Re: pthread_join problem

[Ross Johnson <Ross dot Johnson at homemail dot com dot au>]

Stefan Eilemann wrote:
> Hello,
>
> I am in the situation that a pthread_join does not return, even
> though the thread has called pthread_exit.
>
> I read the cleanup notes, but I think it does not apply here.
>
> I am using the C cleanup code. One thread calls pthread_exit,
> the other phtread_join. I've verified that the thread calling
> pthread_exit does the longjmp to the thread start code, which
> calls _endthreadex.
>
> The main thread calling pthread_join does hang in
> WaitForMultipleObjects.
>
> The problem only occurs when I am using some unrelated(?)
> external code (the Mellanox SDP Infiniband implementation),
> so it could be caused by that, or just be a race appearing
> with this code.
>
> There are other pthreads in my application, which terminate
> correctly with pthread_exit/pthread_join. Only one thread -
> the network receive thread ;)- does exhibit the problem.
>
> Do you have an idea what could be the cause of this problem?
> Anything else I could try to find the problem?
One thing that comes to mind that seems to fit the evidence assumes that 
the external code that you mentioned is a DLL and it executes it's own 
dllMain routine which somehow interferes with pthread-win32's thread 
exit cleanup. This would be occurring after _endthreadex() is called, 
which you've verified is called.

I don't know how Win32 determines which and in what order these 
dllMain's are called (is it the order the DLLs are loaded?), but 
pthreads-win32 does rely on this mechanism to do some final cleanup and 
status setting for each 'POSIX' thread, and if this doesn't get done I 
imagine it's possible you would see symptoms like this.

Pthreads-win32's dllMain() calls pthread_win32_thread_detach_np() in 
pthread_win32_attach_detach_np.c. To verify that this is happening you 
could set up a thread-specific data key and give it a destructor 
routine, have your problem thread set it to a non-null value, and then 
see if the destructor routine is called.

Regards.
Ross
> Best Regards,
>
> Stefan.
>
> PS: I've tested the Win64 version, and it works like a charm.