std::atomic_flag_clear, std::atomic_flag_clear_explicit

 

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Defined in header <atomic>
void atomic_flag_clear( volatile std::atomic_flag* obj ) noexcept;	(1)	(since C++11)
void atomic_flag_clear( std::atomic_flag* obj ) noexcept;	(2)	(since C++11)
void atomic_flag_clear_explicit( volatile std::atomic_flag* obj,                                  std::memory_order order ) noexcept;	(3)	(since C++11)
void atomic_flag_clear_explicit( std::atomic_flag* obj,                                  std::memory_order order ) noexcept;	(4)	(since C++11)

Atomically changes the state of the std::atomic_flag pointed to by obj to clear (false).

1,2) The memory synchronization ordering is std::memory_order_seq_cst.

3,4) The memory synchronization ordering is order.

If order is one of std::memory_order_consume, std::memory_order_acquire and std::memory_order_acq_rel, the behavior is undefined.

Parameters

obj	-	pointer to std::atomic_flag to access
order	-	the memory synchronization ordering

Notes

std::atomic_flag_clear and std::atomic_flag_clear_explicit can be implemented as obj->clear() and obj->clear(order) respectively.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2138	C++11	order could be std::memory_order_consume	the behavior is undefined in this case

See also

atomic_flag (C++11)	the lock-free boolean atomic type (class)
atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C++11)(C++11)	atomically sets the flag to true and returns its previous value (function)
memory_order (C++11)	defines memory ordering constraints for the given atomic operation (enum)
C documentation for atomic_flag_clear, atomic_flag_clear_explicit