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<header data-kunai-mdinfo="{"meta": {"header": ["shared_mutex"], "namespace": ["std"], "id-type": ["class"], "cpp": ["cpp17"]}, "sources": [{"id": "b82465076904338ca35d971f84a76e20fe0a86fc", "source": "#include <iostream>\n#include <thread>\n#include <mutex>\n#include <shared_mutex>\n#include <chrono>\n\nstd::mutex print_mtx;\nvoid print_value(int x)\n{\n std::lock_guard<std::mutex> lock(print_mtx);\n std::cout << x << std::endl;\n}\n\nclass X {\n std::shared_mutex mtx_;\n int count_ = 0;\npublic:\n // \u66f8\u304d\u8fbc\u307f\u5074\uff1a\u30ab\u30a6\u30f3\u30bf\u3092\u52a0\u7b97\u3059\u308b\n void writer()\n {\n std::lock_guard<std::shared_mutex> lock(mtx_);\n ++count_;\n }\n\n // \u8aad\u307f\u8fbc\u307f\u5074\uff1a\u30ab\u30a6\u30f3\u30bf\u306e\u5024\u3092\u8aad\u3080\n void reader()\n {\n int local_count;\n {\n std::shared_lock<std::shared_mutex> lock(mtx_);\n local_count = count_;\n } // \u5171\u6709\u30ed\u30c3\u30af\u3092\u3053\u3053\u3067\u624b\u653e\u3059\n print_value(local_count);\n }\n};\n\nX obj;\nvoid writer_thread()\n{\n for (int i = 0; i < 3; ++i) {\n std::this_thread::sleep_for(std::chrono::milliseconds(1));\n obj.writer();\n }\n}\n\nvoid reader_thread()\n{\n for (int i = 0; i < 10; ++i) {\n std::this_thread::sleep_for(std::chrono::milliseconds(1));\n obj.reader();\n }\n}\n\nint main()\n{\n // \u66f8\u304d\u8fbc\u307f\u30e6\u30fc\u30b6\u30fc1\u4eba\n // \u8aad\u307f\u8fbc\u307f\u30e6\u30fc\u30b6\u30fc3\u4eba\n std::thread writer1(writer_thread);\n std::thread reader1(reader_thread);\n std::thread reader2(reader_thread);\n std::thread reader3(reader_thread);\n\n writer1.join();\n reader1.join();\n reader2.join();\n reader3.join();\n}\n"}], "page_id": ["reference", "shared_mutex", "shared_mutex"]}">
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<div class="identifier-type">class</div><div class="header"><shared_mutex></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">shared_mutex</span><span class="cpp cpp17" title="C++17で追加">(C++17)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">shared_mutex</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>shared_mutex</code>クラスは、<a href="https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock" target="_blank">Readers-writer lock</a>パターンをサポートするミューテックスクラスである。</p>
<p>このパターンは、「複数のユーザーによる読み込みと、単一ユーザーによる書き込み」の排他制御を効率的に行う、というものである。</p>
<p>このミューテックスクラスのロック取得方法は2種類ある。</p>
<ul>
<li><code><a href="shared_mutex/lock.html">lock()</a></code>／<code><a href="shared_mutex/unlock.html">unlock()</a></code>メンバ関数：書き込み用のロックを取得する</li>
<li><code><a href="shared_mutex/lock_shared.html">lock_shared()</a></code>／<code><a href="shared_mutex/unlock_shared.html">unlock_shared()</a></code>メンバ関数：読み込み用のロックを取得する</li>
</ul>
<p>このクラスは、デストラクタで自動的にロックを手放すことはしない。そのため、以下の補助クラスを使用して、デストラクタで自動的にロックを手放す。</p>
<ul>
<li><code><a href="../mutex/lock_guard.html">lock_guard</a></code>クラス／<code><a href="../mutex/unique_lock.html">unique_lock</a></code>クラス：書き込み用のロックを自動的に手放す</li>
<li><code><a href="shared_lock.html">shared_lock</a></code>：読み込み用のロックを自動的に手放す</li>
</ul>
<h2>備考</h2>
<ul>
<li>このクラスは現状、書き込みロックと読み込みロックについてのスケジューリング戦略を規定せず、カスタマイズもできない。そのため、書き込みロックがなかなか取得できない、読み込みロックがなかなか取得できないというスタベーションの問題が発生した場合に、ユーザーの状況に合わせて戦略を変更することができない。POSIXのReaders-writer lockの実装では、スケジューリングのオプションを指定できる<ul>
<li><code><a href="https://web.archive.org/web/20230130174238/http://linuxjm.osdn.jp/html/LDP_man-pages/man3/pthread_rwlockattr_setkind_np.3.html" target="_blank">pthread_rwlockattr_setkind_np()</a></code></li>
</ul>
</li>
</ul>
<h2>メンバ関数</h2>
<h3>構築・破棄</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="shared_mutex/op_constructor.html">(constructor)</a></code></td>
<td>コンストラクタ</td>
<td>C++17</td>
</tr>
<tr>
<td><code><a href="shared_mutex/op_destructor.html">(destructor)</a></code></td>
<td>デストラクタ</td>
<td>C++17</td>
</tr>
<tr>
<td><code>operator=(const shared_mutex&) = delete;</code></td>
<td>代入演算子</td>
<td>C++17</td>
</tr>
</tbody>
</table>
<h3>排他の所有権</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="shared_mutex/lock.html">lock</a></code></td>
<td>排他ロックを取得する</td>
<td>C++17</td>
</tr>
<tr>
<td><code><a href="shared_mutex/try_lock.html">try_lock</a></code></td>
<td>排他ロックの取得を試みる</td>
<td>C++17</td>
</tr>
<tr>
<td><code><a href="shared_mutex/unlock.html">unlock</a></code></td>
<td>排他ロックを手放す</td>
<td>C++17</td>
</tr>
</tbody>
</table>
<h3>共有の所有権</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>名前</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="shared_mutex/lock_shared.html">lock_shared</a></code></td>
<td>共有ロックを取得する</td>
<td>C++17</td>
</tr>
<tr>
<td><code><a href="shared_mutex/try_lock_shared.html">try_lock_shared</a></code></td>
<td>共有ロックの取得を試みる</td>
<td>C++17</td>
</tr>
<tr>
<td><code><a href="shared_mutex/unlock_shared.html">unlock_shared</a></code></td>
<td>共有ロックを手放す</td>
<td>C++17</td>
</tr>
</tbody>
</table>
<h2>例</h2>
<p><div class="yata" id="b82465076904338ca35d971f84a76e20fe0a86fc"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../thread.html"><thread></a></span>
<span class="cp">#include <a href="../mutex.html"><mutex></a></span>
<span class="cp">#include <a href="../shared_mutex.html"><shared_mutex></a></span>
<span class="cp">#include <a href="../chrono.html"><chrono></a></span>
<span class="n"><a href="../mutex/mutex.html">std::mutex</a></span><span class="w"> </span><span class="n">print_mtx</span><span class="p">;</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">print_value</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../mutex/lock_guard.html">std::lock_guard</a></span><span class="o"><</span><span class="n"><a href="../mutex/mutex.html">std::mutex</a></span><span class="o">></span><span class="w"> </span><span class="n">lock</span><span class="p">(</span><span class="n">print_mtx</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">class</span><span class="w"> </span><span class="nc">X</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::shared_mutex</span></span><span class="w"> </span><span class="n">mtx_</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="k">public</span><span class="o">:</span>
<span class="w"> </span><span class="c1">// 書き込み側：カウンタを加算する</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">writer</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../mutex/lock_guard.html">std::lock_guard</a></span><span class="o"><</span><span class="n"><span style="color:#ff0000">std::shared_mutex</span></span><span class="o">></span><span class="w"> </span><span class="n">lock</span><span class="p">(</span><span class="n">mtx_</span><span class="p">);</span>
<span class="w"> </span><span class="o">++</span><span class="n">count_</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// 読み込み側：カウンタの値を読む</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">reader</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">local_count</span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="shared_lock.html">std::shared_lock</a></span><span class="o"><</span><span class="n"><span style="color:#ff0000">std::shared_mutex</span></span><span class="o">></span><span class="w"> </span><span class="n">lock</span><span class="p">(</span><span class="n">mtx_</span><span class="p">);</span>
<span class="w"> </span><span class="n">local_count</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">count_</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="c1">// 共有ロックをここで手放す</span>
<span class="w"> </span><span class="n">print_value</span><span class="p">(</span><span class="n">local_count</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="n">X</span><span class="w"> </span><span class="n">obj</span><span class="p">;</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">writer_thread</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../thread/this_thread/sleep_for.html">std::this_thread::sleep_for</a></span><span class="p">(</span><span class="n"><a href="../chrono/duration_aliases.html">std::chrono::milliseconds</a></span><span class="p">(</span><span class="mi">1</span><span class="p">));</span>
<span class="w"> </span><span class="n">obj</span><span class="p">.</span><span class="n">writer</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">reader_thread</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../thread/this_thread/sleep_for.html">std::this_thread::sleep_for</a></span><span class="p">(</span><span class="n"><a href="../chrono/duration_aliases.html">std::chrono::milliseconds</a></span><span class="p">(</span><span class="mi">1</span><span class="p">));</span>
<span class="w"> </span><span class="n">obj</span><span class="p">.</span><span class="n">reader</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// 書き込みユーザー1人</span>
<span class="w"> </span><span class="c1">// 読み込みユーザー3人</span>
<span class="w"> </span><span class="n"><a href="../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="n">writer1</span><span class="p">(</span><span class="n">writer_thread</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="n">reader1</span><span class="p">(</span><span class="n">reader_thread</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="n">reader2</span><span class="p">(</span><span class="n">reader_thread</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="n">reader3</span><span class="p">(</span><span class="n">reader_thread</span><span class="p">);</span>
<span class="w"> </span><span class="n">writer1</span><span class="p">.</span><span class="n"><a href="../thread/thread/join.html">join()</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">reader1</span><span class="p">.</span><span class="n"><a href="../thread/thread/join.html">join()</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">reader2</span><span class="p">.</span><span class="n"><a href="../thread/thread/join.html">join()</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">reader3</span><span class="p">.</span><span class="n"><a href="../thread/thread/join.html">join()</a></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力例</h3>
<p><pre><code>1
1
1
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++17</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 3.7.1 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>: 6.3 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#icc">ICC</a>: ??</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="shared_timed_mutex.html">std::shared_timed_mutex</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock" target="_blank">Readers–writer lock - Wikipedia</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4508.html" target="_blank">N4508: A proposal to add <code>shared_mutex</code> (untimed)</a></li>
</ul></div>
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