[sane-devel] Fwd: Re: pthread_detach after pthread_join generates segfault
paddy-hack at member.fsf.org
Sat Sep 19 08:26:19 UTC 2015
# I had meant to send this to the list as well. It's a week later now
# and I have already requested merged the pu/ branch mentioned below.
I'm no pthread buff either, but
Jens-U. Mozdzen writes:
> Hi *,
> quoting Allan:
>> I'm no expert either, but your basic analysis seems correct- once you
>> have returned from pthread_join(), the thread is gone, and its return
>> value has been popped.
> that's indeed the way it works. Upon return of pthread_join(), the
> thread is *gone*... unless it returns with a non-zero rc.
>> I suppose it is possible that the pthread_join
>> could fail in a way that might leave the thread running, perhaps
>> because of a deadlock? In that case I suppose we could call
>> pthread_detatch only if there is an error?
> Other reasons to for pthread_join() to fail would be an already
> pending pthread_join() in a different thread.
> It's not necessary/valid to call pthread_detach() on all error cases -
> i.e. in case of ESRCH, there is no thread with that id. Calling
> pthread_detach() then will only return ESRCH itself, the same holds
> true for EINVAL.
The only valid, documented return value of pthread_join() where calling
pthread_detach() might make sense is EDEADLK. However, I am not sure
what the effect is of detaching the calling thread. Perhaps adding a
check for that makes sense.
I've pushed a proposed upgrade. If that looks okay, please merge. The
changes can be found at
> What doesn't fit the problem description is that calling
> pthread_detach() for an already terminated thread results in a segv.
> I'd rather have expected a return of ESRCH in such case. The only
> unspecified result (per man page) is for calling pthread_detach()
> multiple times on the same thread. Might this be the case here?
> quoting Gerhard
>> I wonder why it took 11 years to spot that ;)
> If it is a case of calling pthread_detach() multiple times, it may be
> because the code got compiled for a new platform. "undefined results"
> include causes a segv :D. Or maybe the pthread lib contains a bug,
> i.e. segfaulting on detaching a no longer existing thread, rather than
> returning ESRCH, or some race condition.
Hope this helps,
Olaf Meeuwissen, LPIC-2 FSF Associate Member since 2004-01-27
Support Free Software Support the Free Software Foundation
More information about the sane-devel