181 lines
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181 lines
13 KiB
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<title>std::atomic_wait, std::atomic_wait_explicit</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>atomic_wait, <span style="font-size:0.7em; line-height:130%">std::</span>atomic_wait_explicit</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-atomic.html">atomic</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-atomic.html"><atomic></a></code></div>
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<td rowspan="142">(1)</td>
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<td rowspan="142"><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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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> T <span class="sy1">></span><br /></span>
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<p><span class="kw4">void</span> atomic_wait<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy2">*</span> object,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span> old <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</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> T <span class="sy1">></span><br /></span>
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<p><span class="kw4">void</span> atomic_wait<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">volatile</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy2">*</span> object,<br /></p>
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<span class="kw1">typename</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span> old <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></div>
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<tbody></tbody>
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<td rowspan="142">(2)</td>
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<td rowspan="142"><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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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> T <span class="sy1">></span><br /></span>
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<p><span class="kw4">void</span> atomic_wait_explicit<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy2">*</span> object,<br />
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<span class="kw1">typename</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span> old,<br /></p>
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</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> T <span class="sy1">></span><br /></span>
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<p><span class="kw4">void</span> atomic_wait_explicit<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">volatile</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy2">*</span> object,<br />
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<span class="kw1">typename</span> <a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span> old,<br /></p>
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></div>
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<p>进行原子等待操作。表现为重复进行下列步骤:</p>
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<ul>
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<li>比较 <span class="t-c"><span class="mw-geshi cpp source-cpp">object<span class="sy2">-</span><span class="sy1">></span>load<span class="br0">(</span><a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a><span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">object<span class="sy2">-</span><span class="sy1">></span>load<span class="br0">(</span>order<span class="br0">)</span></span></span> 与 <code>old</code> 的<a href="cpp-language-object.html">值表示</a>。
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<li>若它们逐位相等则阻塞直至 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 被 <span class="t-lc">std::atomic::notify_one()</span> 或 <span class="t-lc">std::atomic::notify_all()</span> 提醒,或线程被虚假地除阻。</li>
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<li>否则返回。</li>
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<p>允许这些函数虚假地除阻,即由于值更改或提醒之外的原因返回。</p>
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<div class="t-li1"><span class="t-li">1)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">object<span class="sy2">-</span><span class="sy1">></span>wait<span class="br0">(</span>old, <a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">object<span class="sy2">-</span><span class="sy1">></span>wait<span class="br0">(</span>old, order<span class="br0">)</span></span></span> 。</div>
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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>object</td>
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<td>-</td>
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<td>指向要检查并在其上等待的原子对象的指针</td>
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<td>old</td>
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<td>-</td>
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<td>要检测的原子对象不再含有的值</td>
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<td>order</td>
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<td>-</td>
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<td>此操作所用的内存同步顺序:必须不是 <span class="t-lc">std::memory_order::release</span> 或 <span class="t-lc">std::memory_order::acq_rel</span></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>(无)</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>更改检测的这种形式通常比简单轮询或纯自旋锁高效。</p>
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<p>由于 <a rel="nofollow" class="external text" href="https://en.wikipedia.org/wiki/ABA_problem">ABA 问题</a>,可能错失从 <code>old</code> 到另一值再回到 <code>old</code> 的更改,而不除阻。</p>
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<p>比较是逐位的(类似 <span class="t-lc"><a href="cpp-string-byte-memcpy.html">std::memcpy</a></span> );不使用比较运算符。忽略决不参与对象值表示的填充位。</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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<td class="mbox-text" style="">本节未完成<br />
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原因:暂无示例</td>
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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-atomic-atomic-notify_one.html"><span class="t-lines"><span>notify_one</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>提醒至少一个在原子对象上的等待中阻塞的线程<br />
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<span class="t-mark">(<code>std::atomic<T></code> 的公开成员函数)</span></td>
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<div><a href="cpp-atomic-atomic-notify_all.html"><span class="t-lines"><span>notify_all</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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<td>提醒所有在原子对象上的等待中阻塞的线程<br />
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<span class="t-mark">(<code>std::atomic<T></code> 的公开成员函数)</span></td>
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<div><a href="cpp-atomic-atomic_notify_one.html"><span class="t-lines"><span>atomic_notify_one</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>提醒一个在 <code>atomic_wait</code> 中阻塞的线程<br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="cpp-atomic-atomic_notify_all.html"><span class="t-lines"><span>atomic_notify_all</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>提醒所有在 <code>atomic_wait</code> 中阻塞的线程<br />
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<span class="t-mark">(函数模板)</span></td>
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