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<a href=".." >Fan-In</a>
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<h1 id="fan-in-messaging-patterns">Fan-In Messaging Patterns</h1>
<p>Fan-In is a messaging pattern used to create a funnel for work amongst workers (clients: source, server: destination).</p>
<p>We can model fan-in using the Go channels.</p>
<pre><code class="lang-go"><span class="hljs-comment">// Merge different channels in one channel</span>
<span class="hljs-keyword">func</span> Merge(cs ...&lt;-<span class="hljs-keyword">chan</span> <span class="hljs-keyword">int</span>) &lt;-<span class="hljs-keyword">chan</span> <span class="hljs-keyword">int</span> {
<span class="hljs-keyword">var</span> wg sync.WaitGroup
out := <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> <span class="hljs-keyword">int</span>)
<span class="hljs-comment">// Start an send goroutine for each input channel in cs. send</span>
<span class="hljs-comment">// copies values from c to out until c is closed, then calls wg.Done.</span>
send := <span class="hljs-keyword">func</span>(c &lt;-<span class="hljs-keyword">chan</span> <span class="hljs-keyword">int</span>) {
<span class="hljs-keyword">for</span> n := <span class="hljs-keyword">range</span> c {
out &lt;- n
}
wg.Done()
}
wg.Add(<span class="hljs-built_in">len</span>(cs))
<span class="hljs-keyword">for</span> _, c := <span class="hljs-keyword">range</span> cs {
<span class="hljs-keyword">go</span> send(c)
}
<span class="hljs-comment">// Start a goroutine to close out once all the send goroutines are</span>
<span class="hljs-comment">// done. This must start after the wg.Add call.</span>
<span class="hljs-keyword">go</span> <span class="hljs-keyword">func</span>() {
wg.Wait()
<span class="hljs-built_in">close</span>(out)
}()
<span class="hljs-keyword">return</span> out
}
</code></pre>
<p>The <code>Merge</code> function converts a list of channels to a single channel by starting a goroutine for each inbound channel that copies the values to the sole outbound channel.</p>
<p>Once all the output goroutines have been started, <code>Merge</code> a goroutine is started to close the main channel.</p>
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