157 lines
14 KiB
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157 lines
14 KiB
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<title>std::recursive_timed_mutex::try_lock_for</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::recursive_timed_mutex::</span>try_lock_for</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-recursive_timed_mutex.html">recursive timed mutex</a></span></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> Rep, <span class="kw1">class</span> Period <span class="sy1">></span><br />
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<span class="kw4">bool</span> try_lock_for<span class="br0">(</span> <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></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>尝试锁互斥。阻塞直到经过指定的 <code>timeout_duration</code> 或得到锁，取决于何者先到来。成功获得锁时返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ， 否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<p>若 <code>timeout_duration</code> 小于或等于 <code>timeout_duration.zero()</code> ，则函数表现同 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-try_lock.html">try_lock()</a></span> 。</p>
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<p>由于调度或资源争议延迟，此函数可能阻塞长于 <code>timeout_duration</code> 。</p>
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<p>标准推荐用 <a href="cpp-chrono-steady_clock.html"><tt>steady_clock</tt></a> 度量时长。若实现用 <a href="cpp-chrono-system_clock.html"><tt>system_clock</tt></a> 代替，则等待时间亦可能对时钟调整敏感。</p>
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<p>同 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-try_lock.html">try_lock()</a></span> ，允许此函数虚假地失败并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，即使在 <code>timeout_duration</code> 中某点互斥不为任何线程所锁定。</p>
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<p>若此操作返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则同一互斥上先前的 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-unlock.html">unlock()</a></span> 调用<i>同步于</i>（定义于 <span class="t-lc"><a href="cpp-atomic-memory_order.html">std::memory_order</a></span> ）它。</p>
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<p>线程可以在递归互斥上重复调用 <code>try_lock_for</code> 。对 <code>try_lock_for</code> 的成功调用增加所有权计数：仅在线程调用 <span class="t-lc"><a href="cpp-thread-recursive_timed_mutex-unlock.html">unlock</a></span> 匹配次数后才会释放互斥。</p>
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<p>所有权等级数的最大值是未指定的。若超出此值，则到 <code>try_lock_for</code> 的调用将返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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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>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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<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>若成功获得锁则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>执行期间时钟、时间点或时长可能抛出的异常（标准库提供的时钟、时间点和时长决不抛出）</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <mutex></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <sstream></span>
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<a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a> cout_mutex<span class="sy4">;</span> <span class="co1">// 控制到 std::cout 的访问</span>
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<a href="cpp-thread-timed_mutex.html"><span class="kw2156">std::<span class="me2">timed_mutex</span></span></a> mutex<span class="sy4">;</span>
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<span class="kw4">void</span> job<span class="br0">(</span><span class="kw4">int</span> id<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">using</span> Ms <span class="sy1">=</span> <a href="cpp-chrono-duration.html"><span class="kw996">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">milliseconds</span></span></a><span class="sy4">;</span>
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<a href="cpp-io-basic_ostringstream.html"><span class="kw1736">std::<span class="me2">ostringstream</span></span></a> stream<span class="sy4">;</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">3</span><span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>mutex.<span class="me1">try_lock_for</span><span class="br0">(</span>Ms<span class="br0">(</span><span class="nu0">100</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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stream <span class="sy1"><<</span> <span class="st0">"success "</span><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>Ms<span class="br0">(</span><span class="nu0">100</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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mutex.<span class="me1">unlock</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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stream <span class="sy1"><<</span> <span class="st0">"failed "</span><span class="sy4">;</span>
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<span class="br0">}</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>Ms<span class="br0">(</span><span class="nu0">100</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<a href="cpp-thread-lock_guard.html"><span class="kw2166">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="cpp-thread-mutex.html"><span class="kw2154">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lock<span class="br0">(</span>cout_mutex<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">"["</span> <span class="sy1"><<</span> id <span class="sy1"><<</span> <span class="st0">"] "</span> <span class="sy1"><<</span> stream.<span class="me1">str</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>
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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-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a><span class="sy1">></span> threads<span class="sy4">;</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">4</span><span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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threads.<span class="me1">emplace_back</span><span class="br0">(</span>job, i<span class="br0">)</span><span class="sy4">;</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">auto</span><span class="sy3">&</span> i<span class="sy4">:</span> threads<span class="br0">)</span> <span class="br0">{</span>
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i.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</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">[0] failed failed failed
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[3] failed failed success
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[2] failed success failed
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[1] success failed success</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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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_mutex-lock.html"><span class="t-lines"><span>lock</span></span></a></div>
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</div>
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</td>
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<td>锁定互斥，若互斥不可用则阻塞<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_mutex-try_lock.html"><span class="t-lines"><span>try_lock</span></span></a></div>
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</div>
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</td>
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<td>尝试锁定互斥，若互斥不可用则返回<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_mutex-try_lock_until.html"><span class="t-lines"><span>try_lock_until</span></span></a></div>
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</div>
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</td>
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<td>尝试锁定互斥，若直至抵达指定时间点互斥不可用则返回<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-recursive_timed_mutex-unlock.html"><span class="t-lines"><span>unlock</span></span></a></div>
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</div>
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</td>
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<td>解锁互斥<br />
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<span class="t-mark">(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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