weakCompareExchange(expected:desired:ordering:)
Perform an atomic weak compare and exchange operation on the current value, applying the memory ordering. This compare-exchange variant is allowed to spuriously fail; it is designed to be called in a loop until it indicates a successful exchange has happened.
Declaration
func weakCompareExchange(expected: consuming Value, desired: consuming Value, ordering: AtomicUpdateOrdering) -> (exchanged: Bool, original: Value)Parameters
- expected:
The expected current value.
- desired:
The desired new value.
- ordering:
The memory ordering to apply on this operation.
Return Value
A tuple (exchanged, original), where exchanged is true if the exchange was successful, and original is the original value.
Discussion
This operation performs the following algorithm as a single atomic transaction:
atomic(self) { currentValue in
let original = currentValue
guard original == expected else { return (false, original) }
currentValue = desired
return (true, original)
}