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

[James Almer]

On 12/5/2017 1:40 PM, Mateusz 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;

No, the win32 wrapper should add volatile to the atomic_* typedefs if
anything. No other implementation needs it, so it must not be used here.

> 
> I will prepare a patch (but not before Friday -- lots of work).
> 
> Mateusz
> 
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>