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Re: threading question

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On 12/14/2011 9:48 AM, Rainer Weikusat wrote:
> Bill M<wpmccormick@just_about_everywhere.com>  writes:
>> If I ctrl-c kill an daemon type application, will child threads
>> created by the application also be killed or will they become zombie
>> threads?
>
> There is no such thing as 'a zombie thread', at least not in the sense
> you are using the term (technically, a non-detached thread which has
> exited will become 'a zombie thread' because the return value will be
> kept somewhere until [if ever] another thread calls pthread_join in
> order to receive that. While this is similar to 'zombie processes', I
> haven't seen the term 'zombie thread' anywhere so far).

Right, so if I have a some program ...

pthread_create(&thread, ... )

while(some_condition)
{
   ...
}

pthread_kill(thread, sig);
pthread_join(thread, *retval);

exit(0);

... and the program is killed, with ctrl-c or some other signal, then 
the pthread_join is never called. So I *think* I need to trap signals 
and exit the while loop so I can clean up the thread. Stop me here if 
I'm not right.

 From the Sigaction man page:
POSIX.1-1990 disallowed setting the action for SIGCHLD to SIG_IGN. 
POSIX.1-2001  allows  this possibility,  so  that  ignoring  SIGCHLD 
can be used to prevent the creation of zombies (see wait(2)). 
Nevertheless, the historical BSD and System V behaviors for ignoring 
SIGCHLD differ, so  that the only completely portable method of ensuring 
that terminated children do not become zombies is to catch the SIGCHLD 
signal and perform a wait(2) or similar.

So, the way I understand that is that I need to catch SIGCHLD (and 
SIG_IGN?) and kill the thread, then wait for it to complete with the 
join. So if that's all correct, what sig should be sent with pthread_kill?

Obviously, I'm breaking new ground for myself here, so please let me 
know if should be considering something else.


Thanks,

Bill

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threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-14 09:05 -0600
  Re: threading question Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-12-14 15:48 +0000
    Re: threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-14 10:26 -0600
      Re: threading question Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-12-14 16:33 +0000
        Re: threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-14 11:12 -0600
          Re: threading question Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-12-14 18:10 +0000
            Re: threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-14 13:28 -0600
          Re: threading question Richard Kettlewell <rjk@greenend.org.uk> - 2011-12-14 18:30 +0000
          Re: threading question Mark <i@dontgetlotsofspamanymore.invalid> - 2011-12-15 15:19 +0000
            Re: threading question Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-12-15 15:42 +0000
            Re: threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-15 18:50 -0600
              Re: threading question Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-12-16 03:40 +0000
                Re: threading question Bill M <wpmccormick@just_about_everywhere.com> - 2011-12-16 08:23 -0600

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