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grep/pcre2: move back to thread-only PCREv2 structures 

Change the setup of the "pcre2_general_context" to happen per-thread
in compile_pcre2_pattern() instead of in grep_init().

This change brings it in line with how the rest of the pcre2_* members
in the grep_pat structure are set up.

As noted in the preceding commit the approach 513f2b0bbd (grep: make
PCRE2 aware of custom allocator, 2019-10-16) took to allocate the
pcre2_general_context seems to have been initially based on a
misunderstanding of how PCREv2 memory allocation works.

The approach of creating a global context in grep_init() is just added
complexity for almost zero gain. On my system it's 24 bytes saved
per-thread. For comparison PCREv2 will then go on to allocate at least
a kilobyte for its own thread-local state.

As noted in 6d423dd542 (grep: don't redundantly compile throwaway
patterns under threading, 2017-05-25) the grep code is intentionally
not trying to micro-optimize allocations by e.g. sharing some PCREv2
structures globally, while making others thread-local.

So let's remove this special case and make all of them thread-local
again for simplicity. With this change we could move the
pcre2_{malloc,free} functions around to live closer to their current
use. I'm not doing that here to keep this change small, that cleanup
will be done in a follow-up commit.

See also the discussion in 94da9193a6 (grep: add support for PCRE v2,
2017-06-01) about thread safety, and Johannes's comments[1] to the
effect that we should be doing what this patch is doing.

1. https://lore.kernel.org/git/nycvar.QRO.7.76.6.1908052120302.46@tvgsbejvaqbjf.bet/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Ævar Arnfjörð Bjarmason 2021-02-18 01:07:27 +01:00 committed by Junio C Hamano
parent 8d12851342
commit cbe81e653f
3 changed files with 17 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
builtin/grep.c
View File

@ -1175,6 +1175,5 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
run_pager(&opt, prefix);
clear_pathspec(&pathspec);
free_grep_patterns(&opt);
grep_destroy();
return !hit;
}

41
grep.c
View File

@ -41,7 +41,6 @@ static struct grep_opt grep_defaults = {
};
#ifdef USE_LIBPCRE2
static pcre2_general_context *pcre2_global_context;
#define GREP_PCRE2_DEBUG_MALLOC 0
static void *pcre2_malloc(PCRE2_SIZE size, MAYBE_UNUSED void *memory_data)
@ -163,20 +162,9 @@ int grep_config(const char *var, const char *value, void *cb)
* Initialize one instance of grep_opt and copy the
* default values from the template we read the configuration
* information in an earlier call to git_config(grep_config).
*
* If using PCRE, make sure that the library is configured
* to use the same allocator as Git (e.g. nedmalloc on Windows).
*
* Any allocated memory needs to be released in grep_destroy().
*/
void grep_init(struct grep_opt *opt, struct repository *repo, const char *prefix)
{
#if defined(USE_LIBPCRE2)
if (!pcre2_global_context)
pcre2_global_context = pcre2_general_context_create(
pcre2_malloc, pcre2_free, NULL);
#endif
*opt = grep_defaults;
opt->repo = repo;
@ -186,13 +174,6 @@ void grep_init(struct grep_opt *opt, struct repository *repo, const char *prefix
opt->header_tail = &opt->header_list;
}
void grep_destroy(void)
{
#ifdef USE_LIBPCRE2
pcre2_general_context_free(pcre2_global_context);
#endif
}
static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, struct grep_opt *opt)
{
/*
@ -384,13 +365,20 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
int patinforet;
size_t jitsizearg;
/* pcre2_global_context is initialized in grep_init */
/*
* Call pcre2_general_context_create() before calling any
* other pcre2_*(). It sets up our malloc()/free() functions
* with which everything else is allocated.
*/
p->pcre2_general_context = pcre2_general_context_create(
pcre2_malloc, pcre2_free, NULL);
if (!p->pcre2_general_context)
die("Couldn't allocate PCRE2 general context");
if (opt->ignore_case) {
if (!opt->ignore_locale && has_non_ascii(p->pattern)) {
if (!pcre2_global_context)
BUG("pcre2_global_context uninitialized");
p->pcre2_tables = pcre2_maketables(pcre2_global_context);
p->pcre2_compile_context = pcre2_compile_context_create(pcre2_global_context);
p->pcre2_tables = pcre2_maketables(p->pcre2_general_context);
p->pcre2_compile_context = pcre2_compile_context_create(p->pcre2_general_context);
pcre2_set_character_tables(p->pcre2_compile_context,
p->pcre2_tables);
}
@ -411,7 +399,7 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
p->pcre2_compile_context);
if (p->pcre2_pattern) {
p->pcre2_match_data = pcre2_match_data_create_from_pattern(p->pcre2_pattern, pcre2_global_context);
p->pcre2_match_data = pcre2_match_data_create_from_pattern(p->pcre2_pattern, p->pcre2_general_context);
if (!p->pcre2_match_data)
die("Couldn't allocate PCRE2 match data");
} else {
@ -491,10 +479,11 @@ static void free_pcre2_pattern(struct grep_pat *p)
pcre2_code_free(p->pcre2_pattern);
pcre2_match_data_free(p->pcre2_match_data);
#ifdef GIT_PCRE2_VERSION_10_34_OR_HIGHER
pcre2_maketables_free(pcre2_global_context, p->pcre2_tables);
pcre2_maketables_free(p->pcre2_general_context, p->pcre2_tables);
#else
free((void *)p->pcre2_tables);
#endif
pcre2_general_context_free(p->pcre2_general_context);
}
#else /* !USE_LIBPCRE2 */
static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)

3
grep.h
View File

@ -14,6 +14,7 @@
typedef int pcre2_code;
typedef int pcre2_match_data;
typedef int pcre2_compile_context;
typedef int pcre2_general_context;
#endif
#ifndef PCRE2_MATCH_INVALID_UTF
/* PCRE2_MATCH_* dummy also with !USE_LIBPCRE2, for test-pcre2-config.c */
@ -75,6 +76,7 @@ struct grep_pat {
pcre2_code *pcre2_pattern;
pcre2_match_data *pcre2_match_data;
pcre2_compile_context *pcre2_compile_context;
pcre2_general_context *pcre2_general_context;
const uint8_t *pcre2_tables;
uint32_t pcre2_jit_on;
unsigned fixed:1;
@ -167,7 +169,6 @@ struct grep_opt {
int grep_config(const char *var, const char *value, void *);
void grep_init(struct grep_opt *, struct repository *repo, const char *prefix);
void grep_destroy(void);
void grep_commit_pattern_type(enum grep_pattern_type, struct grep_opt *opt);
void append_grep_pat(struct grep_opt *opt, const char *pat, size_t patlen, const char *origin, int no, enum grep_pat_token t);