Let me do a shot in the dark. After much contemplation and searching the net plus the way you described your problem, I think you mean a type of data storage using mapped values. Is this correct? If it's not correct, then you need to tell us what you mean by map file? Is it an actual map like what we use to find our way in the world? Quake uses map files but I doubt it's that. In any case, there's many cases as what a map file could be. You're going to have to be very specific as to what you mean.
OP is clearly talking about a memory mapped file (or filemapping as MS calls it), as his description talks about multiple threads wanting to access the same data.I was able to find this. Maybe it helps as it uses some terminology and variables/functions that are specific to mapping files in linux, so perhaps that can help with the searches.