266 lines
12 KiB
Plaintext
Generated
266 lines
12 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<meta charset="utf-8">
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<title>Go by Example: Rate Limiting</title>
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<div class="example" id="rate-limiting">
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<h2><a href="./">Go by Example</a>: Rate Limiting</h2>
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<table>
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<tr>
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<td class="docs">
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<p><a href="http://en.wikipedia.org/wiki/Rate_limiting"><em>Rate limiting</em></a>
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is an important mechanism for controlling resource
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utilization and maintaining quality of service. Go
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elegantly supports rate limiting with goroutines,
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channels, and <a href="tickers">tickers</a>.</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/GXjXHfnKFXg"><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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</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>First we’ll look at basic rate limiting. Suppose
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we want to limit our handling of incoming requests.
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We’ll serve these requests off a channel of the
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same name.</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="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>
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<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"><=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
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<span class="nx">requests</span> <span class="o"><-</span> <span class="nx">i</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">requests</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 <code>limiter</code> channel will receive a value
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every 200 milliseconds. This is the regulator in
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our rate limiting scheme.</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="nx">limiter</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nf">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>
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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>By blocking on a receive from the <code>limiter</code> channel
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before serving each request, we limit ourselves to
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1 request every 200 milliseconds.</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">req</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">requests</span> <span class="p">{</span>
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<span class="o"><-</span><span class="nx">limiter</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">"request"</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="nf">Now</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>We may want to allow short bursts of requests in
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our rate limiting scheme while preserving the
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overall rate limit. We can accomplish this by
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buffering our limiter channel. This <code>burstyLimiter</code>
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channel will allow bursts of up to 3 events.</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="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>
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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>Fill up the channel to represent allowed bursting.</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">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
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<span class="nx">burstyLimiter</span> <span class="o"><-</span> <span class="nx">time</span><span class="p">.</span><span class="nf">Now</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>Every 200 milliseconds we’ll try to add a new
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value to <code>burstyLimiter</code>, up to its limit of 3.</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">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="nx">t</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">time</span><span class="p">.</span><span class="nf">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>
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<span class="nx">burstyLimiter</span> <span class="o"><-</span> <span class="nx">t</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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<p>Now simulate 5 more incoming requests. The first
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3 of these will benefit from the burst capability
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of <code>burstyLimiter</code>.</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="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>
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<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"><=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
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<span class="nx">burstyRequests</span> <span class="o"><-</span> <span class="nx">i</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">burstyRequests</span><span class="p">)</span>
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<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>
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<span class="o"><-</span><span class="nx">burstyLimiter</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">"request"</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="nf">Now</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>
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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>Running our program we see the first batch of requests
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handled once every ~200 milliseconds as desired.</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> go run rate-limiting.go
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<span class="go">request 1 2012-10-19 00:38:18.687438 +0000 UTC
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</span><span class="go">request 2 2012-10-19 00:38:18.887471 +0000 UTC
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</span><span class="go">request 3 2012-10-19 00:38:19.087238 +0000 UTC
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</span><span class="go">request 4 2012-10-19 00:38:19.287338 +0000 UTC
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</span><span class="go">request 5 2012-10-19 00:38:19.487331 +0000 UTC</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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<p>For the second batch of requests we serve the first
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3 immediately because of the burstable rate limiting,
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then serve the remaining 2 with ~200ms delays each.</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="go">request 1 2012-10-19 00:38:20.487578 +0000 UTC
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</span><span class="go">request 2 2012-10-19 00:38:20.487645 +0000 UTC
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</span><span class="go">request 3 2012-10-19 00:38:20.487676 +0000 UTC
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</span><span class="go">request 4 2012-10-19 00:38:20.687483 +0000 UTC
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</span><span class="go">request 5 2012-10-19 00:38:20.887542 +0000 UTC</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="atomic-counters">Atomic Counters</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 main() {\u000A');codeLines.push(' requests :\u003D make(chan int, 5)\u000A for i :\u003D 1; i \u003C\u003D 5; i++ {\u000A requests \u003C- i\u000A }\u000A close(requests)\u000A');codeLines.push(' limiter :\u003D time.Tick(200 * time.Millisecond)\u000A');codeLines.push(' for req :\u003D range requests {\u000A \u003C-limiter\u000A fmt.Println(\"request\", req, time.Now())\u000A }\u000A');codeLines.push(' burstyLimiter :\u003D make(chan time.Time, 3)\u000A');codeLines.push(' for i :\u003D 0; i \u003C 3; i++ {\u000A burstyLimiter \u003C- time.Now()\u000A }\u000A');codeLines.push(' go func() {\u000A for t :\u003D range time.Tick(200 * time.Millisecond) {\u000A burstyLimiter \u003C- t\u000A }\u000A }()\u000A');codeLines.push(' burstyRequests :\u003D make(chan int, 5)\u000A for i :\u003D 1; i \u003C\u003D 5; i++ {\u000A burstyRequests \u003C- i\u000A }\u000A close(burstyRequests)\u000A for req :\u003D range burstyRequests {\u000A \u003C-burstyLimiter\u000A fmt.Println(\"request\", req, time.Now())\u000A }\u000A}\u000A');codeLines.push('');codeLines.push('');
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</script>
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