Remove magic numbers from code, explain use of buffered channels

examples/worker-pools/worker-pools.go

@@ -26,9 +26,13 @@ func main() {
 
 	// In order to use our pool of workers we need to send
 	// them work and collect their results. We make 2
-	// channels for this.
+	// channels for this.  We use buffered channels
-	jobs := make(chan int, 100)
+	// because we want the workers to block until they
-	results := make(chan int, 100)
+	// receive on the `jobs` channel, but want to be able
+	// to send to either channel without blocking.
+	const numJobs = 5
+	jobs := make(chan int, numJobs)
+	results := make(chan int, numJobs)
 
 	// This starts up 3 workers, initially blocked
 	// because there are no jobs yet.
@@ -38,7 +42,7 @@ func main() {
 
 	// Here we send 5 `jobs` and then `close` that
 	// channel to indicate that's all the work we have.
-	for j := 1; j <= 5; j++ {
+	for j := 1; j <= numJobs; j++ {
 		jobs <- j
 	}
 	close(jobs)
@@ -47,7 +51,7 @@ func main() {
 	// This also ensures that the worker goroutines have
 	// finished. An alternative way to wait for multiple
 	// goroutines is to use a [WaitGroup](waitgroups).
-	for a := 1; a <= 5; a++ {
+	for a := 1; a <= numJobs; a++ {
 		<-results
 	}
 }

examples/worker-pools/worker-pools.hash

@@ -1,2 +1,2 @@
-9b30cdfc3f46d634c3b8671a7ae1551c133fb6e2
+72be5c38dbcb94a7567baa43726a4c44cbd187ea
-IiKZ-nj-nKY
+OsX4R3HlGXG

public/worker-pools

@@ -42,7 +42,7 @@ a <em>worker pool</em> using goroutines and channels.</p>
             
           </td>
           <td class="code leading">
-            <a href="http://play.golang.org/p/IiKZ-nj-nKY"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
+            <a href="http://play.golang.org/p/OsX4R3HlGXG"><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>
 
@@ -104,13 +104,17 @@ simulate an expensive task.</p>
           <td class="docs">
             <p>In order to use our pool of workers we need to send
 them work and collect their results. We make 2
-channels for this.</p>
+channels for this.  We use buffered channels
+because we want the workers to block until they
+receive on the <code>jobs</code> channel, but want to be able
+to send to either channel without blocking.</p>
 
           </td>
           <td class="code leading">
             
-          <div class="highlight"><pre>    <span class="nx">jobs</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">100</span><span class="p">)</span>
+          <div class="highlight"><pre>    <span class="kd">const</span> <span class="nx">numJobs</span> <span class="p">=</span> <span class="mi">5</span>
-    <span class="nx">results</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">100</span><span class="p">)</span>
+    <span class="nx">jobs</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="nx">numJobs</span><span class="p">)</span>
+    <span class="nx">results</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="nx">numJobs</span><span class="p">)</span>
 </pre></div>
 
           </td>
@@ -140,7 +144,7 @@ channel to indicate that&rsquo;s all the work we have.</p>
           </td>
           <td class="code leading">
             
-          <div class="highlight"><pre>    <span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">j</span> <span class="o">&lt;=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
+          <div class="highlight"><pre>    <span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">j</span> <span class="o">&lt;=</span> <span class="nx">numJobs</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
         <span class="nx">jobs</span> <span class="o">&lt;-</span> <span class="nx">j</span>
     <span class="p">}</span>
     <span class="nb">close</span><span class="p">(</span><span class="nx">jobs</span><span class="p">)</span>
@@ -159,7 +163,7 @@ goroutines is to use a <a href="waitgroups">WaitGroup</a>.</p>
           </td>
           <td class="code">
             
-          <div class="highlight"><pre>    <span class="k">for</span> <span class="nx">a</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">a</span> <span class="o">&lt;=</span> <span class="mi">5</span><span class="p">;</span> <span class="nx">a</span><span class="o">++</span> <span class="p">{</span>
+          <div class="highlight"><pre>    <span class="k">for</span> <span class="nx">a</span> <span class="o">:=</span> <span class="mi">1</span><span class="p">;</span> <span class="nx">a</span> <span class="o">&lt;=</span> <span class="nx">numJobs</span><span class="p">;</span> <span class="nx">a</span><span class="o">++</span> <span class="p">{</span>
         <span class="o">&lt;-</span><span class="nx">results</span>
     <span class="p">}</span>
 <span class="p">}</span>
@@ -223,7 +227,7 @@ there are 3 workers operating concurrently.</p>
     </div>
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