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[PATCH 1/9] grep: make locking flag global

From
Jeff King <peff@peff.net>
Date
Feb 2, 2012, 08:18 UTC
Message-ID
<20120202081829.GA6786@sigill.intra.peff.net>
In-Reply-To
<20120202081747.GA10271@sigill.intra.peff.net>

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>
---
 builtin/grep.c |    4 ++--
 grep.c         |   18 ++++++++++--------
 grep.h         |    2 +-
 3 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/builtin/grep.c b/builtin/grep.c
index 5c2ae94..06983f9 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -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.name_only || opt.unmatch_name_only || opt.count)
diff --git a/grep.c b/grep.c
index 486230b..7a67c2f 100644
--- a/grep.c
+++ b/grep.c
@@ -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);
diff --git a/grep.h b/grep.h
index fb205f3..3653bb3 100644
--- a/grep.h
+++ b/grep.h
@@ -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
 

-- 
1.7.9.3.gc3fce1.dirty
Previous: Jeff KingNext: Jeff King
Message 25 of 43 in “git-grep while excluding files in a blacklist”
  1. Dov GrobgeldJan 17, 2012
  2. Nguyen Thai Ngoc DuyJan 17, 2012
  3. Junio C HamanoJan 17, 2012
  4. Nguyen Thai Ngoc DuyJan 18, 2012
  5. Don't search files with an unset "grep" attributeconrad.irwin@gmail.com, Jan 23, 2012
  6. Junio C HamanoJan 23, 2012
  7. Don't search files with an unset "grep" attributeConrad Irwin, Jan 23, 2012
  8. Junio C HamanoJan 24, 2012
  9. Jeff KingJan 25, 2012
  10. Stephen BashJan 26, 2012
  11. Jeff KingJan 26, 2012
  12. Michael HaggertyJan 26, 2012
  13. Jeff KingJan 27, 2012
  14. Junio C HamanoFeb 1, 2012
  15. Jeff KingFeb 1, 2012
  16. Jeff KingFeb 1, 2012
  17. Conrad IrwinFeb 1, 2012
  18. Jeff KingFeb 1, 2012
  19. Jeff KingFeb 1, 2012
  20. Junio C HamanoFeb 2, 2012
  21. 1/2 grep: let grep_buffer callers specify a binary flagJeff King, Feb 1, 2012
  22. Junio C HamanoFeb 2, 2012
  23. Jeff KingFeb 2, 2012
  24. 0/9 respect binary attribute in grepJeff King, Feb 2, 2012
  25. 1/9 grep: make locking flag globalJeff King, Feb 2, 2012
  26. 2/9 grep: move sha1-reading mutex into low-level codeJeff King, Feb 2, 2012
  27. 3/9 grep: refactor the concept of "grep source" into an objectJeff King, Feb 2, 2012
  28. 4/9 convert git-grep to use grep_source interfaceJeff King, Feb 2, 2012
  29. 5/9 grep: drop grep_buffer's "name" parameterJeff King, Feb 2, 2012
  30. 6/9 grep: cache userdiff_driver in grep_sourceJeff King, Feb 2, 2012
  31. Junio C HamanoFeb 2, 2012
  32. Jeff KingFeb 2, 2012
  33. 7/9 grep: respect diff attributes for binary-nessJeff King, Feb 2, 2012
  34. 8/9 grep: load file data after checking binary-nessJeff King, Feb 2, 2012
  35. 9/9 grep: pre-load userdiff drivers when threadedJeff King, Feb 2, 2012
  36. Jeff KingFeb 2, 2012
  37. Thomas RastFeb 2, 2012
  38. Jeff KingFeb 2, 2012
  39. Junio C HamanoFeb 2, 2012
  40. Pete WyckoffFeb 4, 2012
  41. Jeff KingFeb 4, 2012
  42. 2/2 grep: respect diff attributes for binary-nessJeff King, Feb 1, 2012
  43. Junio C HamanoFeb 1, 2012

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