161 lines
14 KiB
HTML
161 lines
14 KiB
HTML
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<title>std::shared_lock<Mutex>::shared_lock</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::shared_lock<Mutex>::</span>shared_lock</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_lock.html">shared lock</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">shared_lock<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-cxx14">(C++14 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">shared_lock<span class="br0">(</span> shared_lock<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>(2)</td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m <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-cxx14">(C++14 起)</span></td>
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<tr class="t-dcl t-since-cxx14">
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<div><span class="mw-geshi cpp source-cpp">shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m, <a href="cpp-thread-lock_tag_t.html"><span class="kw2160">std::<span class="me2">defer_lock_t</span></span></a> t <span class="br0">)</span> <span class="kw1">noexcept</span><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-cxx14">(C++14 起)</span></td>
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<tr class="t-dcl t-since-cxx14">
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<div><span class="mw-geshi cpp source-cpp">shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m, <a href="cpp-thread-lock_tag_t.html"><span class="kw2161">std::<span class="me2">try_to_lock_t</span></span></a> t <span class="br0">)</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-cxx14">(C++14 起)</span></td>
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<tr class="t-dcl t-since-cxx14">
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<div><span class="mw-geshi cpp source-cpp">shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m, <a href="cpp-thread-lock_tag_t.html"><span class="kw2162">std::<span class="me2">adopt_lock_t</span></span></a> t <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</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> Rep, <span class="kw1">class</span> Period <span class="sy1">></span><br /></span>
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<p>shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m,<br /></p>
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<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="sy4">;</span></div>
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<td>(7)</td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<tr class="t-dcl t-since-cxx14">
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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> Clock, <span class="kw1">class</span> Duration <span class="sy1">></span><br /></span>
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<p>shared_lock<span class="br0">(</span> mutex_type<span class="sy3">&</span> m,<br /></p>
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<span class="kw4">const</span> <a href="cpp-chrono-time_point.html"><span class="kw991">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">time_point</span></span></a><span class="sy1"><</span>Clock,Duration<span class="sy1">></span><span class="sy3">&</span> timeout_time <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(8)</td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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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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<p>构造 <code>shared_lock</code> ，可选地锁定提供的互斥。</p>
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<div class="t-li1"><span class="t-li">1)</span> 构造 <code>shared_lock</code> ，不关联互斥。</div>
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<div class="t-li1"><span class="t-li">2)</span> 移动构造函数。以 <code>other</code> 的内容初始化 <code>shared_lock</code> 。令 <code>other</code> 不关联到互斥。</div>
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<div class="t-li1"><span class="t-li">3-8)</span> 构造 <code>shared_lock</code> ，以 <code>m</code> 为关联的互斥。另外：</div>
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<div class="t-li2"><span class="t-li">3)</span> 通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">m.<span class="me1">lock_shared</span><span class="br0">(</span><span class="br0">)</span></span></span> ，以共享模式锁定关联的互斥。</div>
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<div class="t-li2"><span class="t-li">4)</span> 不锁定关联的互斥。</div>
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<div class="t-li2"><span class="t-li">5)</span> 尝试通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">m.<span class="me1">try_lock_shared</span><span class="br0">(</span><span class="br0">)</span></span></span> ，以共享模式锁定关联的互斥而不阻塞。</div>
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<div class="t-li2"><span class="t-li">6)</span> 假设调用方线程已在 <code>m</code> 上持有共享锁（即由 <code>lock_shared</code>、 <code>try_lock_shared</code>、 <code>try_lock_shared_for</code> 或 <code>try_lock_shared_until</code> 取得的锁）。若非如此则行为未定义。</div>
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<div class="t-li1"><span class="t-li">7)</span> 尝试通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">m.<span class="me1">try_lock_shared_for</span><span class="br0">(</span>timeout_duration<span class="br0">)</span></span></span> ，以共享模式锁定关联的互斥，这会阻塞直到经过指定的 <code>timeout_duration</code> 或取得锁，两者的先到来者。可能锁定长于 <code>timeout_duration</code> 。若 <code>Mutex</code> 不符合<a href="cpp-named_req-SharedTimedLockable.html"><span style="font-style:italic">可共享定时锁定</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(SharedTimedLockable)</span></a> 要求则行为未定义。</div>
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<div class="t-li1"><span class="t-li">8)</span> 尝试通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">m.<span class="me1">try_lock_shared_until</span><span class="br0">(</span>timeout_time<span class="br0">)</span></span></span> ，以共享模式锁定关联的互斥，这会阻塞直到抵达指定的 <code>timeout_time</code> 或取得锁，两者的先到来者。可能锁定长于到抵达 <code>timeout_time</code> 为止。若 <code>Mutex</code> 不符合<a href="cpp-named_req-SharedTimedLockable.html"><span style="font-style:italic">可共享定时锁定</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(SharedTimedLockable)</span></a> 要求则行为未定义。</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>以之初始化状态的另一 <code>shared_lock</code></td>
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<tr class="t-par">
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<td>m</td>
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<td>-</td>
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<td>关联到所的互斥，可选地获得其所有权</td>
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</tr>
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<tr class="t-par">
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<td>t</td>
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<td>-</td>
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<td>用于选择不同锁定策略的标签参数</td>
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</tr>
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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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</tr>
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<tr class="t-par">
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<td>timeout_time</td>
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<td>-</td>
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<td>要阻塞到的最大时间点</td>
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</tr>
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</table>
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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 <shared_mutex></span>
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<span class="co2">#include <iostream></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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<a href="cpp-thread-shared_timed_mutex.html"><span class="kw2158">std::<span class="me2">shared_timed_mutex</span></span></a> m<span class="sy4">;</span>
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<span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">10</span><span class="sy4">;</span>
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<span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">chrono</span><span class="sy4">;</span>
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<span class="kw4">void</span> read<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co1">// 两个线程都获得对整数 i 的访问</span>
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<a href="cpp-thread-shared_lock.html"><span class="kw2168">std::<span class="me2">shared_lock</span></span></a><span class="sy1"><</span><a href="cpp-thread-shared_timed_mutex.html"><span class="kw2158">std::<span class="me2">shared_timed_mutex</span></span></a><span class="sy1">></span> slk<span class="br0">(</span>m<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">"read i as "</span> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">"...<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="co1">// 此不同步</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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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"woke up...<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</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-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="br0">(</span>read<span class="br0">)</span>.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="br0">(</span>read<span class="br0">)</span>.<span class="me1">join</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">0</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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