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<title>std::shared_timed_mutex::lock</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::shared_timed_mutex::</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>‎ | <a href="cpp-thread-shared_timed_mutex.html">shared timed mutex</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> lock<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<p>锁定互斥。若另一线程已锁定互斥，则到 <code>lock</code> 的调用将阻塞执行，直至获得锁。</p>
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<p>若已以任何模式（共享或排他性）占有 <code>mutex</code> 的线程调用 <code>lock</code> ，则行为未定义。</p>
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<p>同一互斥上先前的 <span class="t-lc"><a href="cpp-thread-shared_timed_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> ）此操作。</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>（无）</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>错误发生时抛出 <span class="t-lc"><a href="cpp-error-system_error.html">std::system_error</a></span> ，包括底层操作系统阻止 <code>lock</code> 满足其规定的错误。在抛出任何异常的情况下，不锁定互斥。</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>通常不直接调用 <code>lock()</code> ：用 <span class="t-lc"><a href="cpp-thread-unique_lock.html">std::unique_lock</a></span> 与 <span class="t-lc"><a href="cpp-thread-lock_guard.html">std::lock_guard</a></span> 管理排他性锁定。</p>
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<p>共享互斥不支持直接从共享到唯一所有权模式的迁移：必须在以 <code>lock()</code> 获得排他性所有权之前用 <span class="t-lc"><a href="cpp-thread-shared_timed_mutex-unlock_shared.html">unlock_shared()</a></span> 交出共享锁。可为此目的使用 <a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/release/doc/html/thread/synchronization.html#thread.synchronization.mutex_types.upgrade_mutex">boost::upgrade_mutex</a> 。</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>此示例演示 <code>lock</code> 与 <code>unlock</code> 能如何用于保护共享数据。</p>
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<div class="t-example-live-link"></div>
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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 <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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<span class="kw4">int</span> g_num <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 为 g_num_mutex 所保护</span>
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<a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> g_num_mutex<span class="sy4">;</span>
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<span class="kw4">void</span> slow_increment<span class="br0">(</span><span class="kw4">int</span> id<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">3</span><span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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g_num_mutex.<span class="me1">lock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="sy2">++</span>g_num<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> id <span class="sy1"><<</span> <span class="st0">" => "</span> <span class="sy1"><<</span> g_num <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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g_num_mutex.<span class="me1">unlock</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><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="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>slow_increment, <span class="nu0">0</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>slow_increment, <span class="nu0">1</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="br0">}</span></pre></div>
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<p>可能的输出：</p>
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<pre class="de1">0 => 1
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1 => 2
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0 => 3
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1 => 4
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0 => 5
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1 => 6</pre></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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<div><a href="cpp-thread-shared_timed_mutex-try_lock.html"><span class="t-lines"><span>try_lock</span></span></a></div>
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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-shared_timed_mutex-unlock.html"><span class="t-lines"><span>unlock</span></span></a></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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