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grep: make locking flag global

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The low-level grep code traditionally didn't care about
threading, as it doesn't do any threading itself and didn't
call out to other non-thread-safe code.  That changed with
0579f91 (grep: enable threading with -p and -W using lazy
attribute lookup, 2011-12-12), which pushed the lookup of
funcname attributes (which is not thread-safe) into the
low-level grep code.

As a result, the low-level code learned about a new global
"grep_attr_mutex" to serialize access to the attribute code.
A multi-threaded caller (e.g., builtin/grep.c) is expected
to initialize the mutex and set "use_threads" in the
grep_opt structure. The low-level code only uses the lock if
use_threads is set.

However, putting the use_threads flag into the grep_opt
struct is not the most logical place. Whether threading is
in use is not something that matters for each call to
grep_buffer, but is instead global to the whole program
(i.e., if any thread is doing multi-threaded grep, every
other thread, even if it thinks it is doing its own
single-threaded grep, would need to use the locking).  In
practice, this distinction isn't a problem for us, because
the only user of multi-threaded grep is "git-grep", which
does nothing except call grep.

This patch turns the opt->use_threads flag into a global
flag. More important than the nit-picking semantic argument
above is that this means that the locking functions don't
need to actually have access to a grep_opt to know whether
to lock. Which in turn can make adding new locks simpler, as
we don't need to pass around a grep_opt.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2012-02-02 03:18:29 -05:00 committed by Junio C Hamano
parent 828ea97de4
commit 78db6ea9dc
3 changed files with 13 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
builtin/grep.c
View File

@ -259,6 +259,7 @@ static void start_threads(struct grep_opt *opt)
pthread_cond_init(&cond_add, NULL);
pthread_cond_init(&cond_write, NULL);
pthread_cond_init(&cond_result, NULL);
grep_use_locks = 1;
for (i = 0; i < ARRAY_SIZE(todo); i++) {
strbuf_init(&todo[i].out, 0);
@ -307,6 +308,7 @@ static int wait_all(void)
pthread_cond_destroy(&cond_add);
pthread_cond_destroy(&cond_write);
pthread_cond_destroy(&cond_result);
grep_use_locks = 0;
return hit;
}
@ -1030,8 +1032,6 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
use_threads = 0;
#endif
opt.use_threads = use_threads;
#ifndef NO_PTHREADS
if (use_threads) {
if (opt.pre_context || opt.post_context || opt.file_break ||

18
grep.c
View File

@ -807,26 +807,28 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
}
#ifndef NO_PTHREADS
int grep_use_locks;
/*
* This lock protects access to the gitattributes machinery, which is
* not thread-safe.
*/
pthread_mutex_t grep_attr_mutex;
static inline void grep_attr_lock(struct grep_opt *opt)
static inline void grep_attr_lock(void)
{
if (opt->use_threads)
if (grep_use_locks)
pthread_mutex_lock(&grep_attr_mutex);
}
static inline void grep_attr_unlock(struct grep_opt *opt)
static inline void grep_attr_unlock(void)
{
if (opt->use_threads)
if (grep_use_locks)
pthread_mutex_unlock(&grep_attr_mutex);
}
#else
#define grep_attr_lock(opt)
#define grep_attr_unlock(opt)
#define grep_attr_lock()
#define grep_attr_unlock()
#endif
static int match_funcname(struct grep_opt *opt, const char *name, char *bol, char *eol)
@ -834,9 +836,9 @@ static int match_funcname(struct grep_opt *opt, const char *name, char *bol, cha
xdemitconf_t *xecfg = opt->priv;
if (xecfg && !xecfg->find_func) {
struct userdiff_driver *drv;
grep_attr_lock(opt);
grep_attr_lock();
drv = userdiff_find_by_path(name);
grep_attr_unlock(opt);
grep_attr_unlock();
if (drv && drv->funcname.pattern) {
const struct userdiff_funcname *pe = &drv->funcname;
xdiff_set_find_func(xecfg, pe->pattern, pe->cflags);

2
grep.h
View File

@ -116,7 +116,6 @@ struct grep_opt {
int show_hunk_mark;
int file_break;
int heading;
int use_threads;
void *priv;
void (*output)(struct grep_opt *opt, const void *data, size_t size);
@ -138,6 +137,7 @@ extern int grep_threads_ok(const struct grep_opt *opt);
* Mutex used around access to the attributes machinery if
* opt->use_threads. Must be initialized/destroyed by callers!
*/
extern int grep_use_locks;
extern pthread_mutex_t grep_attr_mutex;
#endif