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130 lines
12 KiB
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<title>std::recursive_timed_mutex::try_lock_until</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_recursive_timed_mutex_try_lock_until 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_timed_mutex::</span>try_lock_until</h1>
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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_timed_mutex.html">recursive timed mutex</a></span></div>
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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> Clock, <span class="kw1">class</span> Duration <span class="sy1">></span><br />
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<span class="kw4">bool</span> try_lock_until<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-time_point.html"><span class="kw991">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">time_point</span></span></a><span class="sy1"><</span>Clock,Duration<span class="sy1">></span><span class="sy3">&</span> timeout_time <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>尝试所互斥。阻塞直至抵达指定的 <code>timeout_time</code> 或得到锁，取决于何者先到来。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>若已经过 <code>timeout_time</code> ，则此函数表现同 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-try_lock.html">try_lock()</a></span> 。</p>
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<p><code>Clock</code> 必须符合<a href="cpp-named_req-Clock.html"><span style="font-style:italic">时钟</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Clock)</span></a> 要求。<span class="t-rev-inl t-since-cxx20"><span>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">is_clock_v</span><span class="sy1"><</span>Clock<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则程序为非良构。</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span></p>
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<p>标准推荐使用绑定到 <code>timeout_time</code> 的时钟，该情况下可以计入时钟的调整。从而在调用时刻，阻塞的时长可以，但也可以不，小于或大于 <span class="t-c"><span class="mw-geshi cpp source-cpp">timeout_time <span class="sy2">-</span> Clock<span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span></span></span> 。这取决于调整的方向以及实现是否尊重它。函数亦可能由于调度或资源纠纷延迟，而阻塞长于到抵达 <code>timeout_time</code> 之后。</p>
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<p>同 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-try_lock.html">try_lock()</a></span> ，允许此函数虚假地失败并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，即使在 <code>timeout_time</code> 前的某点任何线程都不锁定互斥。</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> ，则同一互斥上先前的 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-unlock.html">unlock()</a></span> 调用<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。</p>
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<p>线程可以在递归互斥上重复调用 <code>try_lock_until</code> 。对 <code>try_lock_until</code> 的成功调用增加所有权计数：仅在线程调用 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-unlock.html">unlock</a></span> 匹配次数后才会释放互斥。</p>
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<p>所有权等级数的最大值是未指定的。若超出此值，则到 <code>try_lock_until</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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<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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<td>timeout_time</td>
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<td>-</td>
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<td>要阻塞到的最大时间点</td>
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</tr>
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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>若成功获得锁则为 <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>执行期间时钟、时间点或时长可能抛出的异常（标准库提供的时钟、时间点和时长决不抛出）</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">
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<p>此示例展示 10 秒的阻塞</p>
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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 <thread></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <chrono></span>
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<span class="co2">#include <mutex></span>
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<a href="cpp-thread-recursive_timed_mutex.html"><span class="kw2157">std::<span class="me2">recursive_timed_mutex</span></span></a> test_mutex<span class="sy4">;</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> now<span class="sy1">=</span>std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">steady_clock</span><span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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test_mutex.<span class="me1">try_lock_until</span><span class="br0">(</span>now <span class="sy2">+</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">10</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> <span class="st0">"hello world<span class="es1">\n</span>"</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-lock_guard.html"><span class="kw2166">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="cpp-thread-recursive_timed_mutex.html"><span class="kw2157">std::<span class="me2">recursive_timed_mutex</span></span></a><span class="sy1">></span> l<span class="br0">(</span>test_mutex<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> t<span class="br0">(</span>f<span class="br0">)</span><span class="sy4">;</span>
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t.<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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<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_timed_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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_mutex-try_lock.html"><span class="t-lines"><span>try_lock</span></span></a></div>
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</div>
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</td>
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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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</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-recursive_timed_mutex-try_lock_for.html"><span class="t-lines"><span>try_lock_for</span></span></a></div>
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</div>
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</td>
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<td>尝试锁定互斥，若互斥在指定的时限时期中不可用则返回<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_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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