[FFmpeg-devel] mutlithreading in ffmpeg?

[Reimar Döffinger]

On Tue, Mar 29, 2011 at 12:41:22PM -0700, Frank Barchard wrote:
> On Mon, Mar 28, 2011 at 10:50 PM, Reimar Döffinger <Reimar.Doeffinger at gmx.de
> > wrote:
> 
> > On 29 Mar 2011, at 03:32, Frank Barchard <fbarchard at google.com> wrote:
> > > On Sun, Mar 27, 2011 at 2:52 AM, Reimar Döffinger
> > > <Reimar.Doeffinger at gmx.de>wrote:
> > >
> > >> On Sat, Mar 26, 2011 at 12:14:40PM +0100, Michael Niedermayer wrote:
> > >>> This patch looks like it would break if libavcodec would be linked
> > >>> with an application that itself also used static pthreads
> > >>
> > >> Not to mention that it will crash if an application dynamically loads
> > >> libavcodec and then unloads it before exiting (i.e. the atexit code
> > >> will no longer exist when the program exits).
> > >>
> > > Thats what Chromium does - Each tab is a process that loads
> > avcodec-52.dll.
> > > Closing a tab unloads the dll.
> > > A DLL is really an .exe.  The atexit code runs when the DLL is unloaded.
> >
> > At least "man atexit" does not specify any such behaviour, are you really
> > sure you're not relying on an implementation detail?
> >
> 
> MSDN documents _onexit better:
> http://msdn.microsoft.com/en-us/library/zk17ww08(v=vs.71).aspx

Yes, that is better. However for a DLL the nicer way is to implement
DllInitialize and DllUnload functions.

> > Actually, are you really sure that you unload the avcodec dll separately
> > before exiting the tab process, that seems like a pointless thing to do.
> 
> Correct.  The process (for each tab) unloads the dll for us.  The chromium
> ffmpeg dll loader is here:
> http://src.chromium.org/viewvc/chrome/trunk/src/media/base/media_win.cc?content-type=text%2Fplain

Yes, that won't show the issue, it will only should when someone explicitly unloads
the DLL after having used it. It would then crash at exit, at least it should.
However considering:
http://permalink.gmane.org/gmane.comp.lang.c.pthreads.ms-windows/148
I have some doubts whether this is at all necessary.

> Ran another test - ff vp8
> >media_bench --flush --stream=video --video-threads=1 tulip2.webm
>         FPS:     378.99
> >media_bench --flush --stream=video --video-threads=2 tulip2.webm
>         FPS:     377.25
> just checking :)

Hm, wasn't it Theora you asked about at the start of the thread?
VP8 doesn't use threading so far, I think I'm not aware of anyone
working on it actually?