_InterlockedCompareExchange_acq

 Atomically compares and exchanges the value specified by the first
 argument (a 64-bit pointer).  This function maps to the
 cmpxchg4.acq instruction with appropriate setup.

 The value at *Destination is compared with the value specified by
 Comparand.  If they are equal, Newval is written to *Destination,
 and Oldval is returned.  The exchange will have taken place if the
 value returned is equal to the Comparand.  The following algorithm
 is used:

 ar.ccv = Comparand;
 Oldval = *Destination;         //Atomic
 if (ar.ccv == *Destination)    //Atomic
     *Destination = Newval;     //Atomic
 return Oldval;

 Those parts of the algorithm marked "Atomic" are performed
 atomically by the cmpxchg4.acq instruction.  This instruction has
 acquire ordering semantics; that is, the memory read/write is made
 visible prior to all subsequent data memory accesses of the
 Destination by other processors.

 Syntax:

      unsigned __int64 _InterlockedCompareExchange_acq (volatile 
      unsigned int *Destination, unsigned __int64 Newval, unsigned
      __int64 Comparand);