Re: [PATCH 3/7] git-shared-util.h: add G*() versions of *ALLOC_*()

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Ævar

On 08/07/2022 15:20, Ævar Arnfjörð Bjarmason wrote:
> Add "gently" versions of ALLOC_ARRAY(), CALLOC_ARRAY() etc. using the
> naming convention G*() as a shorthand for "GENTLY_*()".

It might be nicer just to call them ALLOC_ARRAY_GENTLY() etc. As the 
return value needs to be checked it would make sense to implement them 
as expressions as I have done for XDL_ALLOC_ARRAY() etc.

> Nothing uses these functions yet, but as we'll see in subsequent
> commit(s) we're able to convert things that need e.g. non-fatal
> "ALLOC_GROW" behavior over to this.
> 
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>   git-shared-util.h | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/git-shared-util.h b/git-shared-util.h
> index 7b4479a0f72..718a8e00732 100644
> --- a/git-shared-util.h
> +++ b/git-shared-util.h
> @@ -8,8 +8,11 @@
>   #define FREE_AND_NULL(p) do { free(p); (p) = NULL; } while (0)
>   
>   #define ALLOC_ARRAY(x, alloc) (x) = xmalloc(st_mult(sizeof(*(x)), (alloc)))
> +#define GALLOC_ARRAY(x, alloc) (x) = malloc(st_mult(sizeof(*(x)), (alloc)))
>   #define CALLOC_ARRAY(x, alloc) (x) = xcalloc((alloc), sizeof(*(x)))
> +#define GCALLOC_ARRAY(x, alloc) (x) = calloc((alloc), sizeof(*(x)))
>   #define REALLOC_ARRAY(x, alloc) (x) = xrealloc((x), st_mult(sizeof(*(x)), (alloc)))
> +#define GREALLOC_ARRAY(x, alloc) (x) = realloc((x), st_mult(sizeof(*(x)), (alloc)))
>   
>   #define COPY_ARRAY(dst, src, n) copy_array((dst), (src), (n), sizeof(*(dst)) + \
>   	BUILD_ASSERT_OR_ZERO(sizeof(*(dst)) == sizeof(*(src))))
> @@ -71,17 +74,25 @@ static inline void move_array(void *dst, const void *src, size_t n, size_t size)
>    * added niceties.
>    *
>    * DO NOT USE any expression with side-effect for 'x', 'nr', or 'alloc'.
> + *
> + * GALLOC_GROW() behaves like ALLOC_GROW(), except that in malloc()
> + * failure we'll return NULL rather than dying.
>    */
> -#define ALLOC_GROW(x, nr, alloc) \
> +#define ALLOC_GROW_1(x, nr, alloc, gently) \
>   	do { \
>   		if ((nr) > alloc) { \
>   			if (alloc_nr(alloc) < (nr)) \
>   				alloc = (nr); \
>   			else \
>   				alloc = alloc_nr(alloc); \
> -			REALLOC_ARRAY(x, alloc); \

This leaks the old allocation if realloc() fails because it overwrites 
the original pointer with NULL, that is particularly bad as if realloc() 
fails we're already short of memory. XDL_ALLOC_GROW() shows how a 
possible way to do this.

Best Wishes

Phillip

> +			if (gently) \
> +				GREALLOC_ARRAY(x, alloc); \
> +			else \
> +				REALLOC_ARRAY(x, alloc); \
>   		} \
>   	} while (0)
> +#define ALLOC_GROW(x, nr, alloc) ALLOC_GROW_1(x, nr, alloc, 0)
> +#define GALLOC_GROW(x, nr, alloc) ALLOC_GROW_1(x, nr, alloc, 1)
>   
>   /*
>    * Similar to ALLOC_GROW but handles updating of the nr value and