188 lines
13 KiB
HTML
188 lines
13 KiB
HTML
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<title>std::recursive_mutex</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_recursive_mutex skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>recursive_mutex</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-thread.html">thread</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-mutex.html"><mutex></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> recursive_mutex<span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p><code>recursive_mutex</code> 类是同步原语，能用于保护共享数据免受从个多线程同时访问。</p>
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<p><code>recursive_mutex</code> 提供排他性递归所有权语义：</p>
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<ul>
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<li>调用方线程在从它成功调用 <a href="cpp-thread-recursive_mutex-lock.html"><code>lock</code></a> 或 <a href="cpp-thread-mutex-try_lock.html"><code>try_lock</code></a> 开始的时期里<i>占有</i> <code>recursive_mutex</code> 。此时期间，线程可以进行对 <a href="cpp-thread-recursive_mutex-lock.html"><code>lock</code></a> 或 <a href="cpp-thread-recursive_mutex-try_lock.html"><code>try_lock</code></a> 的附加调用。所有权的时期在线程调用 <a href="cpp-thread-recursive_mutex-unlock.html"><code>unlock</code></a> 匹配次数时结束。</li>
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<li>线程占有 <code>recursive_mutex</code> 时，若其他所有线程试图要求 <code>recursive_mutex</code> 的所有权，则它们将阻塞（对于调用 <a href="cpp-thread-recursive_mutex-lock.html"><code>lock</code></a> ）或收到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 返回值（对于调用 <a href="cpp-thread-recursive_mutex-try_lock.html"><code>try_lock</code></a> ）。</li>
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<li>可锁定 <code>recursive_mutex</code> 次数的最大值是未指定的，但抵达该数后，对 <a href="cpp-thread-recursive_mutex-lock.html"><code>lock</code></a> 的调用将抛出 <span class="t-lc"><a href="cpp-error-system_error.html">std::system_error</a></span> 而对 <a href="cpp-thread-mutex-try_lock.html"><code>try_lock</code></a> 的调用将返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</li>
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</ul>
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<p>若 <code>recursive_mutex</code> 在仍为某线程占有时被销毁，则程序行为未定义。 <code>recursive_mutex</code> 类满足<a href="cpp-named_req-Mutex.html"><span style="font-style:italic">互斥体</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Mutex)</span></a> 和<a href="cpp-named_req-StandardLayoutType.html"><span style="font-style:italic">标准布局类型</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(StandardLayoutType)</span></a> 的所有要求。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<td><code>native_handle_type</code><span class="t-mark">(可选)</span></td>
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<td><i>实现定义</i></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-thread-recursive_mutex-recursive_mutex.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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<td>构造互斥<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-thread-recursive_mutex-~recursive_mutex.html"><span class="t-lines"><span>(析构函数)</span></span></a></div>
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</div>
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</td>
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<td>销毁互斥<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>operator=</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[被删除]</span></span></span></div>
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</div>
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<td>不可复制赋值<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h5><span class="mw-headline" id=".E9.94.81.E5.AE.9A">锁定</span></h5>
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<div><a href="cpp-thread-recursive_mutex-lock.html"><span class="t-lines"><span>lock</span></span></a></div>
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<td>锁定互斥，若互斥不可用则阻塞<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-thread-recursive_mutex-try_lock.html"><span class="t-lines"><span>try_lock</span></span></a></div>
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</div>
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</td>
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<td>尝试锁定互斥，若互斥不可用则返回<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-thread-recursive_mutex-unlock.html"><span class="t-lines"><span>unlock</span></span></a></div>
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<td>解锁互斥<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h5><span class="mw-headline" id=".E5.8E.9F.E7.94.9F.E5.8F.A5.E6.9F.84">原生句柄</span></h5>
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<div><a href="cpp-thread-recursive_mutex-native_handle.html"><span class="t-lines"><span>native_handle</span></span></a></div>
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</td>
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<td>返回底层实现定义的原生句柄<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p><code>recursive_mutex</code> 的使用场景之一是保护类中的共享状态，而类的成员函数可能相互调用</p>
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <mutex></span>
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<span class="kw1">class</span> X <span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">recursive_mutex</span> m<span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> shared<span class="sy4">;</span>
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<span class="kw1">public</span><span class="sy4">:</span>
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<span class="kw4">void</span> fun1<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-thread-lock_guard.html"><span class="kw2165">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">recursive_mutex</span><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
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shared <span class="sy1">=</span> <span class="st0">"fun1"</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"in fun1, shared variable is now "</span> <span class="sy1"><<</span> shared <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> fun2<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-thread-lock_guard.html"><span class="kw2165">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">recursive_mutex</span><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
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shared <span class="sy1">=</span> <span class="st0">"fun2"</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"in fun2, shared variable is now "</span> <span class="sy1"><<</span> shared <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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fun1<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 递归锁在此处变得有用</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"back in fun2, shared variable is "</span> <span class="sy1"><<</span> shared <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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X x<span class="sy4">;</span>
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<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span><span class="sy3">&</span>X<span class="sy4">::</span><span class="me2">fun1</span>, <span class="sy3">&</span>x<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> t2<span class="br0">(</span><span class="sy3">&</span>X<span class="sy4">::</span><span class="me2">fun2</span>, <span class="sy3">&</span>x<span class="br0">)</span><span class="sy4">;</span>
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t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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t2.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">in fun1, shared variable is now fun1
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in fun2, shared variable is now fun2
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in fun1, shared variable is now fun1
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back in fun2, shared variable is fun1</pre></div>
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