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web/cppreference-zh/chmhelp/cpp-thread-mutex-try_lock.html
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web/cppreference-zh/chmhelp/cpp-thread-mutex-try_lock.html
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<!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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::mutex::try_lock</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_mutex_try_lock skin-cppreference2 action-view cpp-page-template 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::mutex::</span>try_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>‎ | <a href="cpp-thread-mutex.html">mutex</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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<div class="t-page-template" style="">
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<p></p>
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</div>
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<table class="t-dcl-begin">
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<tbody>
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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="kw4">bool</span> try_lock<span class="br0">(</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>
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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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</tbody>
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</table>
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<p>尝试锁定互斥。立即返回。成功获得锁时返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<p>允许此函数虚假地失败而返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，即使互斥当前未为任何其他线程所锁定。</p>
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<p>若已占有 <code>mutex</code> 的线程调用 <code>try_lock</code> ，则行为未定义。</p>
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<p>若此操作返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则同一互斥上的先前 <span class="t-lc"><a href="cpp-thread-mutex-unlock.html">unlock()</a></span> 操作<i>同步于</i>（定义于 <span class="t-lc"><a href="cpp-atomic-memory_order.html">std::memory_order</a></span> ）它。注意若此操作返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，则先前的 <span class="t-lc"><a href="cpp-thread-mutex-lock.html">lock()</a></span> 不与之同步。</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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<p>（无）</p>
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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>若成功取得锁则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>不抛出。</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-template-editlink" style=""></div>
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<div class="t-example">
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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 <chrono></span>
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<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> // std::cout</span>
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<a href="cpp-chrono-duration.html"><span class="kw996">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">milliseconds</span></span></a> interval<span class="br0">(</span><span class="nu0">100</span><span class="br0">)</span><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> mutex<span class="sy4">;</span>
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<span class="kw4">int</span> job_shared <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 两个线程都能修改 'job_shared',</span>
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<span class="co1">// mutex 将保护此变量</span>
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<span class="kw4">int</span> job_exclusive <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 只有一个线程能修改 'job_exclusive'</span>
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<span class="co1">// 不需要保护</span>
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<span class="co1">// 此线程能修改 'job_shared' 和 'job_exclusive'</span>
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<span class="kw4">void</span> job_1<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</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>interval<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 令 'job_2' 持锁</span>
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<span class="kw1">while</span> <span class="br0">(</span><span class="kw2">true</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="co1">// 尝试锁定 mutex 以修改 'job_shared'</span>
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<span class="kw1">if</span> <span class="br0">(</span>mutex.<span class="me1">try_lock</span><span class="br0">(</span><span class="br0">)</span><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> <span class="st0">"job shared ("</span> <span class="sy1"><<</span> job_shared <span class="sy1"><<</span> <span class="st0">")<span class="es1">\n</span>"</span><span class="sy4">;</span>
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mutex.<span class="me1">unlock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<span class="co1">// 不能获取锁以修改 'job_shared'</span>
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<span class="co1">// 但有其他工作可做</span>
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<span class="sy2">++</span>job_exclusive<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">"job exclusive ("</span> <span class="sy1"><<</span> job_exclusive <span class="sy1"><<</span> <span class="st0">")<span class="es1">\n</span>"</span><span class="sy4">;</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>interval<span class="br0">)</span><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="br0">}</span>
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<span class="co1">// 此线程只能修改 'job_shared'</span>
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<span class="kw4">void</span> job_2<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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mutex.<span class="me1">lock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</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><span class="nu0">5</span> <span class="sy2">*</span> interval<span class="br0">)</span><span class="sy4">;</span>
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<span class="sy2">++</span>job_shared<span class="sy4">;</span>
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mutex.<span class="me1">unlock</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">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> thread_1<span class="br0">(</span>job_1<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> thread_2<span class="br0">(</span>job_2<span class="br0">)</span><span class="sy4">;</span>
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thread_1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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thread_2.<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">job exclusive (1)
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job exclusive (2)
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job exclusive (3)
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job exclusive (4)
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job shared (1)</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-mutex-lock.html"><span class="t-lines"><span>lock</span></span></a></div>
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</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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</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-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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</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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