kill(pid,0) sends a signal or not?

[Daniel Eischen]

On Sun, 20 Jun 2004, Sean McNeil wrote:

> I'm trying to trace down an issue with kse threads and firefox.  There
> is an odd "trick" I haven't seen before:
> 
>  // kill(pid,0) is a neat trick to check if a
>  // process exists
>  if (kill(pid, 0) == 0 || errno != ESRCH)
> 
> Does this really work?  It is kind of odd that it I appear to get a
> signal (if the traceback is accurate) with the signal set to 0:
> 
> #10 0x0000000202bc7a80 in thr_resume_wrapper (sig=0, siginfo=0x4,
>     ucp=0x7fffffffd4c0) at /usr/src/lib/libpthread/thread/thr_kern.c:1112
> 
> This later causes a sig 11 and the program core dumps.
> 
> Any info on how threads are suppose to behave when a process does a
> kill(pid,0) would be greatly appreciated.

kill(pid, 0) shouldn't result in a signal.  libpthread doesn't do
anything with kill() and the kernel shouldn't cause a signal for 0
either.  What does ktrace show?

-- 
Dan Eischen