app_bridgewait: Remove possibility of race condition between channels leaving/joining.

Bridges created by app_bridgewait previously had the "dissolve when empty" flag set.
This caused the bridge core to destroy them when the last channel had left. This
introduced a race condition where we may have a reference to the bridge but it is
not actually joinable when we try to join it. This flag has now been removed and the
bridge is guaranteed to be joinable at all times.

ASTERISK-23987 #close
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/3836/
........

Merged revisions 419538 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@419539 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_bridgewait.c

@@ -360,8 +360,7 @@ static struct wait_bridge_wrapper *get_wait_bridge_wrapper(const char *bridge_na
 	bridge = ast_bridge_base_new(AST_BRIDGE_CAPABILITY_HOLDING,
 		AST_BRIDGE_FLAG_MERGE_INHIBIT_TO | AST_BRIDGE_FLAG_MERGE_INHIBIT_FROM
 		| AST_BRIDGE_FLAG_SWAP_INHIBIT_TO | AST_BRIDGE_FLAG_SWAP_INHIBIT_FROM
-		| AST_BRIDGE_FLAG_TRANSFER_PROHIBITED | AST_BRIDGE_FLAG_DISSOLVE_EMPTY,
+		| AST_BRIDGE_FLAG_TRANSFER_PROHIBITED, APP_NAME, bridge_name, NULL);
-		APP_NAME, bridge_name, NULL);
 
 	if (!bridge) {
 		return NULL;
@@ -422,9 +421,10 @@ static int bridgewait_exec(struct ast_channel *chan, const char *data)
 	struct ast_bridge_features chan_features;
 	struct ast_flags flags = { 0 };
 	char *parse;
-	int bridge_join_failed = 0;
 	enum wait_bridge_roles role = ROLE_PARTICIPANT;
 	char *opts[OPT_ARG_ARRAY_SIZE] = { NULL, };
+	struct wait_bridge_wrapper *bridge_wrapper;
+	int res;
 
 	AST_DECLARE_APP_ARGS(args,
 		AST_APP_ARG(name);
@@ -469,36 +469,26 @@ static int bridgewait_exec(struct ast_channel *chan, const char *data)
 		return -1;
 	}
 
-	for (;;) {
+	bridge_wrapper = get_wait_bridge_wrapper(bridge_name);
-		RAII_VAR(struct wait_bridge_wrapper *, bridge_wrapper, get_wait_bridge_wrapper(bridge_name), wait_wrapper_removal);
-
 	if (!bridge_wrapper) {
 		ast_log(LOG_WARNING, "Failed to find or create waiting bridge '%s' for '%s'.\n", bridge_name, ast_channel_name(chan));
-			bridge_join_failed = 1;
+		ast_bridge_features_cleanup(&chan_features);
-			break;
+		return -1;
 	}
 
 	ast_verb(3, "%s is entering waiting bridge %s:%s\n", ast_channel_name(chan), bridge_name, bridge_wrapper->bridge->uniqueid);
-
+	res = ast_bridge_join(bridge_wrapper->bridge, chan, NULL, &chan_features, NULL, 0);
-		if (ast_bridge_join(bridge_wrapper->bridge, chan, NULL, &chan_features, NULL, 0)) {
+	wait_wrapper_removal(bridge_wrapper);
-			/* It's possible for a holding bridge to vanish out from under us since we can't lock it.
-			 * Unlink the wrapper and then loop if the bridge we try to enter is dissolved. */
-			ast_verb(3, "Waiting bridge '%s:%s' is no longer joinable. Creating new bridge and trying again.\n",
-				bridge_name, bridge_wrapper->bridge->uniqueid);
-			ao2_unlink(wait_bridge_wrappers, bridge_wrapper);
-			continue;
-		}
-
-		break;
-	}
-
 	ast_bridge_features_cleanup(&chan_features);
 
-	if (bridge_join_failed) {
+	if (res) {
-		return -1;
+		/* For the lifetime of the bridge wrapper the bridge itself will be valid, if an error occurs it is because
+		 * of extreme situations.
+		 */
+		ast_log(LOG_WARNING, "Failed to join waiting bridge '%s' for '%s'.\n", bridge_name, ast_channel_name(chan));
 	}
 
-	return ast_check_hangup_locked(chan) ? -1 : 0;
+	return (res || ast_check_hangup_locked(chan)) ? -1 : 0;
 }
 
 static int unload_module(void)