std::atomic_ref<T>::fetch_or

T fetch_or( T arg, 
            std::memory_order order = std::memory_order_seq_cst ) const noexcept;

(since C++20)
(member only of atomic_ref<Integral> template specialization)

Atomically replaces the current value of the referenced object with the result of bitwise OR of the value and arg. This operation is a read-modify-write operation. Memory is affected according to the value of order.

Parameters

arg	-	the other argument of bitwise OR
order	-	memory order constraints to enforce

Return value

The value of the referenced object, immediately preceding the effects of this function.

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