182 lines
19 KiB
HTML
182 lines
19 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::lock</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_lock skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>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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<td>
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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>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx11">
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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> Lockable1, <span class="kw1">class</span> Lockable2, <span class="kw1">class</span>... <span class="me1">LockableN</span> <span class="sy1">></span><br />
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<span class="kw4">void</span> lock<span class="br0">(</span> Lockable1<span class="sy3">&</span> lock1, Lockable2<span class="sy3">&</span> lock2, LockableN<span class="sy3">&</span>... <span class="me1">lockn</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p>锁定给定的<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> 对象 <code>lock1</code> 、 <code>lock2</code> 、 <code>...</code> 、 <code>lockn</code> ，用免死锁算法避免死锁。</p>
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<p>以对 <code>lock</code> 、 <code>try_lock</code> 和 <code>unlock</code> 的未指定系列调用锁定对象。若调用 <code>lock</code> 或 <code>unlock</code> 导致异常，则在重抛前对任何已锁的对象调用 <code>unlock</code> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>lock1, lock2, ... , lockn</td>
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<td>-</td>
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<td>要锁定的<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> 对象</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>（无）</p>
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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><a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/release/doc/html/thread/synchronization.html#thread.synchronization.lock_functions.lock_range">Boost 提供此函数的一个版本</a>，它接收以一对迭代器定义的<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> 对象序列。</p>
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<p><a href="cpp-thread-scoped_lock.html"><tt>std::scoped_lock</tt></a> 提供此函数的 <a href="cpp-language-raii.html">RAII</a> 包装，通常它比裸调用 <code>std::lock</code> 更好。</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>下列示例用 <code>std::lock</code> 锁定互斥对，而不死锁。</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="co1">// 用 std::lock 获得二个锁，而不担心对 assign_lunch_partner 的其他调用会死锁我们</span>
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<span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">lock</span><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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<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> lk1<span class="br0">(</span>e1.<span class="me1">m</span>, <a href="cpp-thread-lock_tag.html"><span class="kw2165">std::<span class="me2">adopt_lock</span></span></a><span class="br0">)</span><span class="sy4">;</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> lk2<span class="br0">(</span>e2.<span class="me1">m</span>, <a href="cpp-thread-lock_tag.html"><span class="kw2165">std::<span class="me2">adopt_lock</span></span></a><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 等价代码（若需要 unique_locks ，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="co1">// C++17 中可用的较优解法</span>
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<span class="co1">// std::scoped_lock lk(e1.m, e2.m);</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">// 在平行线程指派，因为发邮件给用户告知午餐指派，会消耗长时间</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 bob got locks
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christina and alice are waiting for locks
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christina and alice got 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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Employee alice has lunch partners: bob christina
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Employee bob has lunch partners: alice christina dave
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Employee christina has lunch partners: bob alice
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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=".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-try_lock.html"><span class="t-lines"><span>try_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>试图通过重复调用 <code>try_lock</code> 获得互斥体的所有权<br />
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<span class="t-mark">(函数模板)</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><a href="cpp-thread-scoped_lock.html"><span class="t-lines"><span>scoped_lock</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>用于多个互斥体的免死锁 RAII 封装器<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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</body>
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