283 lines
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283 lines
22 KiB
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<title>std::atomic_fetch_or, std::atomic_fetch_or_explicit</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>atomic_fetch_or, <span style="font-size:0.7em; line-height:130%">std::</span>atomic_fetch_or_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></td>
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<td rowspan="142">(1)</td>
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<td rowspan="142"><span class="t-mark-rev t-since-cxx11">(C++11 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>T atomic_fetch_or<span class="br0">(</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> obj,<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> arg <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>T atomic_fetch_or<span class="br0">(</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> obj,<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> arg <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-cxx11">(C++11 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>T atomic_fetch_or_explicit<span class="br0">(</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> obj,<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> arg,<br /></p>
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<a href="cpp-atomic-memory_order.html"><span class="kw2090">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>T atomic_fetch_or_explicit<span class="br0">(</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> obj,<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> arg,<br /></p>
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<a href="cpp-atomic-memory_order.html"><span class="kw2090">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>原子地以 <code>obj</code> 的旧值和 <code>arg</code> 逐位或的结果替换 <code>obj</code> 所指向的值。返回 <code>obj</code> 先前保有的值。</p>
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<p>如同执行下列内容一般进行运算：</p>
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<div class="t-li1"><span class="t-li">1)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">obj<span class="sy2">-</span><span class="sy1">></span>fetch_or<span class="br0">(</span>arg<span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">obj<span class="sy2">-</span><span class="sy1">></span>fetch_or<span class="br0">(</span>arg, order<span class="br0">)</span></span></span></div>
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<p>若 <code>std::atomic<T></code> 无 <code>fetch_or</code> 成员（此成员仅对<a href="cpp-atomic-atomic.html#.E5.AF.B9.E6.95.B4.E6.95.B0.E7.B1.BB.E5.9E.8B.E7.9A.84.E7.89.B9.E5.8C.96">整数类型</a>提供），则程序为病式。</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>obj</td>
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<td>-</td>
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<td>指向要修改的原子对象的指针</td>
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<tr class="t-par">
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<td>arg</td>
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<td>-</td>
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<td>要与原子对象中的值逐位或的值</td>
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</tr>
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<tr class="t-par">
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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：容许所有值。</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><code>*obj</code> 的<a href="cpp-atomic-memory_order.html#.E4.BF.AE.E6.94.B9.E9.A1.BA.E5.BA.8F">修改顺序</a>中立即前趋此函数效果的值。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span>
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T atomic_fetch_or<span class="br0">(</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> obj, <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> arg <span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> obj<span class="sy2">-</span><span class="sy1">></span>fetch_or<span class="br0">(</span>arg<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=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-template-editlink" style=""></div>
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<div class="t-example">
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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 <atomic></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <chrono></span>
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<span class="co2">#include <functional></span>
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<span class="co1">// 仅为演示目的的二元信号量</span>
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<span class="co1">// 此乃简单却有意义的示例：若无线程则原子操作为不必要。 </span>
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<span class="kw1">class</span> Semaphore <span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">atomic_char</span> m_signaled<span class="sy4">;</span>
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<span class="kw1">public</span><span class="sy4">:</span>
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Semaphore<span class="br0">(</span><span class="kw4">bool</span> initial <span class="sy1">=</span> <span class="kw2">false</span><span class="br0">)</span>
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<span class="br0">{</span>
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m_signaled <span class="sy1">=</span> initial<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 阻塞直至信号量被发信</span>
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<span class="kw4">void</span> take<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">while</span> <span class="br0">(</span><span class="sy3">!</span><a href="cpp-atomic-atomic_fetch_sub.html"><span class="kw2082">std::<span class="me2">atomic_fetch_and</span></span></a><span class="br0">(</span><span class="sy3">&</span>m_signaled, <span class="kw2">false</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-thread-sleep_for.html"><span class="kw2147">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw996">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">milliseconds</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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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> put<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">atomic_fetch_or</span><span class="br0">(</span><span class="sy3">&</span>m_signaled, <span class="kw2">true</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">class</span> ThreadedCounter <span class="br0">{</span>
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<span class="kw4">static</span> <span class="kw4">const</span> <span class="kw4">int</span> N <span class="sy1">=</span> <span class="nu0">100</span><span class="sy4">;</span>
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<span class="kw4">static</span> <span class="kw4">const</span> <span class="kw4">int</span> REPORT_INTERVAL <span class="sy1">=</span> <span class="nu0">10</span><span class="sy4">;</span>
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<span class="kw4">int</span> m_count<span class="sy4">;</span>
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<span class="kw4">bool</span> m_done<span class="sy4">;</span>
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Semaphore m_count_sem<span class="sy4">;</span>
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Semaphore m_print_sem<span class="sy4">;</span>
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<span class="kw4">void</span> count_up<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span>m_count <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> m_count <span class="sy1"><=</span> N<span class="sy4">;</span> m_count<span class="sy2">++</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>m_count <span class="sy2">%</span> REPORT_INTERVAL <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>m_count <span class="sy1">==</span> N<span class="br0">)</span> m_done <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
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m_print_sem.<span class="me1">put</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 对打印发信，使之发生</span>
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m_count_sem.<span class="me1">take</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等待直至打印完成进展</span>
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<span class="br0">}</span>
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<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">"count_up() done<span class="es1">\n</span>"</span><span class="sy4">;</span>
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m_done <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
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m_print_sem.<span class="me1">put</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> print_count<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">do</span> <span class="br0">{</span>
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m_print_sem.<span class="me1">take</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> m_count <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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m_count_sem.<span class="me1">put</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">while</span> <span class="br0">(</span><span class="sy3">!</span>m_done<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">"print_count() done<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">public</span><span class="sy4">:</span>
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ThreadedCounter<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> m_done<span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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<span class="kw4">void</span> run<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> print_thread <span class="sy1">=</span> <a href="cpp-thread-thread.html"><span class="kw2144">std::<span class="me2">thread</span></span></a><span class="br0">(</span><span class="sy3">&</span>ThreadedCounter<span class="sy4">::</span><span class="me2">print_count</span>, this<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">auto</span> count_thread <span class="sy1">=</span> <a href="cpp-thread-thread.html"><span class="kw2144">std::<span class="me2">thread</span></span></a><span class="br0">(</span><span class="sy3">&</span>ThreadedCounter<span class="sy4">::</span><span class="me2">count_up</span>, this<span class="br0">)</span><span class="sy4">;</span>
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print_thread.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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count_thread.<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>
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<span class="br0">}</span><span class="sy4">;</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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ThreadedCounter m_counter<span class="sy4">;</span>
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m_counter.<span class="me1">run</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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</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">10
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20
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30
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40
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50
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60
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70
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80
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90
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100
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print_count() done
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count_up() done</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P0558R1">P0558R1</a></td>
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<td>C++11</td>
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<td>曾要求准确类型匹配，因为从多个参数推导 <code>T</code></td>
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<td>仅从 <code>atomic</code> 参数推导 <code>T</code></td>
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</tr>
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</table>
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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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<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-atomic-atomic-fetch_or.html"><span class="t-lines"><span>fetch_or</span></span></a></div>
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</div>
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</td>
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<td>原子地进行参数和原子对象的值的逐位或，并获得先前保有的值<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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</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-atomic-atomic_fetch_and.html"><span class="t-lines"><span>atomic_fetch_and</span><span>atomic_fetch_and_explicit</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>将原子对象替换为与非原子实参逻辑与的结果，并获得原子对象的先前值<br />
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<span class="t-mark">(函数模板)</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-atomic-atomic_fetch_xor.html"><span class="t-lines"><span>atomic_fetch_xor</span><span>atomic_fetch_xor_explicit</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>将原子对象替换为与非原子实参逻辑异或的结果，并获得原子对象的先前值<br />
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<span class="t-mark">(函数模板)</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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</div>
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</div>
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</div>
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</body>
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