202 lines
9.1 KiB
Markdown
202 lines
9.1 KiB
Markdown
[thread.sharedtimedmutex.requirements]
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# 32 Concurrency support library [[thread]](./#thread)
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## 32.6 Mutual exclusion [[thread.mutex]](thread.mutex#thread.sharedtimedmutex.requirements)
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### 32.6.4 Mutex requirements [[thread.mutex.requirements]](thread.mutex.requirements#thread.sharedtimedmutex.requirements)
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#### 32.6.4.5 Shared timed mutex types [thread.sharedtimedmutex.requirements]
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#### [32.6.4.5.1](#general) General [[thread.sharedtimedmutex.requirements.general]](thread.sharedtimedmutex.requirements.general)
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[1](#general-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L7987)
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The standard library type shared_timed_mutex is a[*shared timed mutex type*](#def:shared_timed_mutex_type "32.6.4.5.1 General [thread.sharedtimedmutex.requirements.general]")[.](#general-1.sentence-1)
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Shared timed mutex types meet the requirements of
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timed mutex types ([[thread.timedmutex.requirements]](thread.timedmutex.requirements "32.6.4.3 Timed mutex types")),
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shared mutex types ([[thread.sharedmutex.requirements]](thread.sharedmutex.requirements "32.6.4.4 Shared mutex types")), and additionally
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meet the requirements set out below[.](#general-1.sentence-2)
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In this description,m denotes an object of a shared timed mutex type,rel_time denotes an object of an instantiation ofduration ([[time.duration]](time.duration "30.5 Class template duration")), andabs_time denotes an object of an instantiation of[time_point](time.point "30.6 Class template time_point [time.point]")[.](#general-1.sentence-3)
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[*Note [1](#general-note-1)*:
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The shared timed mutex types meet the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements"))[.](#general-1.sentence-4)
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â *end note*]
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[2](#general-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8003)
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The expression m.try_lock_shared_for(rel_time) is well-formed and
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has the following semantics:
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[3](#general-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8007)
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*Preconditions*: The calling thread has no ownership of the mutex[.](#general-3.sentence-1)
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[4](#general-4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8011)
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*Effects*: Attempts to obtain
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shared lock ownership for the calling thread within the relative
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timeout ([[thread.req.timing]](thread.req.timing "32.2.4 Timing specifications")) specified by rel_time[.](#general-4.sentence-1)
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If the time
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specified by rel_time is less than or equal to rel_time.zero(),
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the function attempts to obtain ownership without blocking (as if by callingtry_lock_shared())[.](#general-4.sentence-2)
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The function returns within the timeout
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specified by rel_time only if it has obtained shared ownership of the
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mutex object[.](#general-4.sentence-3)
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[*Note [2](#general-note-2)*:
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As with try_lock(), there is no guarantee that
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ownership will be obtained if the lock is available, but implementations are
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expected to make a strong effort to do so[.](#general-4.sentence-4)
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â *end note*]
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If an exception is thrown then a shared lock has not been acquired for
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the current thread[.](#general-4.sentence-5)
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[5](#general-5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8029)
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*Synchronization*: If try_lock_shared_for() returns true, priorunlock() operations on the same object synchronize
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with ([[intro.multithread]](intro.multithread "6.10.2 Multi-threaded executions and data races")) this operation[.](#general-5.sentence-1)
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[6](#general-6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8035)
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*Return type*: bool[.](#general-6.sentence-1)
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[7](#general-7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8038)
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*Returns*: true if the shared lock was acquired, otherwise false[.](#general-7.sentence-1)
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[8](#general-8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8042)
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*Throws*: Timeout-related exceptions ([[thread.req.timing]](thread.req.timing "32.2.4 Timing specifications"))[.](#general-8.sentence-1)
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[9](#general-9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8047)
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The expression m.try_lock_shared_until(abs_time) is well-formed
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and has the following semantics:
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[10](#general-10)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8051)
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*Preconditions*: The calling thread has no ownership of the mutex[.](#general-10.sentence-1)
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[11](#general-11)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8055)
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*Effects*: The function attempts to obtain shared ownership of the mutex[.](#general-11.sentence-1)
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Ifabs_time has already passed, the function attempts to obtain shared
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ownership without blocking (as if by calling try_lock_shared())[.](#general-11.sentence-2)
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The
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function returns before the absolute timeout ([[thread.req.timing]](thread.req.timing "32.2.4 Timing specifications"))
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specified by abs_time only if it has obtained shared ownership of the
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mutex object[.](#general-11.sentence-3)
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[*Note [3](#general-note-3)*:
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As with try_lock(), there is no guarantee that
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ownership will be obtained if the lock is available, but implementations are
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expected to make a strong effort to do so[.](#general-11.sentence-4)
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â *end note*]
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If an exception is thrown then a shared lock has not been acquired for
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the current thread[.](#general-11.sentence-5)
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[12](#general-12)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8071)
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*Synchronization*: If try_lock_shared_until() returns true, priorunlock() operations on the same object synchronize
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with ([[intro.multithread]](intro.multithread "6.10.2 Multi-threaded executions and data races")) this operation[.](#general-12.sentence-1)
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[13](#general-13)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8077)
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*Return type*: bool[.](#general-13.sentence-1)
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[14](#general-14)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8080)
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*Returns*: true if the shared lock was acquired, otherwise false[.](#general-14.sentence-1)
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[15](#general-15)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8084)
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*Throws*: Timeout-related exceptions ([[thread.req.timing]](thread.req.timing "32.2.4 Timing specifications"))[.](#general-15.sentence-1)
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#### [32.6.4.5.2](#thread.sharedtimedmutex.class) Class shared_timed_mutex [[thread.sharedtimedmutex.class]](thread.sharedtimedmutex.class)
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[ð](#lib:shared_timed_mutex)
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namespace std {class shared_timed_mutex {public: shared_timed_mutex(); ~shared_timed_mutex();
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shared_timed_mutex(const shared_timed_mutex&) = delete;
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shared_timed_mutex& operator=(const shared_timed_mutex&) = delete; // exclusive ownershipvoid lock(); // blockingbool try_lock(); template<class Rep, class Period>bool try_lock_for(const chrono::duration<Rep, Period>& rel_time); template<class Clock, class Duration>bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); void unlock(); // shared ownershipvoid lock_shared(); // blockingbool try_lock_shared(); template<class Rep, class Period>bool try_lock_shared_for(const chrono::duration<Rep, Period>& rel_time); template<class Clock, class Duration>bool try_lock_shared_until(const chrono::time_point<Clock, Duration>& abs_time); void unlock_shared(); };}
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[1](#thread.sharedtimedmutex.class-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8123)
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The class shared_timed_mutex provides a non-recursive mutex with shared
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ownership semantics[.](#thread.sharedtimedmutex.class-1.sentence-1)
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[2](#thread.sharedtimedmutex.class-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8127)
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The class shared_timed_mutex meets
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all of the shared timed mutex requirements ([thread.sharedtimedmutex.requirements])[.](#thread.sharedtimedmutex.class-2.sentence-1)
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It is a standard-layout class ([[class.prop]](class.prop "11.2 Properties of classes"))[.](#thread.sharedtimedmutex.class-2.sentence-2)
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[3](#thread.sharedtimedmutex.class-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8132)
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The behavior of a program is undefined if
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- [(3.1)](#thread.sharedtimedmutex.class-3.1)
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it destroys a shared_timed_mutex object owned by any thread,
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- [(3.2)](#thread.sharedtimedmutex.class-3.2)
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a thread attempts to recursively gain any ownership of a shared_timed_mutex, or
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- [(3.3)](#thread.sharedtimedmutex.class-3.3)
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a thread terminates while possessing any ownership of a shared_timed_mutex[.](#thread.sharedtimedmutex.class-3.sentence-1)
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