[vlc-devel] [PATCH] decoder: remove misleading comment

[Thomas Guillem]

On Tue, Sep 3, 2019, at 14:05, Steve Lhomme wrote:
> On 2019-09-03 13:43, Thomas Guillem wrote:
> > 
> > On Tue, Sep 3, 2019, at 13:22, Steve Lhomme wrote:
> >> The p_aout and p_vout need locking for reading as well (it wouldn't make much
> >> sense to only lock when writing).
> >>
> >> For example p_aout can be modified in the DecoderThread during a ReloadDecoder.
> > 
> > ReloadDecoder() will first unload the audio decoder before writing the aout so we are safe here. I could document it.
> 
> It reads p_owner->p_aout and do aout_DecDelete( p_aout ) on it in the 
> DecoderThread. It is the same kind of code done in the decoder thread 
> calling aout_update_format(). It is safe only because the 
> reading/resetting/setting is done under lock in both threads.

No, it is safe before the module is unloaded, so no threads can call aout_update_format().

> 
> IMO that contradicts the "These variables need locking on write(only)" doc.
> 
> >>
> >> p_vout cannot be modified outside of the vout_update_format/spu_new_buffer but
> >> it is also access in the DecoderThread, for example during DecoderProcessFlush()
> >> or the OutputChangeXXX functions.
> > 
> > That is what my comment say no ?
> 
> Yes
> 
> >>
> >> For functions only called by the decoder, it might be OK not to lock as the
> >> p_out/p_aout should only change during vout_update_format/aout_update_format
> >> which the decoder should call before doing other calls from various threads.
> >> ---
> >>   src/input/decoder.c | 3 +--
> >>   1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/src/input/decoder.c b/src/input/decoder.c
> >> index 65e3dd6f6c..7011c99226 100644
> >> --- a/src/input/decoder.c
> >> +++ b/src/input/decoder.c
> >> @@ -101,12 +101,11 @@ struct decoder_owner
> >>       vlc_cond_t  wait_acknowledge;
> >>       vlc_cond_t  wait_fifo; /* TODO: merge with wait_acknowledge */
> >>   
> >> -    /* -- These variables need locking on write(only) -- */
> >> +    /* -- Theses variables need locking on read *and* write -- */
> >>       audio_output_t *p_aout;
> >>   
> >>       vout_thread_t   *p_vout;
> >>   
> >> -    /* -- Theses variables need locking on read *and* write -- */
> >>       /* Preroll */
> >>       vlc_tick_t i_preroll_end;
> >>   
> >> -- 
> >> 2.17.1
> >>
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