invalidate_ref_cache(): take the submodule as parameter

Instead of invalidating the ref cache on an all-or-nothing basis,
invalidate the cache for a specific submodule.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -202,13 +202,9 @@ static struct ref_cache *get_ref_cache(const char *submodule)
 	return refs;
 }
 
-static void invalidate_ref_cache(void)
+static void invalidate_ref_cache(const char *submodule)
 {
-	struct ref_cache *refs = ref_cache;
-	while (refs) {
-		clear_ref_cache(refs);
-		refs = refs->next;
-	}
+	clear_ref_cache(get_ref_cache(submodule));
 }
 
 static void read_packed_refs(FILE *f, struct ref_array *array)
@@ -1228,7 +1224,7 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
 	ret |= repack_without_ref(refname);
 
 	unlink_or_warn(git_path("logs/%s", lock->ref_name));
-	invalidate_ref_cache();
+	invalidate_ref_cache(NULL);
 	unlock_ref(lock);
 	return ret;
 }
@@ -1527,7 +1523,7 @@ int write_ref_sha1(struct ref_lock *lock,
 		unlock_ref(lock);
 		return -1;
 	}
-	invalidate_ref_cache();
+	invalidate_ref_cache(NULL);
 	if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
 	    (strcmp(lock->ref_name, lock->orig_ref_name) &&
 	     log_ref_write(lock->orig_ref_name, lock->old_sha1, sha1, logmsg) < 0)) {