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, 11 insertions, 4 deletions

diff --git a/libs/pbd/pthread_utils.cc b/libs/pbd/pthread_utils.cc
index 1abe6a95fb..7cd25e42b8 100644
--- a/libs/pbd/pthread_utils.cc
+++ b/libs/pbd/pthread_utils.cc
@@ -44,7 +44,7 @@ static pthread_mutex_t thread_map_lock = PTHREAD_MUTEX_INITIALIZER;
 static Glib::Threads::Private<char> thread_name (free);
 
 namespace PBD {
-	PBD::Signal4<void,std::string, pthread_t,std::string,uint32_t> ThreadCreatedWithRequestSize;
+	PBD::Signal3<void,pthread_t,std::string,uint32_t> ThreadCreatedWithRequestSize;
 }
 
 using namespace PBD;
@@ -58,10 +58,18 @@ static int thread_creator (pthread_t* thread_id, const pthread_attr_t* attr, voi
 #endif
 }
 
+
 void
-PBD::notify_gui_about_thread_creation (std::string target_gui, pthread_t thread, std::string str, int request_count)
+PBD::notify_event_loops_about_thread_creation (pthread_t thread, const std::string& emitting_thread_name, int request_count)
 {
-	ThreadCreatedWithRequestSize (target_gui, thread, str, request_count);
+	/* notify threads that may exist in the future (they may also exist
+	 * already, in which case they will catch the
+	 * ThreadCreatedWithRequestSize signal)
+	 */
+	EventLoop::pre_register (emitting_thread_name, request_count);
+
+	/* notify all existing threads */
+	ThreadCreatedWithRequestSize (thread, emitting_thread_name, request_count);
 }
 
 struct ThreadStartWithName {
@@ -199,4 +207,3 @@ pthread_cancel_one (pthread_t thread)
 	pthread_cancel (thread);
 	pthread_mutex_unlock (&thread_map_lock);
 }
-