Fix race causing MIDI tracer to stop working when master record state is changed.

git-svn-id: svn://localhost/ardour2/branches/3.0@7320 d708f5d6-7413-0410-9779-e7cbd77b26cf

2 files changed, 11 insertions, 5 deletions

diff --git a/gtk2_ardour/midi_tracer.cc b/gtk2_ardour/midi_tracer.cc
index a9f38b52ff..565d0f4911 100644
--- a/gtk2_ardour/midi_tracer.cc
+++ b/gtk2_ardour/midi_tracer.cc
@@ -25,7 +25,7 @@ MidiTracer::MidiTracer (const std::string& name, Parser& p)
 	, autoscroll (true)
 	, show_hex (true)
 	, collect (true)
-	, update_queued (false)
+	, _update_queued (0)
 	, fifo (1024)
 	, buffer_pool ("miditracer", buffer_size, 1024) // 1024 256 byte buffers
 	, autoscroll_button (_("Auto-Scroll"))
@@ -255,9 +255,9 @@ MidiTracer::tracer (Parser&, byte* msg, size_t len)
 
 	fifo.write (&buf, 1);
 
-	if (!update_queued) {
+	if (g_atomic_int_get (&_update_queued) == 0) {
 		gui_context()->call_slot (invalidator (*this), boost::bind (&MidiTracer::update, this));
-		update_queued = true;
+		g_atomic_int_inc (&_update_queued);
 	}
 }
 
@@ -265,7 +265,7 @@ void
 MidiTracer::update ()
 {
 	bool updated = false;
-	update_queued = false;
+	g_atomic_int_dec_and_test (&_update_queued);
 
 	RefPtr<TextBuffer> buf (text.get_buffer());
 
diff --git a/gtk2_ardour/midi_tracer.h b/gtk2_ardour/midi_tracer.h
index 47f1738243..fb5943370d 100644
--- a/gtk2_ardour/midi_tracer.h
+++ b/gtk2_ardour/midi_tracer.h
@@ -36,7 +36,13 @@ class MidiTracer : public ArdourDialog
 	bool autoscroll;
 	bool show_hex;
 	bool collect;
-	volatile bool update_queued;
+	
+	/** Incremented when an update is requested, decremented when one is handled; hence
+	 *  equal to 0 when an update is not queued.  May temporarily be negative if a
+	 *  update is handled before it was noted that it had just been queued.
+	 */
+	volatile gint _update_queued;
+	 
 	RingBuffer<char *> fifo;
 	Pool buffer_pool;
 	static const size_t buffer_size = 256;