227 lines
15 KiB
HTML
227 lines
15 KiB
HTML
<!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::future</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_future skin-cppreference2 action-view 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::</span>future</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-thread.html">thread</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><a href="cpp-header-future.html"><future></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></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> T <span class="sy1">></span> <span class="kw1">class</span> future<span class="sy4">;</span></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> T <span class="sy1">></span> <span class="kw1">class</span> future<span class="sy1"><</span>T<span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span></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 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> future<span class="sy1"><</span><span class="kw4">void</span><span class="sy1">></span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(3)</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>类模板 <code>std::future</code> 提供访问异步操作结果的机制:</p>
|
|
<ul>
|
|
<li>(通过 <span class="t-lc"><a href="cpp-thread-async.html">std::async</a></span> 、 <span class="t-lc"><a href="cpp-thread-packaged_task.html">std::packaged_task</a></span> 或 <span class="t-lc"><a href="cpp-thread-promise.html">std::promise</a></span> 创建的)异步操作能提供一个 <code>std::future</code> 对象给该异步操作的创建者。</li>
|
|
</ul>
|
|
<ul>
|
|
<li>然后,异步操作的创建者能用各种方法查询、等待或从 <code>std::future</code> 提取值。若异步操作仍未提供值,则这些方法可能阻塞。</li>
|
|
</ul>
|
|
<ul>
|
|
<li>异步操作准备好发送结果给创建者时,它能通过修改链接到创建者的 <code>std::future</code> 的<i>共享状态</i>(例如 <span class="t-lc"><a href="cpp-thread-promise-set_value.html">std::promise::set_value</a></span> )进行。</li>
|
|
</ul>
|
|
<p>注意, <code>std::future</code> 所引用的共享状态不与另一异步返回对象共享(与 <span class="t-lc"><a href="cpp-thread-shared_future.html">std::shared_future</a></span> 相反)。</p>
|
|
<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div t-dsc-member-nobold-div">
|
|
<div><a href="cpp-thread-future-future.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>构造 future 对象<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 t-dsc-member-nobold-div">
|
|
<div><a href="cpp-thread-future-~future.html"><span class="t-lines"><span>(析构函数)</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>析构 future 对象<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-future-operator=.html"><span class="t-lines"><span>operator=</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>移动future对象<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-future-share.html"><span class="t-lines"><span>share</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>从 <code>*this</code> 转移共享状态给 <a href="cpp-thread-shared_future.html"><tt>shared_future</tt></a> 并返回它<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E8.8E.B7.E5.8F.96.E7.BB.93.E6.9E.9C">获取结果</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-thread-future-get.html"><span class="t-lines"><span>get</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回结果<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E7.8A.B6.E6.80.81">状态</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-thread-future-valid.html"><span class="t-lines"><span>valid</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查 future 是否拥有共享状态<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-future-wait.html"><span class="t-lines"><span>wait</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>等待结果变得可用<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-future-wait_for.html"><span class="t-lines"><span>wait_for</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>等待结果,如果在指定的超时间隔后仍然无法得到结果,则返回。<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-future-wait_until.html"><span class="t-lines"><span>wait_until</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<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 />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
<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 <future></span>
|
|
<span class="co2">#include <thread></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="co1">// 来自 packaged_task 的 future</span>
|
|
<a href="cpp-thread-packaged_task.html"><span class="kw2182">std::<span class="me2">packaged_task</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span> task<span class="br0">(</span><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> <span class="nu0">7</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 包装函数</span>
|
|
std<span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> f1 <span class="sy1">=</span> task.<span class="me1">get_future</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 获取 future</span>
|
|
<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>task<span class="br0">)</span><span class="br0">)</span>.<span class="me1">detach</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 在线程上运行</span>
|
|
|
|
<span class="co1">// 来自 async() 的 future</span>
|
|
std<span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> f2 <span class="sy1">=</span> <a href="cpp-thread-async.html"><span class="kw2183">std::<span class="me2">async</span></span></a><span class="br0">(</span><a href="cpp-thread-launch.html"><span class="kw2185">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> <span class="kw1">return</span> <span class="nu0">8</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 来自 promise 的 future</span>
|
|
<a href="cpp-thread-promise.html"><span class="kw2179">std::<span class="me2">promise</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> p<span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> f3 <span class="sy1">=</span> p.<span class="me1">get_future</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="br0">(</span> <span class="br0">[</span><span class="sy3">&</span>p<span class="br0">]</span><span class="br0">{</span> p.<span class="me1">set_value_at_thread_exit</span><span class="br0">(</span><span class="nu0">9</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span>.<span class="me1">detach</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<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> <span class="sy1"><<</span> <a href="cpp-io-manip-flush.html"><span class="kw1790">std::<span class="me2">flush</span></span></a><span class="sy4">;</span>
|
|
f1.<span class="me1">wait</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
f2.<span class="me1">wait</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
f3.<span class="me1">wait</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Done!<span class="es1">\n</span>Results are: "</span>
|
|
<span class="sy1"><<</span> f1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> f2.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> f3.<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>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出:</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">Waiting...Done!
|
|
Results are: 7 8 9</pre></div>
|
|
</div>
|
|
</div>
|
|
<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-async.html"><span class="t-lines"><span>async</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>异步运行一个函数(有可能在新线程中执行),并返回保有其结果的 <span class="t-lc"><strong class="selflink">std::future</strong></span><br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-thread-shared_future.html"><span class="t-lines"><span>shared_future</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>等待被异步设置的值(可能为其他 future 所引用)<br />
|
|
<span class="t-mark">(类模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|