646c8b39da
This bugfix implements correct way to calculate source sha1 hash, before it will changed, by propagation of unchanged sources. This commit will also include regenerated static files and *.hash files.
305 lines
14 KiB
Plaintext
Generated
305 lines
14 KiB
Plaintext
Generated
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta charset="utf-8">
|
|
<title>Go by Example: Mutexes</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script>
|
|
onkeydown = (e) => {
|
|
|
|
if (e.key == "ArrowLeft") {
|
|
window.location.href = 'atomic-counters';
|
|
}
|
|
|
|
|
|
if (e.key == "ArrowRight") {
|
|
window.location.href = 'stateful-goroutines';
|
|
}
|
|
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="mutexes">
|
|
<h2><a href="./">Go by Example</a>: Mutexes</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>In the previous example we saw how to manage simple
|
|
counter state using <a href="atomic-counters">atomic operations</a>.
|
|
For more complex state we can use a <em><a href="http://en.wikipedia.org/wiki/Mutual_exclusion">mutex</a></em>
|
|
to safely access data across multiple goroutines.</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/0WEmOOjoCjp"><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>
|
|
|
|
</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">"fmt"</span>
|
|
<span class="s">"math/rand"</span>
|
|
<span class="s">"sync"</span>
|
|
<span class="s">"sync/atomic"</span>
|
|
<span class="s">"time"</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>For our example the <code>state</code> will be a map.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">state</span> <span class="p">=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">map</span><span class="p">[</span><span class="kt">int</span><span class="p">]</span><span class="kt">int</span><span class="p">)</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>This <code>mutex</code> will synchronize access to <code>state</code>.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">mutex</span> <span class="p">=</span> <span class="o">&</span><span class="nx">sync</span><span class="p">.</span><span class="nx">Mutex</span><span class="p">{}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>We’ll keep track of how many read and write
|
|
operations we do.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">readOps</span> <span class="kt">uint64</span>
|
|
<span class="kd">var</span> <span class="nx">writeOps</span> <span class="kt">uint64</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Here we start 100 goroutines to execute repeated
|
|
reads against the state, once per millisecond in
|
|
each goroutine.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">r</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">r</span> <span class="p"><</span> <span class="mi">100</span><span class="p">;</span> <span class="nx">r</span><span class="o">++</span> <span class="p">{</span>
|
|
<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="nx">total</span> <span class="o">:=</span> <span class="mi">0</span>
|
|
<span class="k">for</span> <span class="p">{</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>For each read we pick a key to access,
|
|
<code>Lock()</code> the <code>mutex</code> to ensure
|
|
exclusive access to the <code>state</code>, read
|
|
the value at the chosen key,
|
|
<code>Unlock()</code> the mutex, and increment
|
|
the <code>readOps</code> count.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="nx">key</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
|
|
<span class="nx">mutex</span><span class="p">.</span><span class="nx">Lock</span><span class="p">()</span>
|
|
<span class="nx">total</span> <span class="o">+=</span> <span class="nx">state</span><span class="p">[</span><span class="nx">key</span><span class="p">]</span>
|
|
<span class="nx">mutex</span><span class="p">.</span><span class="nx">Unlock</span><span class="p">()</span>
|
|
<span class="nx">atomic</span><span class="p">.</span><span class="nx">AddUint64</span><span class="p">(</span><span class="o">&</span><span class="nx">readOps</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Wait a bit between reads.</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">Millisecond</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}()</span>
|
|
<span class="p">}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>We’ll also start 10 goroutines to simulate writes,
|
|
using the same pattern we did for reads.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">w</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">w</span> <span class="p"><</span> <span class="mi">10</span><span class="p">;</span> <span class="nx">w</span><span class="o">++</span> <span class="p">{</span>
|
|
<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="p">{</span>
|
|
<span class="nx">key</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
|
|
<span class="nx">val</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
|
|
<span class="nx">mutex</span><span class="p">.</span><span class="nx">Lock</span><span class="p">()</span>
|
|
<span class="nx">state</span><span class="p">[</span><span class="nx">key</span><span class="p">]</span> <span class="p">=</span> <span class="nx">val</span>
|
|
<span class="nx">mutex</span><span class="p">.</span><span class="nx">Unlock</span><span class="p">()</span>
|
|
<span class="nx">atomic</span><span class="p">.</span><span class="nx">AddUint64</span><span class="p">(</span><span class="o">&</span><span class="nx">writeOps</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
|
|
<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">Millisecond</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}()</span>
|
|
<span class="p">}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Let the 10 goroutines work on the <code>state</code> and
|
|
<code>mutex</code> for a second.</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>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Take and report final operation counts.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="nx">readOpsFinal</span> <span class="o">:=</span> <span class="nx">atomic</span><span class="p">.</span><span class="nx">LoadUint64</span><span class="p">(</span><span class="o">&</span><span class="nx">readOps</span><span class="p">)</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"readOps:"</span><span class="p">,</span> <span class="nx">readOpsFinal</span><span class="p">)</span>
|
|
<span class="nx">writeOpsFinal</span> <span class="o">:=</span> <span class="nx">atomic</span><span class="p">.</span><span class="nx">LoadUint64</span><span class="p">(</span><span class="o">&</span><span class="nx">writeOps</span><span class="p">)</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"writeOps:"</span><span class="p">,</span> <span class="nx">writeOpsFinal</span><span class="p">)</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>With a final lock of <code>state</code>, show how it ended up.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<div class="highlight"><pre> <span class="nx">mutex</span><span class="p">.</span><span class="nx">Lock</span><span class="p">()</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"state:"</span><span class="p">,</span> <span class="nx">state</span><span class="p">)</span>
|
|
<span class="nx">mutex</span><span class="p">.</span><span class="nx">Unlock</span><span class="p">()</span>
|
|
<span class="p">}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Running the program shows that we executed about
|
|
90,000 total operations against our <code>mutex</code>-synchronized
|
|
<code>state</code>.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="gp">$</span> go run mutexes.go
|
|
<span class="go">readOps: 83285</span>
|
|
<span class="go">writeOps: 8320</span>
|
|
<span class="go">state: map[1:97 4:53 0:33 2:15 3:2]</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Next we’ll look at implementing this same state
|
|
management task using only goroutines and channels.</p>
|
|
|
|
</td>
|
|
<td class="code empty">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
|
|
<p class="next">
|
|
Next example: <a href="stateful-goroutines">Stateful Goroutines</a>.
|
|
</p>
|
|
|
|
<p class="footer">
|
|
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/mutexes">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
|
|
</p>
|
|
</div>
|
|
<script>
|
|
var codeLines = [];
|
|
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"math/rand\"\u000A \"sync\"\u000A \"sync/atomic\"\u000A \"time\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' var state = make(map[int]int)\u000A');codeLines.push(' var mutex = &sync.Mutex{}\u000A');codeLines.push(' var readOps uint64\u000A var writeOps uint64\u000A');codeLines.push(' for r := 0; r \x3C 100; r++ {\u000A go func() {\u000A total := 0\u000A for {\u000A');codeLines.push(' key := rand.Intn(5)\u000A mutex.Lock()\u000A total += state[key]\u000A mutex.Unlock()\u000A atomic.AddUint64(&readOps, 1)\u000A');codeLines.push(' time.Sleep(time.Millisecond)\u000A }\u000A }()\u000A }\u000A');codeLines.push(' for w := 0; w \x3C 10; w++ {\u000A go func() {\u000A for {\u000A key := rand.Intn(5)\u000A val := rand.Intn(100)\u000A mutex.Lock()\u000A state[key] = val\u000A mutex.Unlock()\u000A atomic.AddUint64(&writeOps, 1)\u000A time.Sleep(time.Millisecond)\u000A }\u000A }()\u000A }\u000A');codeLines.push(' time.Sleep(time.Second)\u000A');codeLines.push(' readOpsFinal := atomic.LoadUint64(&readOps)\u000A fmt.Println(\"readOps:\", readOpsFinal)\u000A writeOpsFinal := atomic.LoadUint64(&writeOps)\u000A fmt.Println(\"writeOps:\", writeOpsFinal)\u000A');codeLines.push(' mutex.Lock()\u000A fmt.Println(\"state:\", state)\u000A mutex.Unlock()\u000A}\u000A');codeLines.push('');codeLines.push('');
|
|
</script>
|
|
<script src="site.js" async></script>
|
|
</body>
|
|
</html>
|