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mutexes.html
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mutexes.html
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<!DOCTYPE html>
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<title>サンプルで学ぶ Go 言語：Mutexes</title>
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<h2><a href="./">サンプルで学ぶ Go 言語</a>：Mutexes</h2>
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<td class="docs">
<p>前の例で、単純なカウンタの状態を<a href="atomic-counters.html">アトミックな操作</a>で管理する方法を紹介した。
より複雑な状態を管理したいときには、<a href="http://en.wikipedia.org/wiki/Mutual_exclusion"><em>ミューテックス（mutex）</em></a>を使って複数のゴルーチンから安全にデータを読み書きすることもできる。</p>
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<td class="code leading">
<a href="http://play.golang.org/p/n0jkkY8bA0s"><img title="コードを実行する" 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>
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<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>
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<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>
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<td class="docs">
<p>状態の例としてマップを使う。</p>
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<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>
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<p>この <code>mutex</code> を使って、<code>state</code> へのアクセスを同期する。</p>
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<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>
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<p>読み操作・書き操作がそれぞれ何度行われたかをカウントする。</p>
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<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>
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<p>100 個のゴルーチンを作り、それぞれが1ミリ秒ごとに state を繰り返し読み出す。</p>
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<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>
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<p>読み出しのたびに、アクセスするキーを選ぶ。
<code>Lock()</code> で <code>mutex</code> をロックし、<code>state</code> への排他的なアクセスを獲得し、値を読み出し、<code>Unlock()</code> で <code>mutex</code> のロックを解除し、最後に <code>readOps</code> の値を1増やす。</p>
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<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>
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<p>読み出しのたびに少し待つ。</p>
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<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>
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<td class="docs">
<p>10個のゴルーチンを起動し、読み出しと同様のパターンで書き込みを行う。</p>
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<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>
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<td class="docs">
<p>10個のゴルーチンが <code>state</code> や <code>mutex</code> で仕事をできるよう、一秒待つ。</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>
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<td class="docs">
<p>結果を読み出して、読み書き操作のカウントを報告する</p>
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<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>
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<td class="docs">
<p><code>state</code> をロックして、最終的にどうなったかを表示する。</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>
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</table>
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<td class="docs">
<p>プログラムを実行した結果、<code>mutex</code> で同期した操作を合計で約90000回実行したことがわかる。</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>
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<td class="docs">
<p>続いて、同様の状態管理をゴルーチンとチャネルだけを使って実装する方法を紹介する。</p>
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<td class="code empty">
</td>
</tr>
</table>
<p class="next">
次の例：<a href="stateful-goroutines.html">Stateful Goroutines</a>
</p>
<p class="footer">
原著者 <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | 翻訳者：<a href="https://twitter.com/spinute">@spinute</a> | <a href="mailto:spinute.pages@gmail.com">フィードバック</a> | <a href="https://github.com/spinute/go-by-example/blob/master/docs/mutexes.html">ソースコード</a> | <a href="https://github.com/spinute/go-by-example#license">ライセンス</a>
</p>
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