The timed mutex types are the standard library types std::timed_mutex and std::recursive_timed_mutex. They shall 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 ([time.duration]), and abs_time denotes an object of an instantiation of time_point ([time.point]).
The timed mutex types shall meet the TimedLockable requirements ([thread.req.lockable.timed]).
The expression m.try_lock_for(rel_time) shall be well-formed and have the following semantics:
Requires: If the tick period of rel_time is not exactly convertible to the native tick period, the duration shall be rounded up to the nearest native tick period. If m is of type std::timed_mutex, the calling thread does not own the mutex.
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 shall return within the timeout specified by rel_time only if it has obtained ownership of the mutex object. [ Note: 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 ]
Return type: bool
Returns: true if ownership was obtained, otherwise false.
Synchronization: If try_lock_for() returns true, prior unlock() operations on the same object synchronize with ([intro.multithread]) this operation.
Throws: Nothing.
The expression m.try_lock_until(abs_time) shall be well-formed and have the following semantics:
Requires: If m is of type std::timed_mutex, the calling thread does not own the mutex.
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 shall return before the absolute timeout ([thread.req.timing]) specified by abs_time only if it has obtained ownership of the mutex object. [ Note: 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 ]
Return type: bool
Returns: true if ownership was obtained, otherwise false.
Synchronization: If try_lock_until() returns true, prior unlock() operations on the same object synchronize with ([intro.multithread]) this operation.
Throws: Nothing.
namespace std {
class timed_mutex {
public:
timed_mutex();
~timed_mutex();
timed_mutex(const timed_mutex&) = delete;
timed_mutex& operator=(const timed_mutex&) = delete;
void lock();
bool 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();
typedef implementation-defined native_handle_type; // See [thread.req.native]
native_handle_type native_handle(); // See [thread.req.native]
};
}
The class timed_mutex provides a non-recursive mutex with exclusive ownership semantics. If one thread owns a timed_mutex object, attempts by another thread to acquire ownership of that object will fail (for try_lock()) or block (for lock(), try_lock_for(), and try_lock_until()) until the owning thread has released ownership with a call to unlock() or the call to try_lock_for() or try_lock_until() times out (having failed to obtain ownership).
The class timed_mutex shall satisfy all of the TimedMutex requirements ([thread.timedmutex.requirements]). It shall be a standard-layout class (Clause [class]).
namespace std {
class recursive_timed_mutex {
public:
recursive_timed_mutex();
~recursive_timed_mutex();
recursive_timed_mutex(const recursive_timed_mutex&) = delete;
recursive_timed_mutex& operator=(const recursive_timed_mutex&) = delete;
void lock();
bool try_lock() noexcept;
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();
typedef implementation-defined native_handle_type; // See [thread.req.native]
native_handle_type native_handle(); // See [thread.req.native]
};
}
The class recursive_timed_mutex provides a recursive mutex with exclusive ownership semantics. If one thread owns a recursive_timed_mutex object, attempts by another thread to acquire ownership of that object will fail (for try_lock()) or block (for lock(), try_lock_for(), and try_lock_until()) until the owning thread has completely released ownership or the call to try_lock_for() or try_lock_until() times out (having failed to obtain ownership).
The class recursive_timed_mutex shall satisfy all of the TimedMutex requirements ([thread.timedmutex.requirements]). It shall be a standard-layout class (Clause [class]).
A thread that owns a recursive_timed_mutex object may acquire additional levels of ownership by calling lock(), try_lock(), try_lock_for(), or try_lock_until() on that object. It is unspecified how many levels of ownership may be acquired by a single thread. If a thread has already acquired the maximum level of ownership for a recursive_timed_mutex object, additional calls to try_lock(), try_lock_for(), or try_lock_until() shall fail, and additional calls to lock() shall throw an exception of type system_error. A thread shall call unlock() once for each level of ownership acquired by calls to lock(), try_lock(), try_lock_for(), and try_lock_until(). Only when all levels of ownership have been released may ownership of the object be acquired by another thread.