109 lines
8.3 KiB
HTML
109 lines
8.3 KiB
HTML
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<title>std::recursive_mutex::try_lock</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_recursive_mutex_try_lock skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::recursive_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-recursive_mutex.html">recursive 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><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><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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>线程可以重复调用 <code>try_lock</code> 。到 <code>try_lock</code> 的成功调用自增所有权计数：线程调用 <span class="t-lc"><a href="cpp-thread-recursive_mutex-unlock.html">unlock</a></span> 匹配次数后互斥才会得到释放。</p>
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<p>所有权层数的最大值是未指定的。若超出此数，则到 <code>try_lock</code> 的调用将返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<p>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-recursive_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-recursive_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-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 <mutex></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-recursive_mutex.html"><span class="kw2155">std::<span class="me2">recursive_mutex</span></span></a> test<span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>test.<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">"lock acquired<span class="es1">\n</span>"</span><span class="sy4">;</span>
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test.<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> <span class="kw1">else</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">"lock not acquired<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 现在非递归互斥将从 try_lock 返回 false</span>
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<span class="kw1">if</span> <span class="br0">(</span>test.<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">"lock acquired<span class="es1">\n</span>"</span><span class="sy4">;</span>
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test.<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> <span class="kw1">else</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">"lock not acquired<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">lock acquired
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lock acquired</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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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_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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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_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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