After</code> ожидает
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значения, которое будет отправлено после истечения
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времени ожидания 1с. Поскольку <code>select</code> продолжает
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работу с первым полученным запросом, мы возьмем
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тайм-аут, если операция займет больше разрешенных 1с.</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">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c1</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="nx">res</span><span class="p">)</span>
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<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nx">After</span><span class="p">(</span><span class="mi">1</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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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"timeout 1"</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>Если мы допустим время ожидания более 3с, то
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получение от <code>c2</code> будет успешным, и мы распечатаем
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результат.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">c2</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> <span class="mi">1</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="nx">time</span><span class="p">.</span><span class="nx">Sleep</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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<span class="nx">c2</span> <span class="o"><-</span> <span class="s">"result 2"</span>
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<span class="p">}()</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">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c2</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="nx">res</span><span class="p">)</span>
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<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nx">After</span><span class="p">(</span><span class="mi">3</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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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"timeout 2"</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>Запуск этой программы показывает время ожидания
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первой и второй успешной операции.</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 timeouts.go
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<span class="go">timeout 1</span>
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<span class="go">result 2</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="non-blocking-channel-operations">Неблокируемые операции в каналах (Non-Blocking Channel Operations)</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/timeouts">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 main() {\u000A');codeLines.push(' c1 := make(chan string, 1)\u000A go func() {\u000A time.Sleep(2 * time.Second)\u000A c1 \x3C- \"result 1\"\u000A }()\u000A');codeLines.push(' select {\u000A case res := \x3C-c1:\u000A fmt.Println(res)\u000A case \x3C-time.After(1 * time.Second):\u000A fmt.Println(\"timeout 1\")\u000A }\u000A');codeLines.push(' c2 := make(chan string, 1)\u000A go func() {\u000A time.Sleep(2 * time.Second)\u000A c2 \x3C- \"result 2\"\u000A }()\u000A select {\u000A case res := \x3C-c2:\u000A fmt.Println(res)\u000A case \x3C-time.After(3 * time.Second):\u000A fmt.Println(\"timeout 2\")\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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