上传cppreference
This commit is contained in:
@@ -0,0 +1,204 @@
|
||||
<!DOCTYPE html>
|
||||
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
||||
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
||||
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||||
<title>std::condition_variable::wait_until</title>
|
||||
<link rel="stylesheet" href="ext.css" />
|
||||
<link rel="stylesheet" href="site_modules.css" />
|
||||
</head>
|
||||
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_condition_variable_wait_until skin-cppreference2 action-view cpp-page-template cpp-navbar">
|
||||
<div id="cpp-content-base">
|
||||
<div id="content"><a id="top"></a>
|
||||
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::condition_variable::</span>wait_until</h1>
|
||||
<div id="bodyContent">
|
||||
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-thread.html">thread</a>‎ | <a href="cpp-thread-condition_variable.html">condition variable</a></span></div>
|
||||
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
||||
<div class="t-page-template" style="">
|
||||
<p></p>
|
||||
</div>
|
||||
<table class="t-dcl-begin">
|
||||
<tbody>
|
||||
<tr class="t-dcl t-since-cxx11">
|
||||
<td>
|
||||
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Clock, <span class="kw1">class</span> Duration <span class="sy1">></span><br /></span>
|
||||
<p><a href="cpp-thread-cv_status.html"><span class="kw2176">std::<span class="me2">cv_status</span></span></a><br />
|
||||
wait_until<span class="br0">(</span> <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><span class="sy3">&</span> lock,<br /></p>
|
||||
<span class="kw4">const</span> <a href="cpp-chrono-time_point.html"><span class="kw991">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">time_point</span></span></a><span class="sy1"><</span>Clock, Duration<span class="sy1">></span><span class="sy3">&</span> timeout_time <span class="br0">)</span><span class="sy4">;</span></div>
|
||||
</td>
|
||||
<td>(1)</td>
|
||||
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
|
||||
</tr>
|
||||
<tr class="t-dcl t-since-cxx11">
|
||||
<td>
|
||||
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Clock, <span class="kw1">class</span> Duration, <span class="kw1">class</span> Pred <span class="sy1">></span><br /></span>
|
||||
<p><span class="kw4">bool</span> wait_until<span class="br0">(</span> <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><span class="sy3">&</span> lock,<br />
|
||||
<span class="kw4">const</span> <a href="cpp-chrono-time_point.html"><span class="kw991">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">time_point</span></span></a><span class="sy1"><</span>Clock, Duration<span class="sy1">></span><span class="sy3">&</span> timeout_time,<br /></p>
|
||||
Pred pred <span class="br0">)</span><span class="sy4">;</span></div>
|
||||
</td>
|
||||
<td>(2)</td>
|
||||
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
|
||||
</tr>
|
||||
<tr class="t-dcl-sep">
|
||||
<td></td>
|
||||
<td></td>
|
||||
<td></td>
|
||||
</tr>
|
||||
</tbody>
|
||||
</table>
|
||||
<p><code>wait_until</code> 导致当前线程阻塞直至通知条件变量、抵达指定时间或虚假唤醒发生，可选的循环直至满足某谓词。</p>
|
||||
<div class="t-li1"><span class="t-li">1)</span> 原子地释放 <code>lock</code> ，阻塞当前线程，并将它添加到等待在 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 上的线程列表。将在执行 <span class="t-lc"><a href="cpp-thread-condition_variable-notify_all.html">notify_all()</a></span> 或 <span class="t-lc"><a href="cpp-thread-condition_variable-notify_one.html">notify_one()</a></span> 时，或抵达绝对时间点 <code>timeout_time</code> 时解除阻塞线程。亦可能虚假地解除阻塞。解除阻塞时，无关缘由，重获得 <code>lock</code> 并退出 <code>wait_for()</code> 。</div>
|
||||
<div class="t-li1"><span class="t-li">2)</span> 等价于</div>
|
||||
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
||||
<div class="cpp source-cpp">
|
||||
<pre class="de1"><span class="kw1">while</span> <span class="br0">(</span><span class="sy3">!</span>pred<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
|
||||
<span class="kw1">if</span> <span class="br0">(</span>wait_until<span class="br0">(</span>lock, timeout_time<span class="br0">)</span> <span class="sy1">==</span> <a href="cpp-thread-cv_status.html"><span class="kw2178">std::<span class="me2">cv_status</span><span class="sy4">::</span><span class="me2">timeout</span></span></a><span class="br0">)</span> <span class="br0">{</span>
|
||||
<span class="kw1">return</span> pred<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
<span class="br0">}</span>
|
||||
<span class="kw1">return</span> <span class="kw2">true</span><span class="sy4">;</span></pre></div>
|
||||
</div>
|
||||
<div class="t-li1"><span class="t-li"></span> 此重载可用于忽略虚假唤醒。</div>
|
||||
<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>
|
||||
<p>若 <code>lock.mutex()</code> 与所有其他当前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>
|
||||
<p><br />
|
||||
若这些函数不能满足后条件（ <span class="t-c"><span class="mw-geshi cpp source-cpp">lock.<span class="me1">owns_lock</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">==</span><span class="kw2">true</span></span></span> 且调用方线程锁定 <span class="t-c"><span class="mw-geshi cpp source-cpp">lock.<span class="me1">mutex</span><span class="br0">(</span><span class="br0">)</span></span></span> ），则调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span> 。例如，这可能在重锁定互斥抛异常的情况下发生。</p>
|
||||
<p><code>Clock</code> 必须符合<a href="cpp-named_req-Clock.html"><span style="font-style:italic">时钟</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Clock)</span></a> 要求。<span class="t-rev-inl t-since-cxx20"><span>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">is_clock_v</span><span class="sy1"><</span>Clock<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则程序为非良构。</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span></p>
|
||||
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
||||
<table class="t-par-begin">
|
||||
<tr class="t-par">
|
||||
<td>lock</td>
|
||||
<td>-</td>
|
||||
<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><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></span></span> 类型对象，必须被当前线程锁定</td>
|
||||
</tr>
|
||||
<tr class="t-par">
|
||||
<td>timeout_time</td>
|
||||
<td>-</td>
|
||||
<td>表示停止等待时间的 <span class="t-lc"><a href="cpp-chrono-time_point.html">std::chrono::time_point</a></span> 类型对象</td>
|
||||
</tr>
|
||||
<tr class="t-par">
|
||||
<td>pred</td>
|
||||
<td>-</td>
|
||||
<td>是否应该持续等待则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 的谓词。<br />
|
||||
<p>谓词函数的签名应等价于如下者：</p>
|
||||
<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">bool</span> pred<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></span>​</p>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
||||
<div class="t-li1"><span class="t-li">1)</span> 若抵达 <code>timeout_time</code> 指定的的绝对时间点则为 <span class="t-lc"><a href="cpp-thread-cv_status.html">std::cv_status::timeout</a></span> ，否则为 <span class="t-lc"><a href="cpp-thread-cv_status.html">std::cv_status::no_timeout</a></span> 。</div>
|
||||
<div class="t-li1"><span class="t-li">2)</span> 若度过 <code>timeout_time</code> 时限后 <code>pred</code> 仍求值为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。若已度过时限，则求值并返回 <code>pred</code> 的结果。</div>
|
||||
<p><br /></p>
|
||||
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
|
||||
<div class="t-li1"><span class="t-li">1)</span> 执行期间时钟、时间点或时长可能抛出的任何异常（标准库提供的时钟、时间点和时长决不抛出）</div>
|
||||
<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但亦可传播 <code>pred</code> 所抛的异常</div>
|
||||
<p><br /></p>
|
||||
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
||||
<p>使用倾向 <code>timeout_time</code> 的时钟，不要求是单调时钟。若不连续地调节时钟，则不对此函数的行为保证，但既存实现将 <code>timeout_time</code> 从 <code>Clock</code> 转换到 <span class="t-lc"><a href="cpp-chrono-system_clock.html">std::chrono::system_clock</a></span> ，并委托 POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_cond_timedwait.html"><code>pthread_cond_timedwait</code></a> 以令等待忠实于系统时钟，但非用户提供 <code>Clock</code> 的调节。任何情况下，由于调度或资源争议延迟，函数可能等待长于抵达 <code>timeout_time</code> 。</p>
|
||||
<p>即使使用的始终是 <span class="t-lc"><a href="cpp-chrono-steady_clock.html">std::chrono::steady_clock</a></span> 或另一单调时钟，系统时钟调节亦可能导致虚假唤醒。</p>
|
||||
<p><code>notify_one()</code>/<code>notify_all()</code> 的效果与 <code>wait()</code>/<code>wait_for()</code>/<code>wait_until()</code> 的三个原子部分的每一者（解锁+等待、唤醒和锁定）以能看做原子变量<a href="cpp-atomic-memory_order.html#.E4.BF.AE.E6.94.B9.E9.A1.BA.E5.BA.8F">修改顺序</a>单独全序发生：顺序对此单独的 condition_variable 是特定的。譬如，这使得 <code>notify_one()</code> 不可能被延迟并解锁正好在进行 <code>notify_one()</code> 调用后开始等待的线程。</p>
|
||||
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
||||
<div class="t-example">
|
||||
<div class="t-example-live-link"></div>
|
||||
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
||||
<div class="cpp source-cpp">
|
||||
<pre class="de1"><span class="co2">#include <iostream></span>
|
||||
<span class="co2">#include <atomic></span>
|
||||
<span class="co2">#include <condition_variable></span>
|
||||
<span class="co2">#include <thread></span>
|
||||
<span class="co2">#include <chrono></span>
|
||||
<span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">chrono_literals</span><span class="sy4">;</span>
|
||||
|
||||
<a href="cpp-thread-condition_variable.html"><span class="kw2171">std::<span class="me2">condition_variable</span></span></a> cv<span class="sy4">;</span>
|
||||
<a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> cv_m<span class="sy4">;</span>
|
||||
<a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> i<span class="br0">{</span><span class="nu0">0</span><span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw4">void</span> waits<span class="br0">(</span><span class="kw4">int</span> idx<span class="br0">)</span>
|
||||
<span class="br0">{</span>
|
||||
<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>cv_m<span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="kw4">auto</span> now <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">::</span><span class="me2">system_clock</span><span class="sy4">::</span><span class="me2">now</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="kw1">if</span><span class="br0">(</span>cv.<span class="me1">wait_until</span><span class="br0">(</span>lk, now <span class="sy2">+</span> idx<span class="sy2">*</span>100ms, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="br0">)</span><span class="br0">{</span><span class="kw1">return</span> i <span class="sy1">==</span> <span class="nu0">1</span><span class="sy4">;</span><span class="br0">}</span><span class="br0">)</span><span class="br0">)</span>
|
||||
<a href="cpp-io-cerr.html"><span class="kw1760">std::<span class="me2">cerr</span></span></a> <span class="sy1"><<</span> <span class="st0">"Thread "</span> <span class="sy1"><<</span> idx <span class="sy1"><<</span> <span class="st0">" finished waiting. i == "</span> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
||||
<span class="kw1">else</span>
|
||||
<a href="cpp-io-cerr.html"><span class="kw1760">std::<span class="me2">cerr</span></span></a> <span class="sy1"><<</span> <span class="st0">"Thread "</span> <span class="sy1"><<</span> idx <span class="sy1"><<</span> <span class="st0">" timed out. i == "</span> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
|
||||
<span class="kw4">void</span> signals<span class="br0">(</span><span class="br0">)</span>
|
||||
<span class="br0">{</span>
|
||||
<a href="cpp-thread-sleep_for.html"><span class="kw2149">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span>120ms<span class="br0">)</span><span class="sy4">;</span>
|
||||
<a href="cpp-io-cerr.html"><span class="kw1760">std::<span class="me2">cerr</span></span></a> <span class="sy1"><<</span> <span class="st0">"Notifying...<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
||||
cv.<span class="me1">notify_all</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<a href="cpp-thread-sleep_for.html"><span class="kw2149">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span>100ms<span class="br0">)</span><span class="sy4">;</span>
|
||||
i <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
|
||||
<a href="cpp-io-cerr.html"><span class="kw1760">std::<span class="me2">cerr</span></span></a> <span class="sy1"><<</span> <span class="st0">"Notifying again...<span class="es1">\n</span>"</span><span class="sy4">;</span>
|
||||
cv.<span class="me1">notify_all</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
|
||||
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
||||
<span class="br0">{</span>
|
||||
<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span>waits, <span class="nu0">1</span><span class="br0">)</span>, t2<span class="br0">(</span>waits, <span class="nu0">2</span><span class="br0">)</span>, t3<span class="br0">(</span>waits, <span class="nu0">3</span><span class="br0">)</span>, t4<span class="br0">(</span>signals<span class="br0">)</span><span class="sy4">;</span>
|
||||
t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
t2.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
t3.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
t4.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span></pre></div>
|
||||
</div>
|
||||
<p>可能的输出：</p>
|
||||
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
||||
<div class="text source-text">
|
||||
<pre class="de1">Thread 1 timed out. i == 0
|
||||
Notifying...
|
||||
Thread 2 timed out. i == 0
|
||||
Notifying again...
|
||||
Thread 3 finished waiting. i == 1</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
||||
<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>
|
||||
<table class="dsctable" style="font-size:0.8em">
|
||||
<tr>
|
||||
<th>DR</th>
|
||||
<th>应用于</th>
|
||||
<th>出版时的行为</th>
|
||||
<th>正确行为</th>
|
||||
</tr>
|
||||
<tr>
|
||||
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2093">LWG 2093</a></td>
|
||||
<td>C++11</td>
|
||||
<td>规范中缺失超时相关异常</td>
|
||||
<td>已提及</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2135">LWG 2135</a></td>
|
||||
<td>C++11</td>
|
||||
<td><code>wait_until</code> 在解锁/重锁失败时抛异常</td>
|
||||
<td>调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span></td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
||||
<table class="t-dsc-begin">
|
||||
<tr class="t-dsc">
|
||||
<td>
|
||||
<div class="t-dsc-member-div">
|
||||
<div><a href="cpp-thread-condition_variable-wait.html"><span class="t-lines"><span>wait</span></span></a></div>
|
||||
</div>
|
||||
</td>
|
||||
<td>阻塞当前线程，直到条件变量被唤醒<br />
|
||||
<span class="t-mark">(公开成员函数)</span></td>
|
||||
</tr>
|
||||
<tr class="t-dsc">
|
||||
<td>
|
||||
<div class="t-dsc-member-div">
|
||||
<div><a href="cpp-thread-condition_variable-wait_for.html"><span class="t-lines"><span>wait_for</span></span></a></div>
|
||||
</div>
|
||||
</td>
|
||||
<td>阻塞当前线程，直到条件变量被唤醒，或到指定时限时长后<br />
|
||||
<span class="t-mark">(公开成员函数)</span></td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
<div class="visualClear"></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user