Since parts of the MPI library may themselves be implemented using more basic MPI functions (e.g. a portable implementation of the collective operations implemented using point to point communications), there is potential for profiling functions to be called from within an MPI function which was called from a profiling function. This could lead to ``double counting'' of the time spent in the inner routine. Since this effect could actually be useful under some circumstances (e.g. it might allow one to answer the question ``How much time is spent in the point to point routines when they're called from collective functions ?''), the MPI Forum decided not to enforce any restrictions on the author of the MPI library which would overcome this. Therefore, the author of the profiling library should be aware of this problem, and guard against it. In a single threaded world this is easily achieved through use of a static variable in the profiling code which remembers if you are already inside a profiling routine. It becomes more complex in a multi-threaded environment (as does the meaning of the times recorded!)