how to determine a programs memory usage at runtime?

Hi all, Is there any way I can find out or estimate the memory size of a program while it is executing? This may very well be problematic and system specific, but I haven't a clue where to look. Perhaps there is a posix interface I am missing? Or a hook into the runtime? Why do I want to know this? I'm experimenting with interleaving the execution of buddha's debugging algorithm with the execution of the debuggee. Assume for the moment that the debuggee runs in one thread and the debugger runs in another. One strategy I want to test is running the debuggee until some threshold of memory has been used, suspend the debuggee and jump to the debugger, then possibly back again. Cheers, Bernie.