239 lines
14 KiB
HTML
239 lines
14 KiB
HTML
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<title>std::atomic_flag_test_and_set, std::atomic_flag_test_and_set_explicit</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_atomic_atomic_flag_test_and_set skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>atomic_flag_test_and_set, <span style="font-size:0.7em; line-height:130%">std::</span>atomic_flag_test_and_set_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></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="kw4">bool</span> atomic_flag_test_and_set<span class="br0">(</span> <span class="kw4">volatile</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> atomic_flag_test_and_set<span class="br0">(</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<tbody></tbody>
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<td></td>
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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="kw4">bool</span> atomic_flag_test_and_set_explicit<span class="br0">(</span> <span class="kw4">volatile</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p,<br />
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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></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> atomic_flag_test_and_set_explicit<span class="br0">(</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p,<br />
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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></span></div>
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<p>原子地更改 <code>p</code> 所指向的 <span class="t-lc"><a href="cpp-atomic-atomic_flag.html">std::atomic_flag</a></span> 的状态为设置( <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ),并返回其先前所保有的值。</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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<tr class="t-par">
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<td>p</td>
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<td>-</td>
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<td>指向要访问的 <span class="t-lc"><a href="cpp-atomic-atomic_flag.html">std::atomic_flag</a></span> 的指针</td>
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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</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>p</code> 所指向的标志先前保有的值</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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<table class="eq-fun-cpp-table">
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<th>版本一</th>
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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="kw4">bool</span> atomic_flag_test_and_set<span class="br0">(</span><span class="kw4">volatile</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> p<span class="sy2">-</span><span class="sy1">></span>test_and_set<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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<th>版本二</th>
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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="kw4">bool</span> atomic_flag_test_and_set<span class="br0">(</span><a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> p<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> p<span class="sy2">-</span><span class="sy1">></span>test_and_set<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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<th>版本三</th>
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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="kw4">bool</span> atomic_flag_test_and_set_explicit<span class="br0">(</span><span class="kw4">volatile</span> <a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> 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>
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<span class="br0">{</span>
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<span class="kw1">return</span> p<span class="sy2">-</span><span class="sy1">></span>test_and_set<span class="br0">(</span>order<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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<th>版本四</th>
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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="kw4">bool</span> atomic_flag_test_and_set_explicit<span class="br0">(</span><a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a><span class="sy2">*</span> 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>
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<span class="br0">{</span>
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<span class="kw1">return</span> p<span class="sy2">-</span><span class="sy1">></span>test_and_set<span class="br0">(</span>order<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-example">
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<p>能用 atomic_flag 在用户空间实现自旋锁互斥</p>
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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 <thread></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <atomic></span>
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<a href="cpp-atomic-atomic_flag.html"><span class="kw2088">std::<span class="me2">atomic_flag</span></span></a> lock <span class="sy1">=</span> <a href="cpp-atomic-ATOMIC_FLAG_INIT.html"><span class="kw2091">ATOMIC_FLAG_INIT</span></a><span class="sy4">;</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">int</span> n<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><span class="kw4">int</span> cnt <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> cnt <span class="sy1"><</span> <span class="nu0">100</span><span class="sy4">;</span> <span class="sy2">++</span>cnt<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">while</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">atomic_flag_test_and_set_explicit</span><span class="br0">(</span><span class="sy3">&</span>lock, <a href="cpp-atomic-memory_order.html"><span class="kw2095">std::<span class="me2">memory_order_acquire</span></span></a><span class="br0">)</span><span class="br0">)</span>
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<span class="sy4">;</span> <span class="co1">// 自旋直至获得锁</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">"Output from thread "</span> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">atomic_flag_clear_explicit</span><span class="br0">(</span><span class="sy3">&</span>lock, <a href="cpp-atomic-memory_order.html"><span class="kw2096">std::<span class="me2">memory_order_release</span></span></a><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">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-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="sy1">></span> v<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> <span class="nu0">10</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="br0">{</span>
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v.<span class="me1">emplace_back</span><span class="br0">(</span>f, n<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> t <span class="sy4">:</span> v<span class="br0">)</span> <span class="br0">{</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>
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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">Output from thread 2
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Output from thread 6
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Output from thread 7
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...< 准确 1000 行 >...</pre></div>
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</div>
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</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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<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_flag.html"><span class="t-lines"><span>atomic_flag</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></div>
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</div>
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</td>
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<td>免锁的布尔原子类型<br />
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<span class="t-mark">(类)</span></td>
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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_flag_clear.html"><span class="t-lines"><span>atomic_flag_clear</span><span>atomic_flag_clear_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>原子地设置标志值为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span><br />
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<span class="t-mark">(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-memory_order.html"><span class="t-lines"><span>memory_order</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></div>
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</div>
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</td>
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<td>为给定的原子操作定义内存顺序约束<br />
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<span class="t-mark">(枚举)</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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</body>
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