[vlc-devel] [PATCH] DXVA2: lock the buffer pool when getting/releasing a buffer (v4)

[Steve Lhomme]

On Wed, Apr 22, 2015 at 7:23 PM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> Le mercredi 22 avril 2015, 16:15:49 Steve Lhomme a écrit :
>> You can look at vaapi.c which uses similar "asymmetrical" calls. The
>> only difference is that he lock is always there, even if only 1 thread
>> will be used.
>
> Sigh. In principles, b_thread_safe_callbacks means that get_buffer2 (so Get())
> is thread-safe. Release() should always be thread-safe.
>
> In practice, b_thread_safe_callbacks is always true because HAVE_AVCODEC_MT is
> always defined, because FF_THREAD_FRAME is always defined.
>
> So the if-statement is useless and confusing at best.


OK, now I understand what you meant by "How so?
!avctx->thread_safe_callbacks only affects avctx->get_buffer2, so
va->get. I don't see how it helps va->release."

At some point I submited a patch where thread_safe_callbacks was set
to false on windows, rather than disabling frame multithreading in
avcodec. And it worked better. That's why I added the test so that the
lock is only used when actually necessary.

I don't think setting thread_safe_callbacks to false will be on the
table again, so I will submit a new patch where the lock is always
used, like in vaapi.c