33 Concurrency support library [thread]

33.6 Mutual exclusion [thread.mutex]

33.6.4 Mutex requirements [thread.mutex.requirements]

33.6.4.3 Timed mutex types [thread.timedmutex.requirements]

33.6.4.3.1 General [thread.timedmutex.requirements.general]

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The timed mutex types are the standard library types timed_mutex, recursive_timed_mutex, and shared_timed_mutex.
They meet the requirements set out below.
In this description, m denotes an object of a mutex type, rel_time denotes an object of an instantiation of duration, and abs_time denotes an object of an instantiation of time_point.
[Note 1: 
The timed mutex types meet the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).
— end note]
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The expression m.try_lock_for(rel_time) is well-formed and has the following semantics:
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Preconditions: If m is of type timed_mutex or shared_timed_mutex, the calling thread does not own the mutex.
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Effects: The function attempts to obtain ownership of the mutex 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()).
The function returns within the timeout specified by rel_time only if it has obtained 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]
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Synchronization: If try_lock_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 ownership was obtained, otherwise false.
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Throws: Timeout-related exceptions ([thread.req.timing]).
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The expression m.try_lock_until(abs_time) is well-formed and has the following semantics:
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Preconditions: If m is of type timed_mutex or shared_timed_mutex, the calling thread does not own the mutex.
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Effects: The function attempts to obtain ownership of the mutex.
If abs_time has already passed, the function attempts to obtain ownership without blocking (as if by calling try_lock()).
The function returns before the absolute timeout ([thread.req.timing]) specified by abs_time only if it has obtained 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]
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Synchronization: If try_lock_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 ownership was obtained, otherwise false.
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Throws: Timeout-related exceptions ([thread.req.timing]).