stream: Make the topology a reference counted object.

The stream topology has no lock of its own resulting in
another lock protecting it in some way (for example the
channel lock). If multiple channels are being juggled at
the same time this can be problematic. This change makes
the topology a reference counted object instead which
guarantees it will remain valid even without the channel
lock being held.

Change-Id: I4f4d3dd856a033ed55fe218c3a4fab364afedb03

bridges/bridge_softmix.c

@@ -2159,15 +2159,7 @@ static void softmix_bridge_stream_topology_changed(struct ast_bridge *bridge, st
 		ast_bridge_channel_lock(participant);
 		ast_channel_lock(participant->chan);
 
-		topology = ast_channel_get_stream_topology(participant->chan);
+		topology = ao2_bump(ast_channel_get_stream_topology(participant->chan));
-		if (topology) {
-			/*
-			 * Sigh.  We have to clone to avoid deadlock in
-			 * map_source_to_destinations() because topology
-			 * is not an ao2 object.
-			 */
-			topology = ast_stream_topology_clone(topology);
-		}
 		if (!topology) {
 			/* Oh, my, we are in trouble. */
 			ast_channel_unlock(participant->chan);

include/asterisk/stream.h

@@ -306,6 +306,8 @@ void ast_stream_set_rtp_codecs(struct ast_stream *stream, struct ast_rtp_codecs
  * \retval NULL failure
  *
  * \since 15
+ *
+ * \note This returns an ao2 refcounted object
  */
 struct ast_stream_topology *ast_stream_topology_alloc(void);
 
@@ -318,6 +320,8 @@ struct ast_stream_topology *ast_stream_topology_alloc(void);
  * \retval NULL failure
  *
  * \since 15
+ *
+ * \note This returns an ao2 refcounted object
  */
 struct ast_stream_topology *ast_stream_topology_clone(
 	const struct ast_stream_topology *topology);
@@ -337,7 +341,7 @@ int ast_stream_topology_equal(const struct ast_stream_topology *left,
 	const struct ast_stream_topology *right);
 
 /*!
- * \brief Destroy a stream topology
+ * \brief Unreference and destroy a stream topology
  *
  * \param topology The topology of streams
  *

main/stream.c

@@ -344,18 +344,26 @@ void ast_stream_set_rtp_codecs(struct ast_stream *stream, struct ast_rtp_codecs
 	stream->rtp_codecs = rtp_codecs;
 }
 
+static void stream_topology_destroy(void *data)
+{
+	struct ast_stream_topology *topology = data;
+
+	AST_VECTOR_CALLBACK_VOID(&topology->streams, ast_stream_free);
+	AST_VECTOR_FREE(&topology->streams);
+}
+
 #define TOPOLOGY_INITIAL_STREAM_COUNT 2
 struct ast_stream_topology *ast_stream_topology_alloc(void)
 {
 	struct ast_stream_topology *topology;
 
-	topology = ast_calloc(1, sizeof(*topology));
+	topology = ao2_alloc_options(sizeof(*topology), stream_topology_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
 	if (!topology) {
 		return NULL;
 	}
 
 	if (AST_VECTOR_INIT(&topology->streams, TOPOLOGY_INITIAL_STREAM_COUNT)) {
-		ast_free(topology);
+		ao2_ref(topology, -1);
 		topology = NULL;
 	}
 
@@ -440,13 +448,7 @@ int ast_stream_topology_equal(const struct ast_stream_topology *left,
 
 void ast_stream_topology_free(struct ast_stream_topology *topology)
 {
-	if (!topology) {
+	ao2_cleanup(topology);
-		return;
-	}
-
-	AST_VECTOR_CALLBACK_VOID(&topology->streams, ast_stream_free);
-	AST_VECTOR_FREE(&topology->streams);
-	ast_free(topology);
 }
 
 int ast_stream_topology_append_stream(struct ast_stream_topology *topology, struct ast_stream *stream)