[FFmpeg-devel] [PATCH] fix MSVC compilation errors

[Rostislav Pehlivanov]

On 5 December 2017 at 16:40, Mateusz <mateuszb at poczta.onet.pl> wrote:

> W dniu 05.12.2017 o 15:20, James Almer pisze:
> > On 12/4/2017 8:31 PM, Mateusz wrote:
> >> After some tests:
> >> 1) #undef far
> >> after #include <windows.h> is wrong -- in oleauto.h is declaration
> >> WINOLEAUTAPI VarUI1FromI8(LONG64 i64In, _Out_ BYTE FAR* pbOut);
> >> and 'FAR' is defined as 'far' which is define as empty.
> >>
> >> 2) #undef near
> >> after #include <windows.h> works in ffmpeg but is danger -- see 1)
> >>
> >> 3) after
> >> git revert 3701d499f8734ec5f3e7359de7311b15d92070b0
> >> git revert 590136e78da3d091ea99ab5432543d47a559a461
> >> and patch
> >> diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
> >> -    MXFPackage packages[2] = {};
> >> +    MXFPackage packages[2] = {{NULL}};
> >> VS 2017 can compile ffmpeg and fate stops at
> audiomatch-nero-16000-mono-he-m4a
> >> (without reverting 590136e hangs at api-flac-test.exe)
> >>
> >> 4) if for any reasons commits 3701d49 and 590136e shouldn't be reverted,
> >> we can apply this patch and
> >> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> >> index baf09119fe..b34a3803b8 100644
> >> --- a/libavcodec/utils.c
> >> +++ b/libavcodec/utils.c
> >> @@ -1943,7 +1943,7 @@ int av_lockmgr_register(int (*cb)(void **mutex,
> enum AVLockOp op))
> >>
> >>  int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
> >>  {
> >> -    _Bool exp = 0;
> >> +    atomic_bool exp = 0;
> >>      if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE ||
> !codec->init)
> >>          return 0;
> >>
> >> @@ -1969,7 +1969,7 @@ int ff_lock_avcodec(AVCodecContext *log_ctx,
> const AVCodec *codec)
> >>
> >>  int ff_unlock_avcodec(const AVCodec *codec)
> >>  {
> >> -    _Bool exp = 1;
> >> +    atomic_bool exp = 1;
> >
> > No, these are not meant to be atomic.
> >
> > _Bool is c99, so maybe we could replace its usage with int in these lock
> > functions. The result will be the exact same.
>
> In atomic types the main thing is width (sizeof).
> In atomic operations destination memory MUST BE sufficient
> to copy all bytes from source, in
> atomic_compare_exchange_strong(&ff_avcodec_locked, &exp, 1)
> sizeof(exp) MUST BE >= sizeof(ff_avcodec_locked) == sizeof(atomic_bool)
>
> In ffmpeg implementation of atomic code for MSVC sizeof(atomic_bool) == 8
> and sizeof(_Bool) < 8 -- it is the reason of hangs.
>
> And all volatile objects MUST BE explicitly volatile -- instead of
> static atomic_bool ff_avcodec_locked;
> should be
> static volatile atomic_bool ff_avcodec_locked;
>
> I will prepare a patch (but not before Friday -- lots of work).
>
> Mateusz
>
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>

That last thing belongs in the compat header rather than globablly in the
code.