time used by a thread

[Stephen Montgomery-Smith]

I want to use getrusage to see how much time a program is using.  But 
this is a multithreaded program, and I just want the time taken by that 
particular thread!

I know this info must be available somewhere, because top -H seems to 
provide it.  But getrusage seems to give the total rusage for the whole 
program, not just the thread.

Any ideas?  I would especially appreciate a portable solution that works 
for OS other than FreeBSD (e.g. linux, etc as well).

I tried "apropos thread | grep usage".