Keeping memory mapped files from growing too large

Question

I'm wanting to use memory-mapped IO to establish communications between two applications of mine (primarily to avoid the problem of sockets tending to leak to other computers on the network). However, one issue I am concerned about is storage space: as I continue writing commands to the file, that file is only going to get larger. Granted, most of the commands are short and it would take a few days of constant runtime for it to become a problem, but I would like to avoid it all the same. Is there a good way for me to periodically clear the file of "old" messages that my recipient application has already read, thus reclaiming disc storage space?