diff -urpN Ardour-6.6.0.orig/gtk2_ardour/midi_tracer.cc Ardour-6.6.0/gtk2_ardour/midi_tracer.cc
--- Ardour-6.6.0.orig/gtk2_ardour/midi_tracer.cc	2021-02-22 10:41:53.000000000 -0800
+++ Ardour-6.6.0/gtk2_ardour/midi_tracer.cc	2021-04-22 03:29:24.330977741 -0700
@@ -53,7 +53,6 @@ MidiTracer::MidiTracer ()
 	, autoscroll (true)
 	, show_hex (true)
 	, show_delta_time (false)
-	, _update_queued (0)
 	, fifo (1024)
 	, buffer_pool ("miditracer", buffer_size, 1024) // 1024 256 byte buffers
 	, autoscroll_button (_("Auto-Scroll"))
@@ -61,6 +60,8 @@ MidiTracer::MidiTracer ()
 	, collect_button (_("Enabled"))
 	, delta_time_button (_("Delta times"))
 {
+	g_atomic_int_set (&_update_queued, 0);
+
 	ARDOUR::AudioEngine::instance()->PortRegisteredOrUnregistered.connect
 		(_manager_connection, invalidator (*this), boost::bind (&MidiTracer::ports_changed, this), gui_context());
 
@@ -407,9 +408,8 @@ MidiTracer::tracer (Parser&, byte* msg,
 
 	fifo.write (&buf, 1);
 
-	if (g_atomic_int_get (const_cast<gint*> (&_update_queued)) == 0) {
+	if (g_atomic_int_compare_and_exchange (&_update_queued, 0, 1)) {
 		gui_context()->call_slot (invalidator (*this), boost::bind (&MidiTracer::update, this));
-		g_atomic_int_inc (const_cast<gint*> (&_update_queued));
 	}
 }
 
@@ -417,7 +417,7 @@ void
 MidiTracer::update ()
 {
 	bool updated = false;
-	g_atomic_int_dec_and_test (const_cast<gint*> (&_update_queued));
+	g_atomic_int_set (&_update_queued, 0);
 
 	RefPtr<TextBuffer> buf (text.get_buffer());
 
diff -urpN Ardour-6.6.0.orig/gtk2_ardour/midi_tracer.h Ardour-6.6.0/gtk2_ardour/midi_tracer.h
--- Ardour-6.6.0.orig/gtk2_ardour/midi_tracer.h	2021-02-22 10:41:53.000000000 -0800
+++ Ardour-6.6.0/gtk2_ardour/midi_tracer.h	2021-04-22 03:29:24.330977741 -0700
@@ -34,6 +34,8 @@
 #include "pbd/signals.h"
 #include "pbd/ringbuffer.h"
 #include "pbd/pool.h"
+#include "pbd/g_atomic_compat.h"
+
 #include "midi++/types.h"
 #include "ardour_window.h"
 
@@ -68,7 +70,7 @@ private:
 	 *  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;
+	GATOMIC_QUAL gint _update_queued;
 
 	PBD::RingBuffer<char *> fifo;
 	Pool buffer_pool;
diff -urpN Ardour-6.6.0.orig/gtk2_ardour/public_editor.cc Ardour-6.6.0/gtk2_ardour/public_editor.cc
--- Ardour-6.6.0.orig/gtk2_ardour/public_editor.cc	2021-02-22 10:41:53.000000000 -0800
+++ Ardour-6.6.0/gtk2_ardour/public_editor.cc	2021-04-22 03:29:24.330977741 -0700
@@ -33,8 +33,8 @@ sigc::signal<void> PublicEditor::DropDow
 
 PublicEditor::PublicEditor (Gtk::Widget& content)
 	: Tabbable (content, _("Editor"), X_("editor"))
-	, _suspend_route_redisplay_counter (0)
 {
+	g_atomic_int_set (&_suspend_route_redisplay_counter, 0);
 }
 
 PublicEditor::~PublicEditor()
diff -urpN Ardour-6.6.0.orig/gtk2_ardour/public_editor.h Ardour-6.6.0/gtk2_ardour/public_editor.h
--- Ardour-6.6.0.orig/gtk2_ardour/public_editor.h	2021-02-22 10:41:53.000000000 -0800
+++ Ardour-6.6.0/gtk2_ardour/public_editor.h	2021-04-22 03:29:24.330977741 -0700
@@ -44,6 +44,7 @@
 #include <sigc++/signal.h>
 
 #include "pbd/statefuldestructible.h"
+#include "pbd/g_atomic_compat.h"
 
 #include "temporal/beats.h"
 
@@ -523,13 +524,14 @@ protected:
 	friend class DisplaySuspender;
 	virtual void suspend_route_redisplay () = 0;
 	virtual void resume_route_redisplay () = 0;
-	gint _suspend_route_redisplay_counter;
+
+	GATOMIC_QUAL gint _suspend_route_redisplay_counter;
 };
 
 class DisplaySuspender {
 	public:
 		DisplaySuspender() {
-			if (g_atomic_int_add(&PublicEditor::instance()._suspend_route_redisplay_counter, 1) == 0) {
+			if (g_atomic_int_add (&PublicEditor::instance()._suspend_route_redisplay_counter, 1) == 0) {
 				PublicEditor::instance().suspend_route_redisplay ();
 			}
 		}
diff -urpN Ardour-6.6.0.orig/gtk2_ardour/timers.cc Ardour-6.6.0/gtk2_ardour/timers.cc
--- Ardour-6.6.0.orig/gtk2_ardour/timers.cc	2021-02-22 10:41:53.000000000 -0800
+++ Ardour-6.6.0/gtk2_ardour/timers.cc	2021-04-22 03:29:24.330977741 -0700
@@ -22,6 +22,7 @@
 #include "pbd/timer.h"
 #include "pbd/debug.h"
 #include "pbd/compose.h"
+#include "pbd/g_atomic_compat.h"
 
 #include "debug.h"
 
@@ -87,8 +88,8 @@ public:
 		, rapid(100)
 		, super_rapid(40)
 		, fps(40)
-		, _suspend_counter(0)
 	{
+	g_atomic_int_set (&_suspend_counter, 0);
 #ifndef NDEBUG
 		second.connect (sigc::mem_fun (*this, &UITimers::on_second_timer));
 #endif
@@ -100,7 +101,7 @@ public:
 	StandardTimer   super_rapid;
 	StandardTimer   fps;
 
-	gint            _suspend_counter;
+	GATOMIC_QUAL gint _suspend_counter;
 
 #ifndef NDEBUG
 	std::vector<uint64_t> rapid_eps_count;
@@ -212,7 +213,7 @@ fps_connect(const sigc::slot<void>& slot
 
 TimerSuspender::TimerSuspender ()
 {
-	if (g_atomic_int_add(&get_timers()._suspend_counter, 1) == 0) {
+	if (g_atomic_int_add (&get_timers()._suspend_counter, 1) == 0) {
 		get_timers().rapid.suspend();
 		get_timers().super_rapid.suspend();
 		get_timers().fps.suspend();