Re: Do gui applications always have 2 threads ?

[David Chisnall]

On 22 Jan 2011, at 20:54, Philippe Roussel wrote:

> Hi all,
> 
> In trying to understand why my application randomly blocks, I found that
> it always has 2 threads running and I don't know what the second one is
> for.
> 
> It seems this thread is waiting on some condition lock :
> 
> #0  0xb7fe2424 in __kernel_vsyscall ()
> #1  0xb7428015 in pthread_cond_wait@@GLIBC_2.3.2 () at 
> ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
> #2  0xb76639dd in __pthread_cond_wait (cond=0x80de870, mutex=0x80de858) at 
> forward.c:139
> #3  0xb771d14f in ?? () from 
> /opt/GNUstep-trunk/Local/Library/Libraries/libobjc.so.4

Here, libobjc2 created this thread.  It exists to do cleanup on some data 
structures.  

> Once I saw my main thread blocked on the same condition/mutex (I think
> it was load_lock in NSBundle) : deadlock.

It shouldn't ever be blocking on that lock.  It's only ever used to pass off 
work to the background thread's queue.  If you're making a huge number of 
changes to runtime data structures then you might end up with this queue 
becoming full and the second thread having to do some work before the first is 
allowed to proceed, but it's quite unlikely.

It's not exposed outside of the runtime, so I'm a bit surprised if this is 
really the cause of your problem.  This thread is expected to spend almost all 
of its time asleep.  If you have libdispatch installed it won't exist at all.

> I'm wondering if my code is responsible by doing too much work in
> +initialize methods (ie creating singleton).

Nope, should be fine.

David

-- Sent from my Cray X1