Re: [RFC PATCH v4 2/3] grep: make PCRE2 aware of custom allocator

[Junio C Hamano <gitster@pobox.com>]

Carlo Marcelo Arenas Belón  <carenas@gmail.com> writes:

As we already have such an ifdef block here...

> +#ifdef USE_LIBPCRE2
> +static pcre2_general_context *pcre2_global_context;
> +
> +#ifdef USE_NED_ALLOCATOR
> +static void *pcre2_malloc(PCRE2_SIZE size, MAYBE_UNUSED void *memory_data)
> +{
> +	return xmalloc(size); /* will use nedalloc underneath */
> +}
> +
> +static void pcre2_free(void *pointer, MAYBE_UNUSED void *memory_data)
> +{
> +	return free(pointer);
> +}
> +#endif
> +#endif

... perhaps an ugly ifdef block like this one ...

> +static struct grep_pat *create_grep_pat(struct grep_opt *opt,
> +					const char *pat, size_t patlen,
>  					const char *origin, int no,
>  					enum grep_pat_token t,
>  					enum grep_header_field field)
>  {
>  	struct grep_pat *p = xcalloc(1, sizeof(*p));
> +
> +#if defined(USE_LIBPCRE2) && defined(USE_NED_ALLOCATOR)
> +	/* BUG: this is technically not needed if we will do UTF matching
> +	 *      but UTF locale detection is currently broken  */
> +	/* SMELL: opt shouldn't be needed at this level but it is used
> +	 *        here to keep the way we were detecting the need for
> +	 *        the chartable consistent and until it can be refactored
> +	 *        properly.  the NULL check is needed as a workaround
> +	 *        for segfaulting in t7810.102 and should also go */
> +	/* TODO: has_non_ascii doesn't support NUL in pattern */
> +	if (!pcre2_global_context && opt && opt->ignore_case &&
> +		has_non_ascii(pat))
> +		pcre2_global_context = pcre2_general_context_create(
> +					pcre2_malloc, pcre2_free, NULL);
> +#endif
> +

... can be abstracted away by *not* having the #if/#endif here and
instead have a line that looks like this:

	setup_pcre2_as_needed(opt, pat);

which implementation can be prepared near the top, close to where
pcre2_malloc/free are defined (or not) above, i.e.

	#if defined(USE_LIBPCRE2) && defined(USE_NED_ALLOCATOR)
	static void setup_pcre2_as_needed(struct grep_opt *opt,	const char *pat)
	{
		... the above one ...
	}
	#else
	#define setup_pcre2_as_needed(ignore1, ignore2) /* nothing */
	#endif

The conditional code in grep_destroy() can be eliminated in a
similar fashion, i.e.

	void grep_destroy(void)
	{
		cleanup_pcre2_as_needed();
	}

with

	#ifdef USE_LIBPCRE2
	static void cleanup_pcre2_as_needed(void)
	{
		pcre2_general_context_free(pcre2_global_context);
	}
	#else
	#define cleanup_pcre2_as_needed() /* nothing */
	#endif

near the top (the beneral idea is to "call" a helper function whose
name describes what the call is for in a more general terms, and let
only the implementation details be hidden inside ifdef blocks).

Also, 

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