config: Speed up config template lookup

ast_category_get() has an (undocumented) implementation detail where it
tries to match the category name first by an explicit pointer comparison
and if that fails falls back to a normal match.

When initially building an ast_config during ast_config_load, this
pointer comparison can never succeed, but we will end up iterating all
categories twice. As the number of categories using a template
increases, this dual looping becomes quite expensive. So we pass a flag
to category_get_sep() indicating if a pointer match is even possible
before trying to do so, saving us a full pass over the list of current
categories.

In my tests, loading a file with 3 template categories and 12000
additional categories that use those 3 templates (this file configures
4000 PJSIP endpoints with AOR & Auth) takes 1.2 seconds. After this
change, that drops to 22ms.

Change-Id: I59b95f288e11eb6bb34f31ce4cc772136b275e4a

main/config.c

@@ -986,15 +986,17 @@ struct ast_category *ast_category_new_template(const char *name, const char *in_
 }
 
 static struct ast_category *category_get_sep(const struct ast_config *config,
-	const char *category_name, const char *filter, char sep)
+	const char *category_name, const char *filter, char sep, char pointer_match_possible)
 {
 	struct ast_category *cat;
 
+	if (pointer_match_possible) {
 		for (cat = config->root; cat; cat = cat->next) {
 			if (cat->name == category_name && does_category_match(cat, category_name, filter, sep)) {
 				return cat;
 			}
 		}
+	}
 
 	for (cat = config->root; cat; cat = cat->next) {
 		if (does_category_match(cat, category_name, filter, sep)) {
@@ -1008,7 +1010,7 @@ static struct ast_category *category_get_sep(const struct ast_config *config,
 struct ast_category *ast_category_get(const struct ast_config *config,
 	const char *category_name, const char *filter)
 {
-	return category_get_sep(config, category_name, filter, ',');
+	return category_get_sep(config, category_name, filter, ',', 1);
 }
 
 const char *ast_category_get_name(const struct ast_category *category)
@@ -1792,7 +1794,7 @@ static int process_text_line(struct ast_config *cfg, struct ast_category **cat,
 					if (cur[1] != ',') {
 						filter = &cur[1];
 					}
-					*cat = category_get_sep(cfg, catname, filter, '&');
+					*cat = category_get_sep(cfg, catname, filter, '&', 0);
 					if (!(*cat)) {
 						if (newcat) {
 							ast_category_destroy(newcat);
@@ -1810,7 +1812,7 @@ static int process_text_line(struct ast_config *cfg, struct ast_category **cat,
 				} else {
 					struct ast_category *base;
 
-					base = ast_category_get(cfg, cur, "TEMPLATES=include");
+					base = category_get_sep(cfg, cur, "TEMPLATES=include", ',', 0);
 					if (!base) {
 						if (newcat) {
 							ast_category_destroy(newcat);