[Arnavion]

InterlockedCompareExchange is supposed to be an atomic compare-and-swap API. "Compare-and-swap" means the swap only occurs if the comparison succeeded, ie if the previous value of `*dest` was `compare`, then `xchg` is written to `*dest`. "Atomic" means that another thread cannot make changes between the two steps; if another thread did come in and modified the value between the comparison and the swap, the swap would not occur.

A proper implementation would use some kind of locking in the worst case, but usually would rely on hardware features to provide this atomicity. For example, on x86 this is done by the CMPXCHG family of instructions.

The mock implementation is not atomic. Another thread can change the value between the comparison and swap and the swap will still happen. As for the fix, there might be an intrinsic for it in the W95 SDK, or worst case an inline assembly implementation using CMPXCHG would do the job.