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Re: [RFC PATCH 02/14] strvec: introduce `strvec_init_alloc()`

From
Junio C Hamano <gitster@pobox.com>
Date
Feb 26, 2026, 20:34 UTC
Message-ID
<xmqqh5r31byc.fsf@gitster.g>
In-Reply-To
<50efbbb0fe8d897d7c4cd51489af4cb4c4c49d02.1771978829.git.me@ttaylorr.com>
Taylor Blau <me@ttaylorr.com> writes:
Show 29 quoted lines
> When the caller knows upfront how many elements will be pushed onto a
> `strvec`, it is useful to pre-allocate enough space in the array to fit
> that many elements (and one additional slot to store NULL, indicating
> the end of the list.)
>
> Introduce `strvec_init_alloc()`, which allocates the backing array large
> enough to hold `alloc` elements and the termination marker without
> further reallocation.
>
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  strvec.c | 7 +++++++
>  strvec.h | 5 +++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/strvec.c b/strvec.c
> index f8de79f5579..f7f32a53b56 100644
> --- a/strvec.c
> +++ b/strvec.c
> @@ -10,6 +10,13 @@ void strvec_init(struct strvec *array)
>  	memcpy(array, &blank, sizeof(*array));
>  }
>  
> +void strvec_init_alloc(struct strvec *array, size_t alloc)
> +{
> +	CALLOC_ARRAY(array->v, st_add(alloc, 1));
> +	array->nr = 0;
> +	array->alloc = alloc + 1;
> +}

It is not satisifying that strvec_init() does *not* become a thin wrapper around this that says "my initial allocation is for zero elements", but that cannot be done easily as a strvec that begins as an empty one has a small optimization to avoid one-slot allocation only to store NULL. So, ... OK.

Previous: Taylor BlauNext: Junio C Hamano
Message 8 of 21 in “repack: incremental MIDX/bitmap-based repacking”
  1. 00/14 repack: incremental MIDX/bitmap-based repackingTaylor Blau, Feb 25, 2026
  2. 06/14 repack: track the ODB source via existing_packsTaylor Blau, Feb 25, 2026
  3. Taylor BlauFeb 25, 2026
  4. 01/14 midx: use `string_list` for retained MIDX filesTaylor Blau, Feb 25, 2026
  5. Junio C HamanoFeb 26, 2026
  6. Taylor BlauFeb 27, 2026
  7. 02/14 strvec: introduce `strvec_init_alloc()`Taylor Blau, Feb 25, 2026
  8. Junio C HamanoFeb 26, 2026
  9. Junio C HamanoFeb 26, 2026
  10. Taylor BlauFeb 27, 2026
  11. 03/14 midx: use `strvec` for `keep_hashes`Taylor Blau, Feb 25, 2026
  12. 04/14 midx: introduce `--checksum-only` for incremental MIDX writesTaylor Blau, Feb 25, 2026
  13. 05/14 midx: support custom `--base` for incremental MIDX writesTaylor Blau, Feb 25, 2026
  14. 07/14 midx: expose `midx_layer_contains_pack()`Taylor Blau, Feb 25, 2026
  15. 08/14 repack-midx: factor out `repack_prepare_midx_command()`Taylor Blau, Feb 25, 2026
  16. 09/14 repack-midx: extract `repack_fill_midx_stdin_packs()`Taylor Blau, Feb 25, 2026
  17. 10/14 repack-geometry: prepare for incremental MIDX repackingTaylor Blau, Feb 25, 2026
  18. 11/14 builtin/repack.c: convert `--write-midx` to an `OPT_CALLBACK`Taylor Blau, Feb 25, 2026
  19. 12/14 repack: implement incremental MIDX repackingTaylor Blau, Feb 25, 2026
  20. 13/14 repack: introduce `--write-midx=incremental`Taylor Blau, Feb 25, 2026
  21. 14/14 repack: allow `--write-midx=incremental` without `--geometric`Taylor Blau, Feb 25, 2026

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