StackThreads/MP: version 0.77 User's Guide

3.6.1: Examine Current Stack Size

        long st_stack_used_bytes()

returns the distance between the current stack top and the stack bottom. It specifically does not return the stack limit, but return the size of the stack currently occupied. The stack size increases when a procedure is called and may decrease when a procedure is returned or ST_POLLING or ST_FREE_STACK is called.