[FFmpeg-devel] [PATCH] avutil/internal: Document ugly looking windows specific file related function renaming

[wm4]

On Wed, 1 Feb 2017 22:24:14 +0100
Michael Niedermayer <michaelni at gmx.at> wrote:

> On Wed, Feb 01, 2017 at 03:26:45PM +0100, wm4 wrote:
> > On Wed,  1 Feb 2017 14:35:50 +0100
> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> >   
> > > Found-by: ubitux
> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > > ---
> > >  libavutil/internal.h | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/libavutil/internal.h b/libavutil/internal.h
> > > index a19975d474..e97034887b 100644
> > > --- a/libavutil/internal.h
> > > +++ b/libavutil/internal.h
> > > @@ -243,8 +243,12 @@ void avpriv_request_sample(void *avc,
> > >  #pragma comment(linker, "/include:" EXTERN_PREFIX "avpriv_snprintf")
> > >  #endif
> > >  
> > > +// Rename shared function (both use and implementation of them) so they are not shared
> > > +// and each library carries its own copy of a implementation, this is needed as  
> > 
> > So why are they not appropriately named in the first place?
> >   
> > > +// the fd numbers are not transportable between libs on windows  
> > 
> > AFAIK they are, as long as they're linked to the same stdlib (which
> > probably is the case for libav*).  
> 
> here is the commit introducing the first function using this system.
> I belive its commit message is quite good and explains the reasoning.
> Beyond that iam the wrong one to discuss this with, iam not a windows
> developer and i didnt design this, which is not to say i like or
> dislike it. I just added one function IIRC and i wanted to document it
> as ubitux seemed to be confused for a moment when seeing it the first
> time
> 
> commit e743e7ae6ee7e535c4394bec6fe6650d2b0dbf65
> Author: Martin Storsjö <martin at martin.st>
> Date:   Fri Aug 9 11:06:46 2013 +0300
> 
>     libavutil: Make avpriv_open a library-internal function on msvcrt
> 
>     Add one copy of the function into each of the libraries, similarly
>     to what we do for log2_tab. When using static libs, only one
>     copy of the file_open.o object file gets included, while when
>     using shared libraries, each of them get a copy of its own.
> 
>     This fixes DLL builds with a statically linked C runtime, where
>     each DLL effectively has got its own instance of the C runtime,
>     where file descriptors can't be shared across runtimes.
> 
>     On systems not using msvcrt, the function is not duplicated.
> 
> [...]

Maybe this would be better:

// If each libav* DLL is statically linked to the C runtime, FDs can
// not be used across library boundaries. Duplicate these functions in
// each DLL to avoid this problem.