[FFmpeg-devel] [PATCH] Use ff_thread_once() to initialize sin/cos static tables.

Michael Niedermayer michael at niedermayer.cc
Sun Oct 25 12:56:22 CET 2015

On Sun, Oct 25, 2015 at 11:48:12AM +0000, Derek Buitenhuis wrote:
> On 10/25/2015 11:44 AM, Michael Niedermayer wrote:
> >> One could argue this is not a representative sample. It's a single small file,
> >> which must always init (as opposed to a longer running process such as Chrome.
> >> Whereas if you have a longer sample, it wouldn't even be within the margin of
> >> error, I bet.
> > 
> > If the usecase is to probe many files, then file duration would not
> > help hideing the init time. (to fill a GUI list or whatever)
> I reject this notion. You are completely discounting that people use
> libavcodec *as a library*, and not via CLI.
> > Also startup time for normal playback itself does matter, as its
> > part of user vissible responsiveness, the user clicks play in his
> > players playlist and if that isnt instantaneaously starting playback
> > the user notices. So IMO startup time is not irrelevant
> I agree, but neither is thread-safety. Perhaps there is a middle ground.

the problem that causes the slowdown should be due to initializing all
table sizes when only 1 or a few small ones are needed
making the init more fine grained (as it was) should solve this
that could be done with a single mutex (not of once type) and
initializing only the needed table when its not already inited
or with a once mutex for each table size
there are certainly also other options

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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