take down backend specific threads with backend

libs/ardour/ardour/graph.h

@@ -89,7 +89,7 @@ protected:
 	virtual void session_going_away ();
 
 private:
-	volatile bool        _quit_threads;
+	volatile bool        _threads_active;
 
 	void reset_thread_list ();
 	void drop_threads ();
@@ -136,6 +136,10 @@ private:
 	bool _process_noroll;
 	int  _process_retval;
 	bool _process_need_butler;
+
+	// enginer / thread connection
+	PBD::ScopedConnectionList engine_connections;
+	void engine_stopped ();
 };
 
 } // namespace

libs/ardour/graph.cc

@@ -53,7 +53,7 @@ int alloc_allowed ()
 
 Graph::Graph (Session & session)
         : SessionHandleRef (session)
-        , _quit_threads (false)
+        , _threads_active (false)
 	, _execution_sem ("graph_execution", 0)
 	, _callback_start_sem ("graph_start", 0)
 	, _callback_done_sem ("graph_done", 0)
@@ -71,9 +71,13 @@ Graph::Graph (Session & session)
         _current_chain = 0;
         _pending_chain = 0;
         _setup_chain   = 1;
-        _quit_threads = false;
         _graph_empty = true;
 
+
+	ARDOUR::AudioEngine::instance()->Running.connect_same_thread (engine_connections, boost::bind (&Graph::reset_thread_list, this));
+	ARDOUR::AudioEngine::instance()->Stopped.connect_same_thread (engine_connections, boost::bind (&Graph::engine_stopped, this));
+	ARDOUR::AudioEngine::instance()->Halted.connect_same_thread (engine_connections, boost::bind (&Graph::engine_stopped, this));
+
         reset_thread_list ();
 
 #ifdef DEBUG_RT_ALLOC
@@ -82,6 +86,14 @@ Graph::Graph (Session & session)
 #endif
 }
 
+void
+Graph::engine_stopped ()
+{
+	if (AudioEngine::instance()->process_thread_count() != 0) {
+		drop_threads ();
+	}
+}
+
 /** Set up threads for running the graph */
 void
 Graph::reset_thread_list ()
@@ -114,6 +126,7 @@ Graph::reset_thread_list ()
 			throw failed_constructor ();
 		}
         }
+        _threads_active = true;
 }
 
 void
@@ -132,7 +145,7 @@ Graph::session_going_away()
 void
 Graph::drop_threads ()
 {
-        _quit_threads = true;
+        _threads_active = false;
 
         uint32_t thread_count = AudioEngine::instance()->process_thread_count ();
 
@@ -145,8 +158,6 @@ Graph::drop_threads ()
 	AudioEngine::instance()->join_process_threads ();
 
 	_execution_tokens = 0;
-
-        _quit_threads = false;
 }
 
 void
@@ -243,7 +254,7 @@ Graph::restart_cycle()
         /* Block until the a process callback triggers us */
         _callback_start_sem.wait();
 
-        if (_quit_threads) {
+        if (!_threads_active) {
                 return;
         }
 
@@ -368,7 +379,7 @@ Graph::run_one()
                 pthread_mutex_unlock (&_trigger_mutex);
                 DEBUG_TRACE (DEBUG::ProcessThreads, string_compose ("%1 goes to sleep\n", pthread_name()));
                 _execution_sem.wait ();
-                if (_quit_threads) {
+                if (!_threads_active) {
                         return true;
                 }
                 DEBUG_TRACE (DEBUG::ProcessThreads, string_compose ("%1 is awake\n", pthread_name()));
@@ -421,13 +432,13 @@ Graph::main_thread()
 	
 	DEBUG_TRACE(DEBUG::ProcessThreads, "main thread is awake\n");
 
-        if (_quit_threads) {
+        if (!_threads_active) {
                 return;
         }
 
 	prep ();
 
-        if (_graph_empty && !_quit_threads) {
+        if (_graph_empty && _threads_active) {
                 _callback_done_sem.signal ();
                 DEBUG_TRACE(DEBUG::ProcessThreads, "main thread sees graph done, goes back to sleep\n");
                 goto again;
@@ -526,6 +537,8 @@ Graph::routes_no_roll (pframes_t nframes, framepos_t start_frame, framepos_t end
 {
 	DEBUG_TRACE (DEBUG::ProcessThreads, string_compose ("no-roll graph execution from %1 to %2 = %3\n", start_frame, end_frame, nframes));
 
+	if (!_threads_active) return 0;
+
         _process_nframes = nframes;
         _process_start_frame = start_frame;
         _process_end_frame = end_frame;