58 lines
4.7 KiB
HTML
58 lines
4.7 KiB
HTML
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<title>std::counting_semaphore<LeastMaxValue>::try_acquire_for</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::counting_semaphore<LeastMaxValue>::</span>try_acquire_for</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-counting_semaphore.html">counting semaphore</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> Rep, <span class="kw1">class</span> Period<span class="sy1">></span><br />
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<span class="kw4">bool</span> try_acquire_for<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw993">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">duration</span></span></a><span class="sy1"><</span>Rep, Period<span class="sy1">></span><span class="sy3">&</span> rel_time <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>若内部计数器大于 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 则尝试原子地将它减少 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span> ；否则阻塞直至它大于 ​<span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 且能成功地减少内部计数器，或已经超出 <code>rel_time</code> 时间点。</p>
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<h3><span class="mw-headline" id=".E5.89.8D.E6.9D.A1.E4.BB.B6">前条件</span></h3>
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<p>（无）</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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<td>rel_time</td>
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<td>-</td>
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<td>函数必须为失败等待到的<i>最小</i>时长</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>若减少内部计数器则为 <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>可能抛出 <span class="t-lc"><a href="cpp-error-system_error.html">std::system_error</a></span> 或与到达时间相关的异常。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>实践中函数可能需要经过长于 <code>rel_time</code> 的时间才失败。</p>
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<p>允许实现未能减少计数器，即使它大于 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ——即允许它们虚假地失败并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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