diff --git a/gtk2_ardour/audio_region_editor.cc b/gtk2_ardour/audio_region_editor.cc
index e47f145c7e..806659b52c 100644
--- a/gtk2_ardour/audio_region_editor.cc
+++ b/gtk2_ardour/audio_region_editor.cc
@@ -53,8 +53,8 @@ _peak_amplitude_thread (void* arg)
 AudioRegionEditor::AudioRegionEditor (Session* s, boost::shared_ptr<AudioRegion> r)
 	: RegionEditor (s, r)
 	, _audio_region (r)
-	, gain_adjustment(accurate_coefficient_to_dB(_audio_region->scale_amplitude()), -40.0, +40.0, 0.1, 1.0, 0)	  
-	, _peak_amplitude_found (false)
+	, gain_adjustment(accurate_coefficient_to_dB(_audio_region->scale_amplitude()), -40.0, +40.0, 0.1, 1.0, 0)
+	, _peak_channel (false)
 {
 
 	Gtk::HBox* b = Gtk::manage (new Gtk::HBox);
@@ -91,6 +91,7 @@ AudioRegionEditor::AudioRegionEditor (Session* s, boost::shared_ptr<AudioRegion>
 
 	PeakAmplitudeFound.connect (_peak_amplitude_connection, invalidator (*this), boost::bind (&AudioRegionEditor::peak_amplitude_found, this, _1), gui_context ());
 	pthread_create_and_store (X_("peak-amplitude"), &_peak_amplitude_thread_handle, _peak_amplitude_thread, this);
+	_peak_channel.deliver ('c');
 }
 
 AudioRegionEditor::~AudioRegionEditor ()
@@ -109,6 +110,11 @@ AudioRegionEditor::region_changed (const PBD::PropertyChange& what_changed)
 	if (what_changed.contains (ARDOUR::Properties::scale_amplitude)) {
 		gain_changed ();
 	}
+
+	if (what_changed.contains (ARDOUR::Properties::start) || what_changed.contains (ARDOUR::Properties::length)) {
+		/* ask the peak thread to run again */
+		_peak_channel.deliver ('c');
+	}
 }
 void
 AudioRegionEditor::gain_changed ()
@@ -131,7 +137,14 @@ AudioRegionEditor::gain_adjustment_changed ()
 void
 AudioRegionEditor::peak_amplitude_thread ()
 {
-	PeakAmplitudeFound (accurate_coefficient_to_dB (_audio_region->maximum_amplitude ())); /* EMIT SIGNAL */
+	while (1) {
+		/* await instructions to run */
+		char msg;
+		_peak_channel.receive (msg);
+
+		/* compute peak amplitude and signal the fact */
+		PeakAmplitudeFound (accurate_coefficient_to_dB (_audio_region->maximum_amplitude ())); /* EMIT SIGNAL */
+	}
 }
 
 void
diff --git a/gtk2_ardour/audio_region_editor.h b/gtk2_ardour/audio_region_editor.h
index f3accaf115..5c9e56d923 100644
--- a/gtk2_ardour/audio_region_editor.h
+++ b/gtk2_ardour/audio_region_editor.h
@@ -37,6 +37,7 @@
 #include <libgnomecanvas/libgnomecanvas.h>
 
 #include "pbd/signals.h"
+#include "pbd/crossthread.h"
 
 #include "audio_clock.h"
 #include "ardour_dialog.h"
@@ -73,11 +74,11 @@ class AudioRegionEditor : public RegionEditor
 	Gtk::Label _peak_amplitude_label;
 	Gtk::Entry _peak_amplitude;
 
-	bool _peak_amplitude_found;
 	pthread_t _peak_amplitude_thread_handle;
 	void peak_amplitude_found (double);
 	PBD::Signal1<void, double> PeakAmplitudeFound;
 	PBD::ScopedConnection _peak_amplitude_connection;
+	CrossThreadChannel _peak_channel;
 };
 
 #endif /* __gtk_ardour_audio_region_edit_h__ */
diff --git a/libs/midi++2/port.cc b/libs/midi++2/port.cc
index 539d5c49cb..59f76041d6 100644
--- a/libs/midi++2/port.cc
+++ b/libs/midi++2/port.cc
@@ -50,6 +50,7 @@ Port::Port (string const & name, Flags flags, jack_client_t* jack_client)
 	, _jack_client (jack_client)
 	, _jack_port (0)
 	, _last_read_index (0)
+	, xthread (true)
 	, output_fifo (512)
 	, input_fifo (1024)
 	, _flags (flags)
@@ -64,6 +65,7 @@ Port::Port (const XMLNode& node, jack_client_t* jack_client)
 	, _jack_client (jack_client)
 	, _jack_port (0)
 	, _last_read_index (0)
+	, xthread (true)
 	, output_fifo (512)
 	, input_fifo (1024)
 {
diff --git a/libs/pbd/base_ui.cc b/libs/pbd/base_ui.cc
index ce7018a005..d56e4a31a4 100644
--- a/libs/pbd/base_ui.cc
+++ b/libs/pbd/base_ui.cc
@@ -41,7 +41,8 @@ BaseUI::RequestType BaseUI::CallSlot = BaseUI::new_request_type();
 BaseUI::RequestType BaseUI::Quit = BaseUI::new_request_type();
 
 BaseUI::BaseUI (const string& str)
-	: run_loop_thread (0)
+	: request_channel (true)
+	, run_loop_thread (0)
 	, _name (str)
 {
 	base_ui_instance = this;
diff --git a/libs/pbd/crossthread.cc b/libs/pbd/crossthread.cc
index 12ca19b945..553c8d52f3 100644
--- a/libs/pbd/crossthread.cc
+++ b/libs/pbd/crossthread.cc
@@ -30,7 +30,7 @@ using namespace std;
 using namespace PBD;
 using namespace Glib;
 
-CrossThreadChannel::CrossThreadChannel ()
+CrossThreadChannel::CrossThreadChannel (bool non_blocking)
 {
 	_ios = 0;
 	fds[0] = -1;
@@ -41,14 +41,16 @@ CrossThreadChannel::CrossThreadChannel ()
 		return;
 	}
 
-	if (fcntl (fds[0], F_SETFL, O_NONBLOCK)) {
-		error << "cannot set non-blocking mode for x-thread pipe (read) (" << ::strerror (errno) << ')' << endmsg;
-		return;
-	}
-
-	if (fcntl (fds[1], F_SETFL, O_NONBLOCK)) {
-		error << "cannot set non-blocking mode for x-thread pipe (write) (%2)" << ::strerror (errno) << ')' << endmsg;
-		return;
+	if (non_blocking) {
+		if (fcntl (fds[0], F_SETFL, O_NONBLOCK)) {
+			error << "cannot set non-blocking mode for x-thread pipe (read) (" << ::strerror (errno) << ')' << endmsg;
+			return;
+		}
+		
+		if (fcntl (fds[1], F_SETFL, O_NONBLOCK)) {
+			error << "cannot set non-blocking mode for x-thread pipe (write) (%2)" << ::strerror (errno) << ')' << endmsg;
+			return;
+		}
 	}
 }
 
diff --git a/libs/pbd/pbd/crossthread.h b/libs/pbd/pbd/crossthread.h
index f16cab9405..a791be5798 100644
--- a/libs/pbd/pbd/crossthread.h
+++ b/libs/pbd/pbd/crossthread.h
@@ -28,7 +28,7 @@
 
 class CrossThreadChannel { 
   public:
-	CrossThreadChannel();
+	CrossThreadChannel(bool);
 	~CrossThreadChannel();
 	
 	void wakeup();