191 lines
13 KiB
HTML
191 lines
13 KiB
HTML
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<title>std::mutex</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_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>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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> mutex<span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p><code>mutex</code> 类是能用于保护共享数据免受从多个线程同时访问的同步原语。</p>
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<p><code>mutex</code> 提供排他性非递归所有权语义：</p>
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<ul>
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<li>调用方线程从它成功调用 <a href="cpp-thread-mutex-lock.html"><code>lock</code></a> 或 <a href="cpp-thread-mutex-try_lock.html"><code>try_lock</code></a> 开始，到它调用 <a href="cpp-thread-mutex-unlock.html"><code>unlock</code></a> 为止<i>占有</i> <code>mutex</code> 。</li>
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<li>线程占有 <code>mutex</code> 时，所有其他线程若试图要求 <code>mutex</code> 的所有权，则将阻塞（对于 <a href="cpp-thread-mutex-lock.html"><code>lock</code></a> 的调用）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 <a href="cpp-thread-mutex-try_lock.html"><code>try_lock</code></a> ）.</li>
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<li>调用方线程在调用 <a href="cpp-thread-mutex-lock.html"><code>lock</code></a> 或 <a href="cpp-thread-mutex-try_lock.html"><code>try_lock</code></a> 前必须不占有 <code>mutex</code> 。</li>
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</ul>
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<p>若 <code>mutex</code> 在仍为任何线程所占有时即被销毁，或在占有 <code>mutex</code> 时线程终止，则行为未定义。 <code>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> 的全部要求。</p>
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<p><code>std::mutex</code> 既不可复制亦不可移动。</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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<table class="t-dsc-begin">
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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-mutex-mutex.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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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-mutex-~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 class="t-dsc-member-div">
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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>
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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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<td colspan="2">
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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 class="t-dsc-member-div">
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<div><a href="cpp-thread-mutex-lock.html"><span class="t-lines"><span>lock</span></span></a></div>
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</td>
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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-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 class="t-dsc-member-div">
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<div><a href="cpp-thread-mutex-unlock.html"><span class="t-lines"><span>unlock</span></span></a></div>
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</div>
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</td>
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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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<td colspan="2">
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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-mutex-native_handle.html"><span class="t-lines"><span>native_handle</span></span></a></div>
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</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=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>通常不直接使用 <code>std::mutex</code> ： <span class="t-lc"><a href="cpp-thread-unique_lock.html">std::unique_lock</a></span> 、 <span class="t-lc"><a href="cpp-thread-lock_guard.html">std::lock_guard</a></span> <span class="t-rev-inl t-since-cxx17"><span>或 <span class="t-lc">std::scoped_lock</span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>以更加异常安全的方式管理锁定。</p>
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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>此示例展示 <code>mutex</code> 能如何用于在保护共享于二个线程间的 <span class="t-lc"><a href="cpp-container-map.html">std::map</a></span> 。</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 <map></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <chrono></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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<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> g_pages<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">mutex</span> g_pages_mutex<span class="sy4">;</span>
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<span class="kw4">void</span> save_page<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> <span class="sy3">&</span>url<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co1">// 模拟长页面读取</span>
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<a href="cpp-thread-sleep_for.html"><span class="kw2149">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="br0">)</span><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> result <span class="sy1">=</span> <span class="st0">"fake content"</span><span class="sy4">;</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">mutex</span><span class="sy1">></span> guard<span class="br0">(</span>g_pages_mutex<span class="br0">)</span><span class="sy4">;</span>
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g_pages<span class="br0">[</span>url<span class="br0">]</span> <span class="sy1">=</span> result<span class="sy4">;</span>
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<span class="br0">}</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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<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span>save_page, <span class="st0">"http://foo"</span><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>save_page, <span class="st0">"http://bar"</span><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="co1">// 现在访问g_pages是安全的，因为线程t1/t2生命周期已结束</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span> <span class="sy3">&</span>pair <span class="sy4">:</span> g_pages<span class="br0">)</span> <span class="br0">{</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> pair.<span class="me1">first</span> <span class="sy1"><<</span> <span class="st0">" => "</span> <span class="sy1"><<</span> pair.<span class="me1">second</span> <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="br0">}</span></pre></div>
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</div>
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<p>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">http://bar => fake content
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http://foo => fake content</pre></div>
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