[vlc-devel] Deadlock on stop

[Romain Vimont | ®om]

Just to link it to the original discussion, I propose a patch here:
https://mailman.videolan.org/pipermail/vlc-devel/2014-May/098007.html

Le mercredi 30 avril 2014 à 17:11 +0200, Romain Vimont | ®om a écrit :
> Absolutely, so the problem is that the input thread does not finish.
> 
> After some investigations, I discovered that this is due to race
> conditions after calls to vlc_object_alive(). Moreover, this function
> has an explicit comment (src/misc/objects.c):
> 
>   /**
>    * This function returns true, except when it returns false.
>    * \warning Do not use this function. Ever. You were warned.
>    */
>   bool vlc_object_alive(vlc_object_t *obj)
> 
> The deadlock does not happen always at the same place, but always after
> a call to vlc_object_alive().
> 
> For instance, in AStreamPrebufferBlock() (src/input/stream.c), the call
> to AReadBlock() sometimes never ends, when vlc_object_alive() returns 1
> and the "stopping thread" is calling ObjectKillChildrens(), so there is
> no input data anymore (so AReadBlock() waits forever).
> 
> Although, this ObjectKillChildrens() have a reassuring comment too:
>   /* FIXME ObjectKillChildrens seems a very bad idea in fact */
> 
> Another example, the deadlock may occur during the call to
> p_demux->pf_demux(p_demux) after vlc_object_alive() in Open() of
> modules/demux/ts.c.
> 
> I think we need more than an atomic flag (currently "alive" in "struct
> vlc_object_internals"): we need to be able to interrupt AReadBlock() on
> stop (and other blocking functions which are currently called after a
> test to vlc_object_alive()).
> 
> What do you think?
> 
> Le vendredi 25 avril 2014 à 19:11 +0300, Rémi Denis-Courmont a écrit :
> > Le vendredi 25 avril 2014, 15:13:22 Romain Vimont | ®om a écrit :
> > > I guess there should be a call to vlc_sem_post() somewhere to wake it
> > > up… Maybe you have an idea?
> > 
> > It's in finish_joinable_thread().
> > 
> > -- 
> > Rémi Denis-Courmont
> > http://www.remlab.net/
> > 
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