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79 lines
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<title>std::experimental::when_any</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::</span>when_any</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a></span></div>
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<div>定义于头文件 <code><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/header/experimental/future&action=edit&redlink=1" class="new" title="cpp/header/experimental/future（页面不存在）"><experimental/future></a></code></div>
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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> Sequence <span class="sy1">></span><br /></span>
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<p><span class="kw1">struct</span> when_any_result <span class="br0">{</span><br />
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> index<span class="sy4">;</span><br />
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Sequence futures<span class="sy4">;</span><br /></p>
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<span class="br0">}</span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-concurrency-ts t-mark-ts">(并发 TS)</span></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> InputIt <span class="sy1">></span><br /></span>
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<p><span class="kw4">auto</span> when_any<span class="br0">(</span>InputIt first, InputIt last<span class="br0">)</span><span class="sy4">;</span><br />
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<span class="sy2">-</span><span class="sy1">></span> future<span class="sy1"><</span>when_any_result<span class="sy1"><</span><br />
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>InputIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span><span class="sy1">></span><br /></p>
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<span class="sy1">>></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-concurrency-ts t-mark-ts">(并发 TS)</span></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>... <span class="me1">Futures</span> <span class="sy1">></span><br /></span>
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<p><span class="kw4">auto</span> when_any<span class="br0">(</span>Futures<span class="sy3">&&</span>... <span class="me1">futures</span><span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> future<span class="sy1"><</span>when_any_result<span class="sy1"><</span><a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>Futures<span class="sy1">></span>...<span class="sy1">>>></span><span class="sy4">;</span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-concurrency-ts t-mark-ts">(并发 TS)</span></td>
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<p>创建 <span class="t-lc">future</span> 对象，它在至少一个输入 <code>future</code> 和 <span class="t-lc">shared_future</span> 就绪时变为就绪。若任何输入 <code>future</code> 或 <code>shared_future</code> 非法则行为未定义。</p>
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<p>具体而言，令 <code>Sequence</code> 对 <span class="t-v">(1)</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>InputIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span><span class="sy1">></span></span></span> ，对 <span class="t-v">(2)</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>Futures<span class="sy1">></span>...<span class="sy1">></span></span></span> 。此函数模板创建含 <code>when_any_result<Sequence></code> 的共享状态，并返回指代该共享状态的 <code>future</code> 。移动每个输入 <code>future</code> 到共享状态中的 <code>when_any_result<Sequence></code> 的 <code>futures</code> 成员的对应对象中，复制每个输入 <code>shared_future</code> 到共享状态中的 <code>when_any_result<Sequence></code> 的 <code>futures</code> 成员中的对应对象。 <code>Sequence</code> 中的对象顺序匹配参数的顺序。</p>
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<div class="t-li1"><span class="t-li">1)</span> 此函数仅若 <code>InputIt</code> 的值类型（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>InputIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span></span></span> ）为 <span class="t-lc">std::experimental::future</span> 或 <span class="t-lc">std::experimental::shared_future</span> 才参与重载决议。</div>
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<div class="t-li1"><span class="t-li">2)</span> 此函数仅若每个参数为（可有 cv 限定的） <span class="t-lc">std::experimental::shared_future</span> 或无 cv 限定的 <span class="t-lc">std::experimental::future</span> 才参与重载决议（正式而言，对于 <code>Futures</code> 中的每个 <code>Fn</code> ，要么 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1"><</span>Fn<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">future</span><span class="sy1"><</span>Rn<span class="sy1">></span></span></span> ，要么 <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>Fn<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">shared_future</span><span class="sy1"><</span>Rn<span class="sy1">></span></span></span> ）。</div>
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<p>此调用后，每个输入 <code>future</code> 不再合法；每个输入 <code>shared_future</code> 保持合法。</p>
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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>指代此调用所创建的共享状态的 <code>future</code> 。该 <code>future</code> 始终为 <span class="t-c"><span class="mw-geshi cpp source-cpp">valid<span class="br0">(</span><span class="br0">)</span></span></span> ，而它在至少一个调用的输入 <code>future</code> 和 <code>shared_future</code> 就绪时变为就绪。 <code>when_any_result</code> 的 <code>index</code> 成员含有 <span class="t-c"><span class="mw-geshi cpp source-cpp">futures</span></span> 成员中就绪的 <code>future</code> 或 <code>shared_future</code> 的位置。</p>
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<div class="t-li1"><span class="t-li">1)</span> 若范围为空（即 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy1">==</span> last</span></span> ），则返回的 <code>future</code> 立即就绪； <code>when_any_result</code> 的 <code>futures</code> 域为空 <code>vector</code> ，而 <code>index</code> 域为 <span class="t-c"><span class="mw-geshi cpp source-cpp">size_t<span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 若不提供参数，则返回的 <code>future</code> 立即就绪； <code>when_any_result</code> 的 <code>futures</code> 域为空 <code>tuple</code> ，而 <code>index</code> 域为 <span class="t-c"><span class="mw-geshi cpp source-cpp">size_t<span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。</div>
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