grep: move grep_source_init outside critical section

grep_source_init typically does three strdup()s, and in the threaded
case, the call from add_work() happens while holding grep_mutex.

We can thus reduce the time we hold grep_mutex by moving the
grep_source_init() call out of add_work(), and simply have add_work()
copy the initialized structure to the available slot in the todo
array.

This also simplifies the prototype of add_work(), since it no longer
needs to duplicate all the parameters of grep_source_init(). In the
callers of add_work(), we get to reduce the amount of code duplicated in
the threaded and non-threaded cases slightly (avoiding repeating the
long "GREP_SOURCE_OID, pathbuf.buf, path, oid" argument list); a
subsequent cleanup patch will make that even more so.

Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/grep.c

@@ -92,8 +92,7 @@ static pthread_cond_t cond_result;
 
 static int skip_first_line;
 
-static void add_work(struct grep_opt *opt, enum grep_source_type type,
-		     const char *name, const char *path, const void *id)
+static void add_work(struct grep_opt *opt, const struct grep_source *gs)
 {
 	grep_lock();
 
@@ -101,7 +100,7 @@ static void add_work(struct grep_opt *opt, enum grep_source_type type,
 		pthread_cond_wait(&cond_write, &grep_mutex);
 	}
 
-	grep_source_init(&todo[todo_end].source, type, name, path, id);
+	todo[todo_end].source = *gs;
 	if (opt->binary != GREP_BINARY_TEXT)
 		grep_source_load_driver(&todo[todo_end].source);
 	todo[todo_end].done = 0;
@@ -317,6 +316,7 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
 		     const char *path)
 {
 	struct strbuf pathbuf = STRBUF_INIT;
+	struct grep_source gs;
 
 	if (opt->relative && opt->prefix_length) {
 		quote_path_relative(filename + tree_name_len, opt->prefix, &pathbuf);
@@ -325,18 +325,22 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
 		strbuf_addstr(&pathbuf, filename);
 	}
 
+	grep_source_init(&gs, GREP_SOURCE_OID, pathbuf.buf, path, oid);
+
 #ifndef NO_PTHREADS
 	if (num_threads) {
-		add_work(opt, GREP_SOURCE_OID, pathbuf.buf, path, oid);
+		/*
+		 * add_work() copies gs and thus assumes ownership of
+		 * its fields, so do not call grep_source_clear()
+		 */
+		add_work(opt, &gs);
 		strbuf_release(&pathbuf);
 		return 0;
 	} else
 #endif
 	{
-		struct grep_source gs;
 		int hit;
 
-		grep_source_init(&gs, GREP_SOURCE_OID, pathbuf.buf, path, oid);
 		strbuf_release(&pathbuf);
 		hit = grep_source(opt, &gs);
 
@@ -348,24 +352,29 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
 static int grep_file(struct grep_opt *opt, const char *filename)
 {
 	struct strbuf buf = STRBUF_INIT;
+	struct grep_source gs;
 
 	if (opt->relative && opt->prefix_length)
 		quote_path_relative(filename, opt->prefix, &buf);
 	else
 		strbuf_addstr(&buf, filename);
 
+	grep_source_init(&gs, GREP_SOURCE_FILE, buf.buf, filename, filename);
+
 #ifndef NO_PTHREADS
 	if (num_threads) {
-		add_work(opt, GREP_SOURCE_FILE, buf.buf, filename, filename);
+		/*
+		 * add_work() copies gs and thus assumes ownership of
+		 * its fields, so do not call grep_source_clear()
+		 */
+		add_work(opt, &gs);
 		strbuf_release(&buf);
 		return 0;
 	} else
 #endif
 	{
-		struct grep_source gs;
 		int hit;
 
-		grep_source_init(&gs, GREP_SOURCE_FILE, buf.buf, filename, filename);
 		strbuf_release(&buf);
 		hit = grep_source(opt, &gs);