Question

Two Windows processes have memory mapped the same shared file. If the file consists of counters, is it appropriate to use the Interlocked* functions (like InterlockedIncrement) to update those counters? Will those synchronize access across processes? Or do I need to use something heavier, like a mutex? Or perhaps the shared-memory mechanism itself ensures consistent views.

Answer 1

From MSDN:

…

The Interlocked API

The interlocked functions provide a
simple mechanism for synchronizing
access to a variable that is shared by
multiple threads. They also perform
operations on variables in an atomic
manner. The threads of different
processes can use these functions if
the variable is in shared memory.

So, yes, it is safe with your shared memory approach.