244 lines
21 KiB
HTML
244 lines
21 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::scoped_lock</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_scoped_lock 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>scoped_lock</h1>
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<div id="bodyContent">
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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 id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span>... <span class="me1">MutexTypes</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> scoped_lock<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-cxx17">(C++17 起)</span></td>
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<p>类 <code>scoped_lock</code> 是提供便利 <a href="https://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization" class="extiw" title="enwiki:Resource Acquisition Is Initialization">RAII 风格</a>机制的互斥包装器,它在作用域块的存在期间占有一或多个互斥。</p>
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<p>创建 <code>scoped_lock</code> 对象时,它试图取得给定互斥的所有权。控制离开创建 <code>scoped_lock</code> 对象的作用域时,析构 <code>scoped_lock</code> 并释放互斥。若给出数个互斥,则使用免死锁算法,如同以 <span class="t-lc"><a href="cpp-thread-lock.html">std::lock</a></span> 。</p>
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<p><code>scoped_lock</code> 类不可复制。</p>
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<h3><span class="mw-headline" id=".E6.A8.A1.E6.9D.BF.E5.BD.A2.E5.8F.82">模板形参</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>MutexTypes</td>
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<td>-</td>
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<td>要锁定的互斥类型。类型必须满足<a href="cpp-named_req-Lockable.html"><span style="font-style:italic">可锁定</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Lockable)</span></a> 要求,除非 <span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof...<span class="br0">(</span>MutexTypes<span class="br0">)</span><span class="sy1">==</span><span class="nu0">1</span></span></span> ,该情况下唯一的类型必须满足<a href="cpp-named_req-BasicLockable.html"><span style="font-style:italic">基本可锁定</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(BasicLockable)</span></a></td>
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</table>
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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>mutex_type</code> <span class="t-mark">(若 <code>sizeof...(MutexTypes)==1</code>)</span></td>
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<td><code>Mutex</code> , <code>MutexTypes...</code> 中的单独类型</td>
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</table>
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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-scoped_lock-scoped_lock.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 scoped_lock ,可选地锁定给定的互斥<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-scoped_lock-~scoped_lock.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>析构 scoped_lock 对象,解锁底层互斥<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<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<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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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>以下示例用 <code>std::scoped_lock</code> 锁定互斥对而不死锁,且为 RAII 风格。</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 <mutex></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <functional></span>
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<span class="co2">#include <chrono></span>
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<span class="co2">#include <string></span>
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<span class="kw1">struct</span> Employee <span class="br0">{</span>
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Employee<span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> id<span class="br0">)</span> <span class="sy4">:</span> id<span class="br0">(</span>id<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> id<span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</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><span class="sy1">></span> lunch_partners<span class="sy4">;</span>
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<a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> 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> output<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> ret <span class="sy1">=</span> <span class="st0">"Employee "</span> <span class="sy2">+</span> id <span class="sy2">+</span> <span class="st0">" has lunch partners: "</span><span class="sy4">;</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> partner <span class="sy4">:</span> lunch_partners <span class="br0">)</span>
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ret <span class="sy2">+</span><span class="sy1">=</span> partner <span class="sy2">+</span> <span class="st0">" "</span><span class="sy4">;</span>
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<span class="kw1">return</span> ret<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">void</span> send_mail<span class="br0">(</span>Employee <span class="sy3">&</span>, Employee <span class="sy3">&</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co1">// 模拟耗时的发信操作</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">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> assign_lunch_partner<span class="br0">(</span>Employee <span class="sy3">&</span>e1, Employee <span class="sy3">&</span>e2<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">static</span> <a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> io_mutex<span class="sy4">;</span>
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<span class="br0">{</span>
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<a href="cpp-thread-lock_guard.html"><span class="kw2166">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>io_mutex<span class="br0">)</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> e1.<span class="me1">id</span> <span class="sy1"><<</span> <span class="st0">" and "</span> <span class="sy1"><<</span> e2.<span class="me1">id</span> <span class="sy1"><<</span> <span class="st0">" are waiting for locks"</span> <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">{</span>
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<span class="co1">// 用 std::scoped_lock 取得二个锁,而无需担心</span>
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<span class="co1">// 其他对 assign_lunch_partner 的调用死锁我们</span>
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<span class="co1">// 而且它亦提供便利的 RAII 风格机制</span>
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std<span class="sy4">::</span><span class="me2">scoped_lock</span> lock<span class="br0">(</span>e1.<span class="me1">m</span>, e2.<span class="me1">m</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 等价代码 1 (用 std::lock 和 std::lock_guard )</span>
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<span class="co1">// std::lock(e1.m, e2.m);</span>
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<span class="co1">// std::lock_guard<std::mutex> lk1(e1.m, std::adopt_lock);</span>
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<span class="co1">// std::lock_guard<std::mutex> lk2(e2.m, std::adopt_lock);</span>
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<span class="co1">// 等价代码 2 (若需要 unique_lock ,例如对于条件变量)</span>
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<span class="co1">// std::unique_lock<std::mutex> lk1(e1.m, std::defer_lock);</span>
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<span class="co1">// std::unique_lock<std::mutex> lk2(e2.m, std::defer_lock);</span>
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<span class="co1">// std::lock(lk1, lk2);</span>
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<span class="br0">{</span>
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<a href="cpp-thread-lock_guard.html"><span class="kw2166">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>io_mutex<span class="br0">)</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> e1.<span class="me1">id</span> <span class="sy1"><<</span> <span class="st0">" and "</span> <span class="sy1"><<</span> e2.<span class="me1">id</span> <span class="sy1"><<</span> <span class="st0">" got locks"</span> <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span>
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<span class="br0">}</span>
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e1.<span class="me1">lunch_partners</span>.<span class="me1">push_back</span><span class="br0">(</span>e2.<span class="me1">id</span><span class="br0">)</span><span class="sy4">;</span>
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e2.<span class="me1">lunch_partners</span>.<span class="me1">push_back</span><span class="br0">(</span>e1.<span class="me1">id</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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send_mail<span class="br0">(</span>e1, e2<span class="br0">)</span><span class="sy4">;</span>
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send_mail<span class="br0">(</span>e2, e1<span class="br0">)</span><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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Employee alice<span class="br0">(</span><span class="st0">"alice"</span><span class="br0">)</span>, bob<span class="br0">(</span><span class="st0">"bob"</span><span class="br0">)</span>, christina<span class="br0">(</span><span class="st0">"christina"</span><span class="br0">)</span>, dave<span class="br0">(</span><span class="st0">"dave"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 在并行线程中指派,因为就午餐指派发邮件消耗很长时间</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="sy1">></span> threads<span class="sy4">;</span>
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threads.<span class="me1">emplace_back</span><span class="br0">(</span>assign_lunch_partner, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>alice<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>bob<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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threads.<span class="me1">emplace_back</span><span class="br0">(</span>assign_lunch_partner, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>christina<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>bob<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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threads.<span class="me1">emplace_back</span><span class="br0">(</span>assign_lunch_partner, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>christina<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>alice<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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threads.<span class="me1">emplace_back</span><span class="br0">(</span>assign_lunch_partner, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>dave<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>bob<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> <span class="sy3">&</span>thread <span class="sy4">:</span> threads<span class="br0">)</span> thread.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</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> alice.<span class="me1">output</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span> <span class="sy1"><<</span> bob.<span class="me1">output</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> christina.<span class="me1">output</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span> <span class="sy1"><<</span> dave.<span class="me1">output</span><span class="br0">(</span><span class="br0">)</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></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">alice and bob are waiting for locks
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alice and bob got locks
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christina and bob are waiting for locks
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christina and alice are waiting for locks
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dave and bob are waiting for locks
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dave and bob got locks
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christina and alice got locks
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christina and bob got locks
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Employee alice has lunch partners: bob christina
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Employee bob has lunch partners: alice dave christina
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Employee christina has lunch partners: alice bob
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Employee dave has lunch partners: bob</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2981">LWG 2981</a></td>
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<td>C++17</td>
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<td>曾提供来自 <code>scoped_lock<MutexTypes...></code> 的冗余推导指引</td>
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<td>已移除</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-unique_lock.html"><span class="t-lines"><span>unique_lock</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>实现可移动的互斥体所有权包装器<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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</table>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-lock_guard.html"><span class="t-lines"><span>lock_guard</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>实现严格基于作用域的互斥体所有权包装器<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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