142 lines
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142 lines
12 KiB
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<title>std::shared_future<T>::wait_for</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_shared_future_wait_for skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::shared_future<T>::</span>wait_for</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-thread.html">thread</a>‎ | <a href="cpp-thread-shared_future.html">shared future</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div class="t-page-template" style="">
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<p></p>
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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> Rep, <span class="kw1">class</span> Period <span class="sy1">></span><br />
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<a href="cpp-thread-future_status.html"><span class="kw2188">std::<span class="me2">future_status</span></span></a> wait_for<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-chrono-duration.html"><span class="kw993">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">duration</span></span></a><span class="sy1"><</span>Rep,Period<span class="sy1">></span><span class="sy3">&</span> timeout_duration <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>等待结果变得可用。阻塞直至经过指定的 <code>timeout_duration</code> ，或结果变为可用，两者的先到来者。返回值鉴别结果的状态。</p>
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<p>此函数可能由于调度或资源争议延迟而阻塞长于 <code>timeout_duration</code> 。</p>
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<p>推荐标准库用稳定时钟度量时长。若实现用系统时钟代替，则等待时间可能也对时钟调整敏感。</p>
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<p>若调用此函数前 <a href="cpp-thread-future-valid.html"><span class="t-c"><span class="mw-geshi cpp source-cpp">valid<span class="br0">(</span><span class="br0">)</span></span></span></a><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">==</span> <span class="kw2">false</span></span></span> 则行为未定义。</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>timeout_duration</td>
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<td>-</td>
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<td>要阻塞的最大时长</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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<td>常量</td>
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<td>解释</td>
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<tr class="t-dsc">
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<td><a href="cpp-thread-future_status.html"><tt>future_status::deferred</tt></a></td>
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<td>共享状态持有的函数正在延迟运行，结果将仅在显式请求时计算</td>
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<tr class="t-dsc">
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<td><a href="cpp-thread-future_status.html"><tt>future_status::ready</tt></a></td>
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<td>共享状态就绪</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-thread-future_status.html"><tt>future_status::timeout</tt></a></td>
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<td>共享状态在经过指定的等待时间内仍未就绪</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>时钟、时间点或时长在执行中可能抛的任何异常（标准库提供的时钟、时间点和时长决不抛出）。</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>鼓励实现在调用前检测 <span class="t-c"><span class="mw-geshi cpp source-cpp">valid <span class="sy1">==</span> <span class="kw2">false</span></span></span> 的情况并抛出以 <a href="cpp-thread-future_errc.html"><span class="t-c"><span class="mw-geshi cpp source-cpp">future_errc<span class="sy4">::</span><span class="me2">no_state</span></span></span></a> 为 error_condition 的 <a href="cpp-thread-future_error.html"><span class="t-c"><span class="mw-geshi cpp source-cpp">future_error</span></span></a> 。</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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<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 <future></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="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-shared_future.html"><span class="kw2181">std::<span class="me2">shared_future</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> future <span class="sy1">=</span> <a href="cpp-thread-async.html"><span class="kw2184">std::<span class="me2">async</span></span></a><span class="br0">(</span><a href="cpp-thread-launch.html"><span class="kw2186">std::<span class="me2">launch</span><span class="sy4">::</span><span class="me2">async</span></span></a>, <span class="br0">[</span><span class="br0">]</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="kw2149">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="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="nu0">8</span><span class="sy4">;</span>
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<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> <span class="st0">"waiting...<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<a href="cpp-thread-future_status.html"><span class="kw2188">std::<span class="me2">future_status</span></span></a> status<span class="sy4">;</span>
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<span class="kw1">do</span> <span class="br0">{</span>
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status <span class="sy1">=</span> future.<span class="me1">wait_for</span><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>status <span class="sy1">==</span> <a href="cpp-thread-future_status.html"><span class="kw2191">std::<span class="me2">future_status</span><span class="sy4">::</span><span class="me2">deferred</span></span></a><span class="br0">)</span> <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">"deferred<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span>status <span class="sy1">==</span> <a href="cpp-thread-future_status.html"><span class="kw2190">std::<span class="me2">future_status</span><span class="sy4">::</span><span class="me2">timeout</span></span></a><span class="br0">)</span> <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">"timeout<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span>status <span class="sy1">==</span> <a href="cpp-thread-future_status.html"><span class="kw2189">std::<span class="me2">future_status</span><span class="sy4">::</span><span class="me2">ready</span></span></a><span class="br0">)</span> <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">"ready!<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span> <span class="kw1">while</span> <span class="br0">(</span>status <span class="sy3">!</span><span class="sy1">=</span> <a href="cpp-thread-future_status.html"><span class="kw2189">std::<span class="me2">future_status</span><span class="sy4">::</span><span class="me2">ready</span></span></a><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">"result is "</span> <span class="sy1"><<</span> future.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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>可能的输出：</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">waiting...
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timeout
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timeout
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ready!
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result is 8</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-shared_future-wait.html"><span class="t-lines"><span>wait</span></span></a></div>
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</div>
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</td>
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<td>等待结果变得可用<br />
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<span class="t-mark">(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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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-shared_future-wait_until.html"><span class="t-lines"><span>wait_until</span></span></a></div>
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</div>
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</td>
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<td>等待结果，如果在已经到达指定的时间点时仍然无法得到结果，则返回。<br />
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<span class="t-mark">(公开成员函数)</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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</body>
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