Same as the _InterlockedCompareExchange_acq function except that those parts of the algorithm that are marked "Atomic" are performed by the cmpxchg4.rel instruction with release ordering semantics; that is, the memory read/write is made visible after all previous memory accesses of the Destination by other processors. Syntax: unsigned __int64 _InterlockedCompareExchange_rel (volatile unsigned int *Destination, unsigned __int64 Newval, unsigned __int64 Comparand);