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Merge pull request #223 from eliben/addwaitgroup

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Add "Waiting For Goroutines To Finish" example.
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Mark McGranaghan 2019-05-30 06:23:53 -07:00 committed by GitHub
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12 changed files with 298 additions and 9 deletions
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1
examples.txt
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@ -32,6 +32,7 @@ Range over Channels
Timers
Tickers
Worker Pools
WaitGroups
Rate Limiting
Atomic Counters
Mutexes

2
examples/channel-synchronization/channel-synchronization.go
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@ -1,6 +1,8 @@
// We can use channels to synchronize execution
// across goroutines. Here's an example of using a
// blocking receive to wait for a goroutine to finish.
// When waiting for multiple goroutines to finish,
// you may prefer to use a [WaitGroup](waitgroups).
package main

4
examples/channel-synchronization/channel-synchronization.hash
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@ -1,2 +1,2 @@
fe3e2ea1a67d0f95ce4cb18f3e8aa16d416de0ce
0DfW-1RMqi
eb022977181884c2ab0f2b69e50311769e67a509
8lmP8beav0p

42
examples/waitgroups/waitgroups.go Normal file
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@ -0,0 +1,42 @@
// To wait for multiple goroutines to finish, we can
// use a *wait group*.
package main
import (
"fmt"
"sync"
"time"
)
// This is the function we'll run in every goroutine.
// Note that a WaitGroup must be passed to functions by
// pointer.
func worker(id int, wg *sync.WaitGroup) {
fmt.Printf("Worker %d starting\n", id)
// Sleep to simulate an expensive task.
time.Sleep(time.Second)
fmt.Printf("Worker %d done\n", id)
// Notify the WaitGroup that this worker is done.
wg.Done()
}
func main() {
// This WaitGroup is used to wait for all the
// goroutines launched here to finish.
var wg sync.WaitGroup
// Launch several goroutines and increment the WaitGroup
// counter for each.
for i := 1; i <= 5; i++ {
wg.Add(1)
go worker(i, &wg)
}
// Block until the WaitGroup counter goes back to 0;
// all the workers notified they're done.
wg.Wait()
}

2
examples/waitgroups/waitgroups.hash Normal file
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@ -0,0 +1,2 @@
499c7ee59b2ae06d2d3171768d9cf11762121a87
gLLmgcR7YkP

14
examples/waitgroups/waitgroups.sh Normal file
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@ -0,0 +1,14 @@
$ go run waitgroups.go
Worker 5 starting
Worker 3 starting
Worker 4 starting
Worker 1 starting
Worker 2 starting
Worker 4 done
Worker 1 done
Worker 2 done
Worker 5 done
Worker 3 done
# The order of workers starting up and finishing
# is likely to be different for each invocation.

3
examples/worker-pools/worker-pools.go
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@ -42,6 +42,9 @@ func main() {
close(jobs)
// Finally we collect all the results of the work.
// 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++ {
<-results
}

4
examples/worker-pools/worker-pools.hash
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@ -1,2 +1,2 @@
1f9acf1e50be05cad73e6b085ed3294892c67d42
RTRcHA05vV
bc69c6602d438413dcb9ceac112299ee253e4575
yuHsGf712D1

6
public/channel-synchronization
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@ -27,7 +27,9 @@
<td class="docs">
<p>We can use channels to synchronize execution
across goroutines. Here&rsquo;s an example of using a
blocking receive to wait for a goroutine to finish.</p>
blocking receive to wait for a goroutine to finish.
When waiting for multiple goroutines to finish,
you may prefer to use a <a href="waitgroups">WaitGroup</a>.</p>
</td>
<td class="code empty leading">
@ -41,7 +43,7 @@ blocking receive to wait for a goroutine to finish.</p>
</td>
<td class="code leading">
<a href="http://play.golang.org/p/0DfW-1RMqi"><img title="Run code" src="play.png" class="run" /></a>
<a href="http://play.golang.org/p/8lmP8beav0p"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>

2
public/index.html
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@ -103,6 +103,8 @@
<li><a href="worker-pools">Worker Pools</a></li>
<li><a href="waitgroups">WaitGroups</a></li>
<li><a href="rate-limiting">Rate Limiting</a></li>
<li><a href="atomic-counters">Atomic Counters</a></li>

218
public/waitgroups Normal file
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@ -0,0 +1,218 @@
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: WaitGroups</title>
<link rel=stylesheet href="site.css">
</head>
<script type="text/javascript">
if (window.location.host == "gobyexample.com") {
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-34996217-1']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
}
</script>
<body>
<div class="example" id="waitgroups">
<h2><a href="./">Go by Example</a>: WaitGroups</h2>
<table>
<tr>
<td class="docs">
<p>To wait for multiple goroutines to finish, we can
use a <em>wait group</em>.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/gLLmgcR7YkP"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;sync&quot;</span>
<span class="s">&quot;time&quot;</span>
<span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>This is the function we&rsquo;ll run in every goroutine.
Note that a WaitGroup must be passed to functions by
pointer.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">worker</span><span class="p">(</span><span class="nx">id</span> <span class="kt">int</span><span class="p">,</span> <span class="nx">wg</span> <span class="o">*</span><span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">&quot;Worker %d starting\n&quot;</span><span class="p">,</span> <span class="nx">id</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Sleep to simulate an expensive task.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">time</span><span class="p">.</span><span class="nx">Sleep</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">&quot;Worker %d done\n&quot;</span><span class="p">,</span> <span class="nx">id</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Notify the WaitGroup that this worker is done.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">wg</span><span class="p">.</span><span class="nx">Done</span><span class="p">()</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>This WaitGroup is used to wait for all the
goroutines launched here to finish.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">wg</span> <span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Launch several goroutines and increment the WaitGroup
counter for each.</p>
</td>
<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">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">wg</span><span class="p">.</span><span class="nx">Add</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">go</span> <span class="nx">worker</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span> <span class="o">&amp;</span><span class="nx">wg</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Block until the WaitGroup counter goes back to 0;
all the workers notified they&rsquo;re done.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">wg</span><span class="p">.</span><span class="nx">Wait</span><span class="p">()</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="gp">$</span> go run waitgroups.go
<span class="go">Worker 5 starting</span>
<span class="go">Worker 3 starting</span>
<span class="go">Worker 4 starting</span>
<span class="go">Worker 1 starting</span>
<span class="go">Worker 2 starting</span>
<span class="go">Worker 4 done</span>
<span class="go">Worker 1 done</span>
<span class="go">Worker 2 done</span>
<span class="go">Worker 5 done</span>
<span class="go">Worker 3 done</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>The order of workers starting up and finishing
is likely to be different for each invocation.</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
Next example: <a href="rate-limiting">Rate Limiting</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/waitgroups">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
</body>
</html>

9
public/worker-pools
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@ -40,7 +40,7 @@ a <em>worker pool</em> using goroutines and channels.</p>
</td>
<td class="code leading">
<a href="http://play.golang.org/p/RTRcHA05vV"><img title="Run code" src="play.png" class="run" /></a>
<a href="http://play.golang.org/p/yuHsGf712D1"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
@ -147,7 +147,10 @@ channel to indicate that&rsquo;s all the work we have.</p>
<tr>
<td class="docs">
<p>Finally we collect all the results of the work.</p>
<p>Finally we collect all the results of the work.
This also ensures that the worker goroutines have
finished. An alternative way to wait for multiple
goroutines is to use a <a href="waitgroups">WaitGroup</a>.</p>
</td>
<td class="code">
@ -207,7 +210,7 @@ there are 3 workers operating concurrently.</p>
<p class="next">
Next example: <a href="rate-limiting">Rate Limiting</a>.
Next example: <a href="waitgroups">WaitGroups</a>.
</p>
<p class="footer">