gprof with multithreaded applications
gprof is the GNU Profiler, a tool used when tracking which
functions are eating CPU in your program. Anyway, you should already be
familiar with it if you got interested in this page.
One problem with
gprof under certain kernels (such as Linux)
is that it doesn’t behave correctly with multithreaded applications. It
actually only profiles the main thread, which is quite useless.
There is an easy, but surprisingly not very widespread fix for this
gprof behaviour. Basically,
gprof uses the
ITIMER_PROF timer which makes the kernel deliver
a signal to the application whenever it expires. So we just need to pass this
timer data to all spawned threads.
It wouldn’t be too hard to put a call to
setitimer in each
function spawned by a thread, but I thought it would be more elegant to
implement a wrapper for
Daniel Jönsson enhanced my code so that it could be used in a preload library without having to modify the program. It can also be very useful for libraries that spawn threads without warning, such as libSDL. The result code is shown below and can be downloaded (gprof-helper.c):