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

[Hendrik Leppkes]

On Tue, Dec 5, 2017 at 8:23 PM, James Almer <jamrial at gmail.com> wrote:
> On 12/5/2017 8:12 AM, Hendrik Leppkes wrote:
>> On Tue, Dec 5, 2017 at 12:31 AM, Mateusz <mateuszb at poczta.onet.pl> 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.
>>
>> Yeah generally undefing all of them might result in errors in other
>> windows headers, so thats bad.
>>
>>>
>>> 2) #undef near
>>> after #include <windows.h> works in ffmpeg but is danger -- see 1)
>>
>> Doing it rather late,  ie. right before its used in the file should be
>> relatively safe. If not, we can always rename the variable.
>> But it seems to work so far. And from the nature of this bug, it
>> should just error out instead of resulting in other breakage - if it
>> happens.
>>
>>>
>>> 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
>>
>> We can't really revert those, so fixing them is better.
>>
>>> 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;
>>>      if (codec->caps_internal & FF_CODEC_CAP_INIT_THREADSAFE || !codec->init)
>>>          return 0;
>>>
>>>
>>
>> atomic_compare_exchange* usage is a bit iffy because it uses pointers,
>> and the compat wrappers don't fully represent all types properly (for
>> simplicity, implementing them in a generic way would be madness).
>> So this work-around seems fine to me, if it builds with GCC as well.
>
> GCC may accept it (No idea what code it would generate, though), but
> chances are Clang will complain since it's stricter about correct type
> usage in these functions, and making the variable to be passed as the
> "expected" parameter atomic is not correct.
>

Why does this code use atomics anyway?
The actual locking is done using a lock manager, and it warns/errors
when the lock functions are used concurrently without locking.

So, perhaps we should just remove that?

- Hendrik