At 04:17 PM 1/27/2008, Benny Prijono wrote:
>On 1/25/08, Michael Broughton <Michael_Broughton at advanis.ca> wrote:
> > Hello,
> >
> > I am looking at two functions in stream.c: pjmedia_stream_destroy and
> > on_rx_rtp. I am trying to figure out if the following scenario is possible:
> >
> > 1. Thread A calls pjmedia_stream_destroy, which locks stream->jb_mutex.
> >
> > 2. Thread B calls on_rx_rtp, which tries to lock stream->jb_mutex but
> > cannot right away because thread A already holds the lock.
> >
> > 3. Thread A goes about it's work and then free's stream->jb_mutex.
> >
> > 4. Thread B, still trying to lock stream->jb_mutex, segfaults because
> > thread A deallocated stream->jb_mutex and zeroed out the pointer.
> >
> >
> > I have been trying to follow the code and it almost looks like this is
> > possible. Can anyone confirm or disprove this?
> >
>
>Hi Michael,
>
>I've got to say that the scenario looks valid, rather unfortunately. I
>haven't had idea on how to solve it though.
Ok got an idea here. It has to do with lock_count which associated
with the lock.
enter_lock():
increments lock count
tries to get the OS lock.
leave_lock():
decrements lock count
releases the OS lock.
if lock_count==0 and marked for deletion // was intended to be
deleted elsewhere do it now.
delete lock.
destory_lock():
if lock_count==0 // we can delete now
remove lock from memory
set pointer to zero.
else
mark lock for deletion. // we can delete somewhere else.
>cheers,
> -benny
>
>
>
> > Thanks,
> >
> > --
> > Michael Broughton, Advanis
> >
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