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

[Mateusz]

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