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2019-10-15 15:02:01 +03:00

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<title>Go в примерах: Ограничение скорости (Rate Limiting)</title>
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<div class="example" id="rate-limiting">
<h2><a href="./">Go в примерах</a>: Ограничение скорости (Rate Limiting)</h2>
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<td class="docs">
<p><em><a href="http://en.wikipedia.org/wiki/Rate_limiting">Ограничение скорости</a></em>
является важным механизмом контроля использования ресурсов и
поддержания качества обслуживания. Go элегантно поддерживает
ограничение скорости с помощью горутин, каналов и <a href="tickers">тикеров</a>.</p>
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<a href="http://play.golang.org/p/rC0qLhImKAo" target="_blank"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<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="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;time&quot;</span>
<span class="p">)</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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<td class="docs">
<p>Сначала мы рассмотрим базовое ограничение скорости.
Предположим, мы хотим ограничить нашу обработку
входящих запросов. Мы будем обслуживать эти запросы
с одноименного канала.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">requests</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>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">i</span> <span class="o">&lt;=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">requests</span> <span class="o">&lt;-</span> <span class="nx">i</span>
<span class="p">}</span>
<span class="nb">close</span><span class="p">(</span><span class="nx">requests</span><span class="p">)</span>
</pre></div>
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<p>Канал <code>limiter</code> будет получать значение каждые
200мс. Это то, что регулирует скорость в нашей
схеме.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">limiter</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Tick</span><span class="p">(</span><span class="mi">200</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span>
</pre></div>
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<p>Блокируя прием от канала <code>limiter</code> перед
обслуживанием каждого запроса, мы ограничиваем себя
одним запросом каждые 200 миллисекунд.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">req</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">requests</span> <span class="p">{</span>
<span class="o">&lt;-</span><span class="nx">limiter</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;request&quot;</span><span class="p">,</span> <span class="nx">req</span><span class="p">,</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">())</span>
<span class="p">}</span>
</pre></div>
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<p>Мы можем разрешить короткие всплески запросов в
нашей схеме ограничения скорости при сохранении
общего ограничения скорости. Мы можем сделать это
путем буферизации нашего канала ограничения. Этот
канал <code>burstyLimiter</code> будет позволять делать до
3 событий.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">burstyLimiter</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Time</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
</pre></div>
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<p>Заполняем канал, чтобы предоставить возможность
ускорить.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p">&lt;</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">burstyLimiter</span> <span class="o">&lt;-</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">()</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p>Каждые 200мс мы будем пытаться добавлять новое
значение в <code>burstyLimiter</code>, до своего предела
в 3 значения.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">for</span> <span class="nx">t</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Tick</span><span class="p">(</span><span class="mi">200</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Millisecond</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">burstyLimiter</span> <span class="o">&lt;-</span> <span class="nx">t</span>
<span class="p">}</span>
<span class="p">}()</span>
</pre></div>
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<td class="docs">
<p>Теперь смоделируем еще 5 входящих запросов. Первые
3 из них получат выгоду от вместимости <code>burstyLimiter</code>.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">burstyRequests</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>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">i</span> <span class="o">&lt;=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">burstyRequests</span> <span class="o">&lt;-</span> <span class="nx">i</span>
<span class="p">}</span>
<span class="nb">close</span><span class="p">(</span><span class="nx">burstyRequests</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">req</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">burstyRequests</span> <span class="p">{</span>
<span class="o">&lt;-</span><span class="nx">burstyLimiter</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;request&quot;</span><span class="p">,</span> <span class="nx">req</span><span class="p">,</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">())</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p>При запуске нашей программы мы видим, что первая
партия запросов обрабатывается каждые ~200мс.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="gp">$</span> go run rate-limiting.go
<span class="go">request 1 2012-10-19 00:38:18.687438 +0000 UTC</span>
<span class="go">request 2 2012-10-19 00:38:18.887471 +0000 UTC</span>
<span class="go">request 3 2012-10-19 00:38:19.087238 +0000 UTC</span>
<span class="go">request 4 2012-10-19 00:38:19.287338 +0000 UTC</span>
<span class="go">request 5 2012-10-19 00:38:19.487331 +0000 UTC</span>
</pre></div>
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<td class="docs">
<p>Для второго пула запросов мы обслуживаем первые
3 сразу из-за использования ограничения скорости,
затем обслуживаем оставшиеся 2 с задержками ~200мс
каждый.</p>
</td>
<td class="code">
<div class="highlight"><pre><span class="go">request 1 2012-10-19 00:38:20.487578 +0000 UTC</span>
<span class="go">request 2 2012-10-19 00:38:20.487645 +0000 UTC</span>
<span class="go">request 3 2012-10-19 00:38:20.487676 +0000 UTC</span>
<span class="go">request 4 2012-10-19 00:38:20.687483 +0000 UTC</span>
<span class="go">request 5 2012-10-19 00:38:20.887542 +0000 UTC</span>
</pre></div>
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</tr>
</table>
<p class="next">
Следующий пример: <a href="atomic-counters">Атомарные счетчики (Atomic Counters)</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/rate-limiting">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
<br/>
переведено Nick S. | <a href="https://github.com/badkaktus/gobyexample">исходники</a>
</p>
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