222 lines
23 KiB
HTML
222 lines
23 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>std::jthread::jthread</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_thread_jthread_jthread skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::jthread::</span>jthread</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>‎ | <a href="cpp-thread-jthread.html">jthread</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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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp">jthread<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp">jthread<span class="br0">(</span> jthread<span class="sy3">&&</span> other <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<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> Function, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<span class="kw1">explicit</span> jthread<span class="br0">(</span> Function<span class="sy3">&&</span> f, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp">jthread<span class="br0">(</span> <span class="kw4">const</span> jthread<span class="sy3">&</span> <span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>构造新 <code>jthread</code> 对象。</p>
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<div class="t-li1"><span class="t-li">1)</span> 构造不表示线程的新 <code>jthread</code> 对象。</div>
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<div class="t-li1"><span class="t-li">2)</span> 移动构造函数。构造的 <code>jthread</code> 对象表示之前由 <code>other</code> 表示的执行线程。此调用后 <code>other</code> 不再表示执行线程。</div>
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<div class="t-li1"><span class="t-li">3)</span> 创建与执行线程关联的新 <code>jthread</code> 对象。若函数 <i>f</i> 接受 <code>std::stop_token</code> 作为其首参数，则新执行线程开始执行
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f_copy<span class="br0">)</span>, get_stop_token<span class="br0">(</span><span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>args_copy<span class="br0">)</span>...<span class="br0">)</span></span></span> ，若该表达式合法；否则它开始执行</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f_copy<span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>args_copy<span class="br0">)</span>...<span class="br0">)</span></span></span> 。</li>
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</ul>
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<p>任一情况下，</p>
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<ul>
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<li><code>f_copy</code> 为从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Function<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span></span></span> 构造的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>Function<span class="sy1">></span></span></span> 类型对象，而</li>
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<li><code>args_copy...</code> 为从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...</span></span> 构造的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span>...</span></span> 类型对象。</li>
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</ul>
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在调用方的环境执行这些对象的构造，故而在求值和移动/构造参数期间抛出的任何异常都在当前线程抛出，而不会开始新线程。若任何构造或 <span class="t-lc"><a href="cpp-utility-functional-invoke.html">std::invoke</a></span> 调用非法则程序非良构。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>Function<span class="sy1">></span></span></span> 与 <code>jthread</code> 为相同类型则此构造函数不参与重载决议。</div>
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<div class="t-li1"><span class="t-li"></span> 构造函数的完成<i>同步于</i>（按 <span class="t-lc"><a href="cpp-atomic-memory_order.html">std::memory_order</a></span> 中定义） <i>f</i> 的副本在新线程上调用的开始。</div>
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<div class="t-li1"><span class="t-li">4)</span> 复制构造函数被删除；线程不可复制。没有二个 <code>std::jthread</code> 对象可表示同一执行线程。</div>
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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>other</td>
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<td>-</td>
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<td>用以构造此 <code>jthread</code> 对象的另一 <code>jthread</code> 对象</td>
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</tr>
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<tr class="t-par">
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<td>f</td>
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<td>-</td>
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<td>执行于新线程的<a href="cpp-named_req-Callable.html"><span style="font-style:italic">可调用</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Callable)</span></a> 对象</td>
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</tr>
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<tr class="t-par">
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<td>args...</td>
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<td>-</td>
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<td>传递给函数的参数</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.90.8E.E6.9D.A1.E4.BB.B6">后条件</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> <span class="t-lc">get_id()</span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">jthread</span><span class="sy4">::</span><span class="me2">id</span><span class="br0">(</span><span class="br0">)</span></span></span> （即 <span class="t-lc">joinable()</span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ）而 <span class="t-lc">get_stop_source().stop_possible()</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</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">other.<span class="me1">get_id</span><span class="br0">(</span><span class="br0">)</span></span></span> 等于 <span class="t-lc">std::jthread::id()</span> 而 <span class="t-lc">get_id()</span> 返回构造开始前 <span class="t-c"><span class="mw-geshi cpp source-cpp">other.<span class="me1">get_id</span><span class="br0">(</span><span class="br0">)</span></span></span> 的值</div>
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<div class="t-li1"><span class="t-li">3)</span> <span class="t-lc">get_id()</span> 不等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">jthread</span><span class="sy4">::</span><span class="me2">id</span><span class="br0">(</span><span class="br0">)</span></span></span> （即 <span class="t-lc">joinable()</span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ），而 <span class="t-lc">get_stop_source().stop_possible()</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">3)</span> 若不能开始线程则为 <span class="t-lc"><a href="cpp-error-system_error.html">std::system_error</a></span> 。异常可表示错误条件 <code>std::errc::resource_unavailable_try_again</code> 或另一实现特定的错误条件。</div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>按值复制或移动给线程函数的参数。若需要传递给线程函数引用参数，则必须包装它（例如用 <span class="t-lc"><a href="cpp-utility-functional-ref.html">std::ref</a></span> 或 <span class="t-lc"><a href="cpp-utility-functional-ref.html">std::cref</a></span> ）。</p>
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<p>忽略来自函数的任何返回值。若函数抛异常，则调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span> 。为将返回值或异常传回调用线程，可使用 <span class="t-lc"><a href="cpp-thread-promise.html">std::promise</a></span> 或 <span class="t-lc"><a href="cpp-thread-async.html">std::async</a></span> 。</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 <utility></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="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">literals</span><span class="sy4">;</span>
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<span class="kw4">void</span> f1<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> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="sy2">++</span>i<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">"Thread 1 executing<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="sy2">++</span>n<span class="sy4">;</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>10ms<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> f2<span class="br0">(</span><span class="kw4">int</span><span class="sy3">&</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> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="sy2">++</span>i<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">"Thread 2 executing<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="sy2">++</span>n<span class="sy4">;</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>10ms<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="kw1">class</span> foo
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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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<span class="kw4">void</span> bar<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><span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="sy2">++</span>i<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">"Thread 3 executing<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="sy2">++</span>n<span class="sy4">;</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>10ms<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> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">class</span> baz
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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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<span class="kw4">void</span> operator<span class="br0">(</span><span class="br0">)</span><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><span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="sy2">++</span>i<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">"Thread 4 executing<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="sy2">++</span>n<span class="sy4">;</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>10ms<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> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</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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<span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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foo f<span class="sy4">;</span>
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baz b<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t0<span class="sy4">;</span> <span class="co1">// t0 不是线程</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t1<span class="br0">(</span>f1, n <span class="sy2">+</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 按值传递</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t2a<span class="br0">(</span>f2, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>n<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 按引用传递</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t2b<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>t2a<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// t2b 现在运行 f2() 。 t2a 不再是线程</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t3<span class="br0">(</span><span class="sy3">&</span>foo<span class="sy4">::</span><span class="me2">bar</span>, <span class="sy3">&</span>f<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// t3 在对象 f 上运行 foo::bar()</span>
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std<span class="sy4">::</span><span class="me2">jthread</span> t4<span class="br0">(</span>b<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// t4 在对象 b 的副本上运行 baz::operator()</span>
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t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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t2b.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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t3.<span class="me1">join</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> <span class="st0">"Final value of n is "</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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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Final value of f.n (foo::n) is "</span> <span class="sy1"><<</span> f.<span class="me1">n</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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">"Final value of b.n (baz::n) is "</span> <span class="sy1"><<</span> b.<span class="me1">n</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// t4 在析构时结合</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">Thread 2 executing
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Thread 1 executing
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Thread 4 executing
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Thread 3 executing
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Thread 3 executing
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Thread 4 executing
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Thread 2 executing
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Thread 1 executing
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Thread 3 executing
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Thread 1 executing
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Thread 4 executing
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Thread 2 executing
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Thread 3 executing
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Thread 1 executing
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Thread 4 executing
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Thread 2 executing
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Thread 3 executing
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Thread 1 executing
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Thread 4 executing
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Thread 2 executing
|
|
Final value of n is 5
|
|
Final value of f.n (foo::n) is 5
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Final value of b.n (bar::n) is 0</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 t-dsc-member-nobold-div">
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<div><a href="cpp-thread-thread-thread.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
|
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</div>
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</td>
|
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<td>构造新的 thread 对象<br />
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<span class="t-mark">(<code>std::thread</code> 的公开成员函数)</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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</div>
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</body>
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</html>
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