130 lines
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130 lines
14 KiB
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<title>std::experimental::packaged_task<R(Args...)>::packaged_task (库基础 TS)</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::packaged_task<R(Args...)>::</span>packaged_task <span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 TS)</span></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a>‎ | <a href="cpp-experimental-lib_extensions.html">lib extensions</a>‎ | <a href="cpp-experimental-lib_extensions-packaged_task.html">packaged task</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">packaged_task<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 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> F<span class="sy1">></span><br />
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<span class="kw1">explicit</span> packaged_task<span class="br0">(</span> F<span class="sy3">&&</span> f <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 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> F, <span class="kw1">class</span> Allocator<span class="sy1">></span><br />
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<span class="kw1">explicit</span> packaged_task<span class="br0">(</span> <a href="cpp-memory-allocator_arg_t.html"><span class="kw702">std::<span class="me2">allocator_arg_t</span></span></a>, <span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc, F<span class="sy3">&&</span> f <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 TS)</span></td>
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<div><span class="mw-geshi cpp source-cpp">packaged_task<span class="br0">(</span> <span class="kw4">const</span> packaged_task<span class="sy3">&</span> <span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 TS)</span></td>
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<div><span class="mw-geshi cpp source-cpp">packaged_task<span class="br0">(</span> packaged_task<span class="sy3">&&</span> rhs <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(库基础 TS)</span></td>
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<p>构造新的 <code>std::experimental::packaged_task</code> 对象。</p>
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<div class="t-li1"><span class="t-li">1)</span> 构造无任务且无共享状态的 <code>std::experimental::packaged_task</code> 对象。</div>
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<div class="t-li1"><span class="t-li">2)</span> 构造拥有共享状态和任务副本的 <code>std::experimental::packaged_task</code> 对象，以 <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>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span></span></span> 初始化。此构造函数仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-thread-packaged_task.html"><span class="kw2183">std::<span class="me2">packaged_task</span></span></a><span class="sy1"><</span>R<span class="br0">(</span>ArgTypes...<span class="br0">)</span><span class="sy1">></span></span></span> 为同一类型才参与重载决议。</div>
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<div class="t-li1"><span class="t-li">3)</span> 构造拥有共享状态和任务副本的 <code>std::experimental::packaged_task</code> 对象，以 <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>F<span class="sy1">></span><span class="br0">(</span>f<span class="br0">)</span></span></span> 初始化。用提供的分配器分配存储任务所需的内存，分配器被当做类型擦除的分配器（见后述）。此构造函数仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>F<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-thread-packaged_task.html"><span class="kw2183">std::<span class="me2">packaged_task</span></span></a><span class="sy1"><</span>R<span class="br0">(</span>ArgTypes...<span class="br0">)</span><span class="sy1">></span></span></span> 为相同类型才参与重载决议。</div>
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<div class="t-li1"><span class="t-li">4)</span> 复制构造函数被删除， <code>std::experimental::packaged_task</code> 为仅移动。</div>
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<div class="t-li1"><span class="t-li">5)</span> 构造拥有共享对象和 <code>rhs</code> 先前占有的任务的 <code>std::experimental::packaged_task</code> ，并使 <code>rhs</code> 有无共享状态和被移动的任务。</div>
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<h3><span class="mw-headline" id=".E7.B1.BB.E5.9E.8B.E6.93.A6.E9.99.A4.E7.9A.84.E5.88.86.E9.85.8D.E5.99.A8">类型擦除的分配器</span></h3>
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<p><code>packaged_task</code> 的接收分配器参数 <code>alloc</code> 的构造函数将参数当做类型擦除的分配器。以分配器参数（若指定）确定 <code>packaged_task</code> 用来分配内存的 memory_resource 指针，如下：</p>
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<td><code>alloc</code> 的类型</td>
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<td>memory_resource 指针的值</td>
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<tr class="t-dsc">
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<td>不存在（构造时不指定分配器）</td>
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<td>构造时 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="http://zh.cppreference.com/w/cpp/experimental/get_default_resource"><span class="kw2312">std::<span class="me2">experimental</span><span class="sy4">::</span><span class="me2">pmr</span><span class="sy4">::</span><span class="me2">get_default_resource</span></span></a><span class="br0">(</span><span class="br0">)</span></span></span> 的值。</td>
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<td><span class="t-lc"><a href="cpp-types-nullptr_t.html">std::nullptr_t</a></span></td>
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<td>构造时 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="http://zh.cppreference.com/w/cpp/experimental/get_default_resource"><span class="kw2312">std::<span class="me2">experimental</span><span class="sy4">::</span><span class="me2">pmr</span><span class="sy4">::</span><span class="me2">get_default_resource</span></span></a><span class="br0">(</span><span class="br0">)</span></span></span> 的值。</td>
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<td>可转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="http://zh.cppreference.com/w/cpp/experimental/memory_resource"><span class="kw2304">std::<span class="me2">experimental</span><span class="sy4">::</span><span class="me2">pmr</span><span class="sy4">::</span><span class="me2">memory_resource</span></span></a><span class="sy2">*</span></span></span><br />
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的指针类型</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><a href="http://zh.cppreference.com/w/cpp/experimental/memory_resource"><span class="kw2304">std::<span class="me2">experimental</span><span class="sy4">::</span><span class="me2">pmr</span><span class="sy4">::</span><span class="me2">memory_resource</span></span></a><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>alloc<span class="br0">)</span></span></span></td>
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<td><span class="t-lc"><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/polymorphic_allocator&action=edit&redlink=1" class="new" title="cpp/experimental/polymorphic allocator（页面不存在）">std::experimental::pmr::polymorphic_allocator</a></span><br />
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的特化</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">alloc.<span class="me1">resource</span><span class="br0">(</span><span class="br0">)</span></span></span></td>
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<td>任何其他符合<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 要求的类型</td>
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<td>指向 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-experimental-resource_adaptor.html"><span class="kw2309">std::<span class="me2">experimental</span><span class="sy4">::</span><span class="me2">pmr</span><span class="sy4">::</span><span class="me2">resource_adaptor</span></span></a><span class="sy1"><</span>A<span class="sy1">></span><span class="br0">(</span>alloc<span class="br0">)</span></span></span> 类型对象的指针，其中 <code>A</code> 是 <code>alloc</code> 的类型。指针仅在 <code>packaged_task</code> 对象的生存期内保持合法。</td>
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<td>非以上类型</td>
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<td>程序为病式</td>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>f</td>
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<td>-</td>
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<td>要执行的可调用目标（函数、成员函数、 lambda 表达式、仿函数）</td>
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<td>alloc</td>
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<td>-</td>
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<td>存储任务时使用的分配器</td>
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<td>rhs</td>
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<td>-</td>
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<td>要移动的 <code>std::experimental::packaged_task</code></td>
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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">2-3)</span> 任何 <code>f</code> 的复制/移动构造函数可能抛出的异常，及可能的 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> ，若分配失败。</div>
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<div class="t-li1"><span class="t-li">4)</span> （无）</div>
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</div>
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<div class="visualClear"></div>
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