Re: Trying to join an already exited pthread

[Garrett Cooper <youshi10_(_at_)_u_(_dot_)_washington_(_dot_)_edu>]

Garrett Cooper wrote:
> Garrett Cooper wrote:
> > On Feb 7, 2007, at 1:51 PM, Steve Watt wrote:
> >
> > > In <Pine_(_dot_)_LNX_(_dot_)_4_(_dot_)_43_(_dot_)_0702071314560_(_dot_)_22034_(_at_)_hymn08_(_dot_)_u_(_dot_)_washington_(_dot_)_edu>,
> > >  <youshi10_(_at_)_u_(_dot_)_washington_(_dot_)_edu> wrote:
> > > > Just wondering:
> > > >
> > > > If I was to try and join a pthread that already exited, would there 
> > > > be an error
> > > > message output and/or errno set to an error value, or would a system 
> > > > hang?
> > >
> > > Was the thread created with detach state set PTHREAD_CREATE_DETACHED or
> > > PTHREAD_CREATE_JOINABLE?  If it was PTHREAD_CREATE_JOINABLE, has the
> > > thread already been joined?
> > >
> > > You should be able to join a thread that was created joinable, only 
> > > once.
> > > If you join it again, or join a thread that was created detached, the
> > > results are unspecified in POSIX.  There is an error status that may
> > > be returned, but it may do other bad things to your system.
> > >
> > > Note that pthread_join doesn't set errno; it returns an error value
> > > directly.  I would never expect the system to hang, though the 
> > > application
> > > might.  If your application is hanging, make sure that you're not trying
> > > to call pthread_join from within a signal handler.
> > >
> > > > It this variable on Unix OSes?
> > >
> > > That the results are unspecified?  No.  What "unspecified" means?
> > > Absolutely.
> > > --Steve Watt KD6GGD  PP-ASEL-IA          ICBM: 121W 56' 57.5" / 37N 
> > > 20' 15.3"
> > >  Internet: steve @ Watt.COM                      Whois: SW32-ARIN
> > >    Free time?  There's no such thing.  It just comes in varying 
> > > prices...
> >
> >     I asked this because I was short on time and so was the person who 
> > asked me earlier. I'm going to try giving the pthread exit and join a 
> > shot just to see whether or not this is true or not and then I'll 
> > report my results to the list.
> >     Thanks for the insight though--hopefully my results will yield a 
> > solid positive or negative to this being a problem.
> > -Garrett
>
> Under Suse Linux there were absolutely no errors when I tried to do 
> this. I'll post a code snippet later.
> -Garrett

Ok, here's a link to my code:

http://students.washington.edu/youshi10/posted/thread_test.c

My results (FreeBSD):

[root_(_at_)_hoover /home/gcooper]# ./tt
Thread join detached
Thread kill detached
Joined thread yielded error code: 2
Trying to join the already joined thread yields error code: 0

My results (Suse Linux):

# ./tt
Thread join detached
Thread kill detached
Joined thread yielded error code: 0
Trying to join the already joined thread yields error code: 0

That was sure interesting.. is it supposed to error out or was it the 
remnant of an old error call?

Probably the latter, but I was just curious..

-Garrett
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