[sane-devel] pthread_detach after pthread_join generates segfault

m. allan noah kitno455 at gmail.com
Wed Aug 26 00:53:11 UTC 2015

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. 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?

Gerhard- do you remember anything about commit
0fb34bb098f1cbdd9d154328cb7f9d45ed8f6256 ?


On Tue, Aug 25, 2015 at 5:36 PM, Luiz Angelo Daros de Luca
<luizluca at gmail.com> wrote:
> Hello,
> I was getting a segfault for sane-backends when using device sane-test. This
> happened when I compiled sane with uclibc or musl (on openwrt).
> I debugged the problem and traced it to sanei_thread_waitpid (at
> sanei/sanei_thread.c). It seems that calling pthread_detach after someone
> already did a pthread_join causes a segfault.
> I'm no pthread expert but I guess that after a pthread_join, the thread
> becomes "detached" and "terminated".
> And, according to man page PTHREAD_DETACH(3):
> "Attempting to detach an already detached thread results in unspecified
> behavior."
> I simply removed these detach lines in order to solve my problem. What would
> be the correct fix? Is there any case when join fails and detach is still
> valid? I checked error codes and only EDEADLK(when the thread is already
> waiting for the caller) and EINVAL (when three is another thread is already
> waiting for it) are possible situations when detach might do something. Are
> they possible in sane thread usage? If so, I guess detach might only be
> called when one of the possible fails of join happens.
> Regards,
> Luiz Angelo Daros de Luca
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