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    std::atomic_flag_clear, std::atomic_flag_clear_explicit

    From cppreference.com
     
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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

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