[FFmpeg-devel] [PATCH 3/8] avutil/mem: Add av_fast_realloc_array()

[Andreas Rheinhardt]

Tomas Härdin:
> tis 2022-09-27 klockan 17:23 +0200 skrev Tomas Härdin:
>> mån 2022-09-26 klockan 16:24 +0200 skrev Tomas Härdin:
>>> mån 2022-09-26 klockan 14:25 +0200 skrev Andreas Rheinhardt:
>>>> Anton Khirnov:
>>>>> Quoting Andreas Rheinhardt (2022-07-14 14:51:07)
>>>>>> Anton Khirnov:
>>>>>>> Quoting Andreas Rheinhardt (2022-07-12 16:12:16)
>>>>>>>> Anton really dislikes the av_fast_* naming and instead
>>>>>>>> wants
>>>>>>>> this to be
>>>>>>>> called av_realloc_array_reuse(). I don't care either way.
>>>>>>>> Any
>>>>>>>> more
>>>>>>>> opinions on this (or on the patch itself)?
>>>>>>>
>>>>>>> If people dislike _reuse(), I am open to other reasonable
>>>>>>> suggestions.
>>>>>>> This 'fast' naming sucks because
>>>>>>> - it tells you nothing about how this function is "fast"
>>>>>>> - it is added at the beginning rather than the end, which
>>>>>>> is
>>>>>>>   against standard namespacing conventions
>>>>>>>
>>>>>>
>>>>>> Isn't reusing the basic modus operandi for a reallocation
>>>>>> function? So
>>>>>> your suggested name doesn't seem to fit either.
>>>>>
>>>>> Ordinary realloc just keeps the data, I wouldn't call that
>>>>> "reuse"
>>>>> since
>>>>> it will often be a copy. This "fast" realloc OTOH reuses the
>>>>> actual
>>>>> buffer, same as all the other "fast" mem.h functions.
>>>>>
>>>>> But feel free to suggest another naming pattern if you can
>>>>> think
>>>>> of
>>>>> one.
>>>>>
>>>>
>>>> I see two differences between this function and ordinary realloc:
>>>> It
>>>> never shrinks the buffer and it overallocates. These two
>>>> properties
>>>> make
>>>> it more likely that these functions can avoid copies more often
>>>> than
>>>> plain realloc (but in contrast to realloc, we can not grow the
>>>> buffer
>>>> in
>>>> case there is free space after it), but it is nevertheless the
>>>> same
>>>> as
>>>> realloc.
>>>>
>>>> But I don't really care that much about the name and will
>>>> therefore
>>>> use
>>>> your name as I can't come up with anything better.
>>>> (Of course, I am still open to alternative suggestions.)
>>>>
>>>> - Andreas
>>>
>>> So this means av_realloc_array_reuse()? Eh, it works. I will add a
>>> function that also zeroes the newly allocated space, what should we
>>> call that? av_realloc_array_reusez()?
>>> av_realloc_array_reuse_zerofill()?
>>
>> Here's a draft patch that calls it av_reallocz_array_reuse(). Needs a
>> minor version bump of course
> 
> This makes me realize something: av_realloc_array_reuse() requires that
> *nb_allocated == 0 initially but this isn't specified in the
> documentation. Patch attached relaxes this.
> 

* @param[in,out] nb_allocated  Pointer to the number of elements of the
array
*                              `*ptr`. `*nb_allocated` is updated to the new
*                              number of allocated elements.

If *ptr == NULL, then the number of elements of said array is (of
course) zero, so *nb_allocated has to be set to that. (But if you think
that this needs to be said explicitly, I can document it.)

- Andreas