Re: [FFmpeg-devel] [PATCH v4 3/5] avutil: add obj-c helpers into header-only include

[Ridley Combs <rcombs@rcombs.me>]

> On Dec 19, 2021, at 12:03, Marvin Scholz <epirat07@gmail.com> wrote:
> 
> 
> 
> On 19 Dec 2021, at 18:35, Aman Karmani wrote:
> 
>> On Sun, Dec 19, 2021 at 9:09 AM James Almer <jamrial@gmail.com> wrote:
>> 
>>> On 12/17/2021 5:04 PM, Aman Karmani wrote:
>>>> From: Aman Karmani <aman@tmm1.net>
>>>> 
>>>> Reviewed-by: Ridley Combs <rcombs@rcombs.me>
>>>> Signed-off-by: Aman Karmani <aman@tmm1.net>
>>>> ---
>>>>  libavutil/objc.h | 32 ++++++++++++++++++++++++++++++++
>>>>  1 file changed, 32 insertions(+)
>>>>  create mode 100644 libavutil/objc.h
>>>> 
>>>> diff --git a/libavutil/objc.h b/libavutil/objc.h
>>>> new file mode 100644
>>>> index 0000000000..0db993f716
>>>> --- /dev/null
>>>> +++ b/libavutil/objc.h
>>>> @@ -0,0 +1,32 @@
>>>> +/*
>>>> + * This file is part of FFmpeg.
>>>> + *
>>>> + * FFmpeg is free software; you can redistribute it and/or
>>>> + * modify it under the terms of the GNU Lesser General Public
>>>> + * License as published by the Free Software Foundation; either
>>>> + * version 2.1 of the License, or (at your option) any later version.
>>>> + *
>>>> + * FFmpeg is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>>> + * Lesser General Public License for more details.
>>>> + *
>>>> + * You should have received a copy of the GNU Lesser General Public
>>>> + * License along with FFmpeg; if not, write to the Free Software
>>>> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>>> 02110-1301 USA
>>>> + */
>>>> +
>>>> +#ifndef AVUTIL_OBJC_H
>>>> +#define AVUTIL_OBJC_H
>>>> +
>>>> +#include <Foundation/Foundation.h>
>>>> +
>>>> +static inline void ff_objc_release(NSObject **obj)
>>>> +{
>>>> +    if (*obj) {
>>>> +        [*obj release];
>>>> +        *obj = nil;
>>>> +    }
>>>> +}
>>>> +
>>>> +#endif /* AVUTIL_OBJC_H */
>>> 
>>> This breaks checkheaders. It should be added to SKIPHEADERS with the
>>> corresponding check.
>>> 
>> 
>> Sorry, will fix.
>> 
>> 
>>> 
>>> Also, why is this in lavu if it's ultimately only used in lavfi? And
>>> does it need to be a separate header at all? It's apparently not even C.
>>> 
>> 
>> It is a generic helper requested by rcombs. I think the plan is to reuse it
>> in other filters/decoders/encoders written in obj-c.
>> 
>> One of the reasons is becausing calling `[nil release]` can crash.
> 
> That's not true, dispatching a message to nil in Objective-C has no effect.
> I don't really see the benefit of this helper, personally.

The main point is the same as av_freep: it combines releasing the memory and nulling out the pointer into a single call, so we can't end up with dangling pointers by mistake.

> 
>> 
>> You're right that it is not C, its obj-c and that's why it was simpler to
>> have it be an include only header. I'm not sure if using a different
>> extension would have been preferred.
>> 
>> Aman
>> 
>> 
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