54 lines
3.0 KiB
HTML
54 lines
3.0 KiB
HTML
<!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::latch::count_down</title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_latch_count_down skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::latch::</span>count_down</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-latch.html">latch</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><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> count_down<span class="br0">(</span> <a href="cpp-types-ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a> n <span class="sy1">=</span> <span class="nu0">1</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>原子地减少内部计数器 <code>n</code> 而不阻塞调用方。</p>
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<p>若 <code>n</code> 大于内部计数器的值或为负，则行为未定义。</p>
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<p>此操作<a href="cpp-atomic-memory_order.html#.E5.BC.BA.E5.85.88.E5.8F.91.E7.94.9F.E4.BA.8E">强先发生于</a>所有于此 <code>latch</code> 上除阻的调用。</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>n</td>
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<td>-</td>
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<td>内部计数器所自减的值</td>
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</table>
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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>错误时抛出 <span class="t-lc"><a href="cpp-error-system_error.html">std::system_error</a></span> ，带有对互斥体类型允许的错误码。</p>
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