std::atomic_flag_clear, std::atomic_flag_clear_explicit

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atomic_flag_clearatomic_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

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)

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

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