33 Concurrency support library [thread]

33.6 Mutual exclusion [thread.mutex]

33.6.4 Mutex requirements [thread.mutex.requirements]

33.6.4.5 Shared timed mutex types [thread.sharedtimedmutex.requirements]

33.6.4.5.1 General [thread.sharedtimedmutex.requirements.general]

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The standard library type shared_timed_mutex is a shared timed mutex type.
Shared timed mutex types meet the requirements of timed mutex types ([thread.timedmutex.requirements]), shared mutex types ([thread.sharedmutex.requirements]), and additionally meet the requirements set out below.
In this description, m denotes an object of a shared timed mutex type, rel_time denotes an object of an instantiation of duration ([time.duration]), and abs_time denotes an object of an instantiation of time_point ([time.point]).
[Note 1: 
The shared timed mutex types meet the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]).
— end note]
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The expression m.try_lock_shared_for(rel_time) is well-formed and has the following semantics:
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Preconditions: The calling thread has no ownership of the mutex.
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Effects: Attempts to obtain shared lock ownership for the calling thread within the relative timeout ([thread.req.timing]) specified by rel_time.
If the time specified by rel_time is less than or equal to rel_time.zero(), the function attempts to obtain ownership without blocking (as if by calling try_lock_shared()).
The function returns within the timeout specified by rel_time only if it has obtained shared ownership of the mutex object.
[Note 2: 
As with try_lock(), there is no guarantee that ownership will be obtained if the lock is available, but implementations are expected to make a strong effort to do so.
— end note]
If an exception is thrown then a shared lock has not been acquired for the current thread.
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Synchronization: If try_lock_shared_for() returns true, prior unlock() operations on the same object synchronize with ([intro.multithread]) this operation.
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Return type: bool.
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Returns: true if the shared lock was acquired, otherwise false.
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Throws: Timeout-related exceptions ([thread.req.timing]).
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The expression m.try_lock_shared_until(abs_time) is well-formed and has the following semantics:
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Preconditions: The calling thread has no ownership of the mutex.
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Effects: The function attempts to obtain shared ownership of the mutex.
If abs_time has already passed, the function attempts to obtain shared ownership without blocking (as if by calling try_lock_shared()).
The function returns before the absolute timeout ([thread.req.timing]) specified by abs_time only if it has obtained shared ownership of the mutex object.
[Note 3: 
As with try_lock(), there is no guarantee that ownership will be obtained if the lock is available, but implementations are expected to make a strong effort to do so.
— end note]
If an exception is thrown then a shared lock has not been acquired for the current thread.
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Synchronization: If try_lock_shared_until() returns true, prior unlock() operations on the same object synchronize with ([intro.multithread]) this operation.
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Return type: bool.
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Returns: true if the shared lock was acquired, otherwise false.
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Throws: Timeout-related exceptions ([thread.req.timing]).