[FFmpeg-devel] [PATCH] frame_thread_encoder: make task indexing deterministic.

[Ronald S. Bultje]

Hi,

On Sat, Apr 1, 2017 at 6:15 AM, Michael Niedermayer <michael at niedermayer.cc>
wrote:
[.]
>
> about the patch itself, the changes done to indexing seem not to
> change anything, it makes it possible for the variables to overflow
> though.
>

That's intentional, they're both unsigned and the one is guaranteed to be
larger than the other so the difference after subtract would still be
guaranteed to be <= n_threads. So although the indices overflow, the
subtraction will always be correct.


> IIUC the only change your patch does is to remove the outdata check
> from the quoted warning
>

Yes, because if you change the delay to be fixed (and equal to n_threads),
you no longer need the check. If the difference between indices is smaller
than n_threads, you don't return a packet. If it's equal, you do return a
packet.

its a while ago that i worked n this code but isnt this just "missing"
> a finished_task_mutex lock over the access ?


I don't know, it depends on what you're trying to accomplish. If you want a
fixed-frame delay, you don't need the access and so no mutex is needed. I
haven't thought much about what you need to get a variable-frame delay. To
me, a fixed-frame delay for intra-only codecs (which is what this API
currently accomplishes in practice) is exactly what you would expect,
variable-frame delay implies you're not actually using all threads. But
maybe I misunderstand.

Ronald