redesign cross-thread registration/signalling system

This new design will work even when threads that need to receive
messages from RT threads are created *after* the RT threads. The
existing design would fail because the RT thread(s) would never
be known the later created threads, and so signals emitted by the
RT thread and causing call_slot() in the receiver would end up
being enqueued using a lock-protected list. The new design ensures
that communication always uses a lock-free FIFO instead

1 files changed, 17 insertions, 2 deletions

diff --git a/libs/ardour/globals.cc b/libs/ardour/globals.cc
index b2ad67d053..9f4a1399b3 100644
--- a/libs/ardour/globals.cc
+++ b/libs/ardour/globals.cc
@@ -97,6 +97,7 @@
 #include "ardour/event_type_map.h"
 #include "ardour/filesystem_paths.h"
 #include "ardour/midi_region.h"
+#include "ardour/midi_ui.h"
 #include "ardour/midiport_manager.h"
 #include "ardour/mix.h"
 #include "ardour/operations.h"
@@ -513,6 +514,22 @@ ARDOUR::init (bool use_windows_vst, bool try_optimization, const char* localedir
 #endif
 	(void) EventTypeMap::instance();
 
+	ControlProtocolManager::instance().discover_control_protocols ();
+
+	/* for each control protocol, check for a request buffer factory method
+	   and if it exists, store it in the EventLoop list of such
+	   methods. This allows the relevant threads to register themselves
+	   with EventLoops so that signal emission can be RT-safe.
+	*/
+
+	ControlProtocolManager::instance().register_request_buffer_factories ();
+	/* it would be nice if this could auto-register itself in the
+	   constructor, since MidiControlUI is a singleton, but it can't be
+	   created until after the engine is running. Therefore we have to
+	   explicitly register it here.
+	*/
+	EventLoop::register_request_buffer_factory (X_("midiUI"), MidiControlUI::request_factory);
+
         ProcessThread::init ();
 	/* the + 4 is a bit of a handwave. i don't actually know
 	   how many more per-thread buffer sets we need above
@@ -553,8 +570,6 @@ ARDOUR::init (bool use_windows_vst, bool try_optimization, const char* localedir
 void
 ARDOUR::init_post_engine ()
 {
-	ControlProtocolManager::instance().discover_control_protocols ();
-
 	XMLNode* node;
 	if ((node = Config->control_protocol_state()) != 0) {
 		ControlProtocolManager::instance().set_state (*node, Stateful::loading_state_version);