141 lines
11 KiB
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141 lines
11 KiB
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<title>std::notify_all_at_thread_exit</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_notify_all_at_thread_exit 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>notify_all_at_thread_exit</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></span></div>
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<table class="t-dcl-begin">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-condition_variable.html"><condition_variable></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> notify_all_at_thread_exit<span class="br0">(</span> <a href="cpp-thread-condition_variable.html"><span class="kw2171">std::<span class="me2">condition_variable</span></span></a><span class="sy3">&</span> cond,<br />
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<a href="cpp-thread-unique_lock.html"><span class="kw2167">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p><code>notify_all_at_thread_exit</code> 提供机制，通知其他线程给定的线程已完全完成，包括销毁所有 <a href="cpp-keyword-thread_local.html">thread_local</a> 对象。它操作如下：</p>
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<ul>
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<li>将先前获得的锁 <code>lk</code> 的所有权转移到内部存储。</li>
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</ul>
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<ul>
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<li>修改执行环境，以令当前线程退出时，如同以下列方式通知 condition_variable <code>cond</code> ：</li>
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</ul>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">lk.<span class="me1">unlock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span><br />
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cond.<span class="me1">notify_all</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>隐含的 <code>lk.unlock</code> <i>后序于</i>（定义于 <span class="t-lc"><a href="cpp-atomic-memory_order.html">std::memory_order</a></span> ）关联到当前线程的，所有拥有<a href="cpp-keyword-thread_local.html">线程局域存储期</a>的对象析构。</p>
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<p>等价的效果可以用 <span class="t-lc"><a href="cpp-thread-promise.html">std::promise</a></span> 或 <span class="t-lc"><a href="cpp-thread-packaged_task.html">std::packaged_task</a></span> 所提供的设施达成。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>若当前线程未锁定 <code>lock.mutex()</code> ，则调用此函数是未定义行为。</p>
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<p>若 <code>lock.mutex()</code> 与所有其他等待在同一条件变量上的线程所用的互斥不相同，则调用此函数是未定义行为。</p>
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<p>保有提供的锁 <code>lk</code> 直至线程退出。一旦调用此函数，则无更多线程可获得相同的锁，以在 <code>cond</code> 上等待。若某线程在此条件变量上等待，则它在虚假唤醒时不应试图释放和重获得锁。</p>
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<p>典型使用情况中，此函数是被脱附线程所做的最后行动。</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>cond</td>
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<td>-</td>
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<td>在线程退出时通知的 conditional_variable</td>
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</tr>
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<tr class="t-par">
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<td>lk</td>
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<td>-</td>
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<td>关联到 condition_variable <code>cond</code> 的锁</td>
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</tr>
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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=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>此部分代码零碎地描绘 <code>notify_all_at_thread_exit</code> 能如何用于避免在线程局域对象处于被析构过程时，访问依赖于它们的数据：</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 <mutex></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <condition_variable></span>
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<a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> m<span class="sy4">;</span>
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<a href="cpp-thread-condition_variable.html"><span class="kw2171">std::<span class="me2">condition_variable</span></span></a> cv<span class="sy4">;</span>
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<span class="kw4">bool</span> ready <span class="sy1">=</span> <span class="kw2">false</span><span class="sy4">;</span>
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ComplexType result<span class="sy4">;</span> <span class="co1">// 一些任意类型</span>
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<span class="kw4">void</span> thread_func<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-thread-unique_lock.html"><span class="kw2167">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 用 thread_local 数据赋值给 result</span>
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result <span class="sy1">=</span> function_that_uses_thread_locals<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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ready <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">notify_all_at_thread_exit</span><span class="br0">(</span>cv, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>lk<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="co1">// 1. 销毁 thread_local 对象， 2. 解锁互斥， 3. 通知 cv</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-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> t<span class="br0">(</span>thread_func<span class="br0">)</span><span class="sy4">;</span>
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t.<span class="me1">detach</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 做其他工作</span>
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<span class="co1">// .…</span>
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<span class="co1">// 等待脱附的线程</span>
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<a href="cpp-thread-unique_lock.html"><span class="kw2167">std::<span class="me2">unique_lock</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>m<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">while</span><span class="br0">(</span><span class="sy3">!</span>ready<span class="br0">)</span> <span class="br0">{</span>
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cv.<span class="me1">wait</span><span class="br0">(</span>lk<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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process<span class="br0">(</span>result<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// result 已准备且 thread_local 析构函数已完成</span>
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<span class="br0">}</span></pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-promise-set_value_at_thread_exit.html"><span class="t-lines"><span>set_value_at_thread_exit</span></span></a></div>
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</div>
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</td>
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<td>设置结果为指定值，同时仅在线程退出时分发提醒<br />
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<span class="t-mark">(<code>std::promise<R></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-thread-packaged_task-make_ready_at_thread_exit.html"><span class="t-lines"><span>make_ready_at_thread_exit</span></span></a></div>
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</div>
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</td>
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<td>执行函数，并确保结果仅在一旦当前线程退出时就绪<br />
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<span class="t-mark">(<code>std::packaged_task<R(Args...)></code> 的公开成员函数)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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