diff --git a/client/CClient.cpp b/client/CClient.cpp
index ab221a7e..69e6026c 100644
--- a/client/CClient.cpp
+++ b/client/CClient.cpp
@@ -27,6 +27,7 @@ CClient::CClient(const CString& clientName) :
 	m_screen(NULL),
 	m_server(NULL),
 	m_camp(false),
+	m_session(NULL),
 	m_active(false),
 	m_rejected(true)
 {
@@ -64,6 +65,13 @@ CClient::wasRejected() const
 	return m_rejected;
 }
 
+void
+CClient::onError()
+{
+	// close down session but don't wait too long
+	deleteSession(3.0);
+}
+
 void
 CClient::onInfoChanged(const CClientInfo& info)
 {
@@ -144,28 +152,31 @@ CClient::run()
 		log((CLOG_NOTE "starting client \"%s\"", m_name.c_str()));
 
 		// start server interactions
-		thread = new CThread(new TMethodJob<CClient>(
+		{
+			CLock lock(&m_mutex);
+			m_session = new CThread(new TMethodJob<CClient>(
 								this, &CClient::runSession));
+		}
 
 		// handle events
 		m_screen->run();
 
 		// clean up
-		deleteSession(thread);
+		deleteSession();
 		log((CLOG_NOTE "stopping client \"%s\"", m_name.c_str()));
 	}
 	catch (XBase& e) {
 		log((CLOG_ERR "client error: %s", e.what()));
 
 		// clean up
-		deleteSession(thread);
+		deleteSession();
 		log((CLOG_NOTE "stopping client \"%s\"", m_name.c_str()));
 		CLock lock(&m_mutex);
 		m_rejected = false;
 	}
 	catch (XThread&) {
 		// clean up
-		deleteSession(thread);
+		deleteSession();
 		log((CLOG_NOTE "stopping client \"%s\"", m_name.c_str()));
 		throw;
 	}
@@ -173,7 +184,7 @@ CClient::run()
 		log((CLOG_DEBUG "unknown client error"));
 
 		// clean up
-		deleteSession(thread);
+		deleteSession();
 		log((CLOG_NOTE "stopping client \"%s\"", m_name.c_str()));
 		throw;
 	}
@@ -424,11 +435,20 @@ CClient::runSession(void*)
 }
 
 void
-CClient::deleteSession(CThread* thread)
+CClient::deleteSession(double timeout)
 {
+	// get session thread object
+	CThread* thread;
+	{
+		CLock lock(&m_mutex);
+		thread    = m_session;
+		m_session = NULL;
+	}
+
+	// shut it down
 	if (thread != NULL) {
 		thread->cancel();
-		thread->wait();
+		thread->wait(timeout);
 		delete thread;
 	}
 }
diff --git a/client/CClient.h b/client/CClient.h
index c555d87c..2e8e2256 100644
--- a/client/CClient.h
+++ b/client/CClient.h
@@ -39,6 +39,7 @@ public:
 	bool 				wasRejected() const;
 
 	// IScreenReceiver overrides
+	virtual void		onError();
 	virtual void		onInfoChanged(const CClientInfo&);
 	virtual bool		onGrabClipboard(ClipboardID);
 	virtual void		onClipboardChanged(ClipboardID, const CString&);
@@ -47,7 +48,6 @@ public:
 	virtual bool		open();
 	virtual void		run();
 	virtual void		close();
-// FIXME -- can we avoid passing everything here?
 	virtual void		enter(SInt32 xAbs, SInt32 yAbs,
 							UInt32 seqNum, KeyModifierMask mask,
 							bool forScreensaver);
@@ -80,7 +80,7 @@ private:
 
 	// handle server messaging
 	void				runSession(void*);
-	void				deleteSession(CThread*);
+	void				deleteSession(double timeout = -1.0);
 	void				runServer();
 	CServerProxy*		handshakeServer(IDataSocket*);
 
@@ -91,6 +91,7 @@ private:
 	IScreenReceiver*	m_server;
 	CNetworkAddress		m_serverAddress;
 	bool				m_camp;
+	CThread*			m_session;
 	bool				m_active;
 	bool				m_rejected;
 	bool				m_ownClipboard[kClipboardEnd];
diff --git a/client/CMSWindowsSecondaryScreen.cpp b/client/CMSWindowsSecondaryScreen.cpp
index 78b514f4..3c93ac0c 100644
--- a/client/CMSWindowsSecondaryScreen.cpp
+++ b/client/CMSWindowsSecondaryScreen.cpp
@@ -206,12 +206,6 @@ CMSWindowsSecondaryScreen::getScreen() const
 	return m_screen;
 }
 
-void
-CMSWindowsSecondaryScreen::onError()
-{
-	// ignore
-}
-
 void
 CMSWindowsSecondaryScreen::onScreensaver(bool)
 {
diff --git a/client/CMSWindowsSecondaryScreen.h b/client/CMSWindowsSecondaryScreen.h
index e9b956c7..b98a4251 100644
--- a/client/CMSWindowsSecondaryScreen.h
+++ b/client/CMSWindowsSecondaryScreen.h
@@ -33,7 +33,6 @@ public:
 	virtual IScreen*	getScreen() const;
 
 	// IMSWindowsScreenEventHandler overrides
-	virtual void		onError();
 	virtual void		onScreensaver(bool activated);
 	virtual bool		onPreDispatch(const CEvent* event);
 	virtual bool		onEvent(CEvent* event);
diff --git a/client/CSecondaryScreen.cpp b/client/CSecondaryScreen.cpp
index a19bc4e4..9452ffae 100644
--- a/client/CSecondaryScreen.cpp
+++ b/client/CSecondaryScreen.cpp
@@ -18,13 +18,6 @@ CSecondaryScreen::~CSecondaryScreen()
 	// do nothing
 }
 
-bool
-CSecondaryScreen::isActive() const
-{
-	CLock lock(&m_mutex);
-	return m_active;
-}
-
 void
 CSecondaryScreen::run()
 {
@@ -85,7 +78,10 @@ CSecondaryScreen::open()
 	}
 
 	// hide the cursor
-	m_active = true;
+	{
+		CLock lock(&m_mutex);
+		m_active = true;
+	}
 	leave();
 }
 
@@ -175,6 +171,13 @@ CSecondaryScreen::screensaver(bool activate)
 	getScreen()->screensaver(activate);
 }
 
+bool
+CSecondaryScreen::isActive() const
+{
+	CLock lock(&m_mutex);
+	return m_active;
+}
+
 void
 CSecondaryScreen::getClipboard(ClipboardID id,
 				IClipboard* clipboard) const
diff --git a/client/CServerProxy.cpp b/client/CServerProxy.cpp
index 2aa59a4a..b8a9a3b3 100644
--- a/client/CServerProxy.cpp
+++ b/client/CServerProxy.cpp
@@ -221,6 +221,12 @@ CServerProxy::getOutputStream() const
 	return m_output;
 }
 
+void
+CServerProxy::onError()
+{
+	// ignore
+}
+
 void
 CServerProxy::onInfoChanged(const CClientInfo& info)
 {
diff --git a/client/CServerProxy.h b/client/CServerProxy.h
index 0370a646..e7f48d19 100644
--- a/client/CServerProxy.h
+++ b/client/CServerProxy.h
@@ -34,6 +34,7 @@ public:
 	IOutputStream*		getOutputStream() const;
 
 	// IScreenReceiver overrides
+	virtual void		onError();
 	virtual void		onInfoChanged(const CClientInfo&);
 	virtual bool		onGrabClipboard(ClipboardID);
 	virtual void		onClipboardChanged(ClipboardID, const CString& data);
diff --git a/client/CXWindowsSecondaryScreen.cpp b/client/CXWindowsSecondaryScreen.cpp
index d8e5ab66..b0187ccb 100644
--- a/client/CXWindowsSecondaryScreen.cpp
+++ b/client/CXWindowsSecondaryScreen.cpp
@@ -145,13 +145,6 @@ CXWindowsSecondaryScreen::getScreen() const
 	return m_screen;
 }
 
-void
-CXWindowsSecondaryScreen::onError()
-{
-	// ignore
-	// FIXME -- forward this?  to whom?
-}
-
 void
 CXWindowsSecondaryScreen::onScreensaver(bool)
 {
@@ -273,16 +266,18 @@ CXWindowsSecondaryScreen::createWindow()
 void
 CXWindowsSecondaryScreen::destroyWindow()
 {
-	CDisplayLock display(m_screen);
-	if (display != NULL) {
-		// release keys that are still pressed
-		releaseKeys(display);
+	{
+		CDisplayLock display(m_screen);
+		if (display != NULL) {
+			// release keys that are still pressed
+			releaseKeys(display);
 
-		// no longer impervious to server grabs
-		XTestGrabControl(display, False);
+			// no longer impervious to server grabs
+			XTestGrabControl(display, False);
 
-		// update
-		XSync(display, False);
+			// update
+			XSync(display, False);
+		}
 	}
 
 	// destroy window
diff --git a/client/CXWindowsSecondaryScreen.h b/client/CXWindowsSecondaryScreen.h
index 6237996b..07ddb346 100644
--- a/client/CXWindowsSecondaryScreen.h
+++ b/client/CXWindowsSecondaryScreen.h
@@ -31,7 +31,6 @@ public:
 	virtual IScreen*	getScreen() const;
 
 	// IScreenEventHandler overrides
-	virtual void		onError();
 	virtual void		onScreensaver(bool activated);
 	virtual bool		onPreDispatch(const CEvent* event);
 	virtual bool		onEvent(CEvent* event);
diff --git a/platform/CXWindowsScreen.cpp b/platform/CXWindowsScreen.cpp
index ed573cbf..5ae7f31e 100644
--- a/platform/CXWindowsScreen.cpp
+++ b/platform/CXWindowsScreen.cpp
@@ -656,7 +656,7 @@ CXWindowsScreen::ioErrorHandler(Display*)
 	// so we set it to NULL), and exit.
 	log((CLOG_WARN "X display has unexpectedly disconnected"));
 	s_screen->m_display = NULL;
-	s_screen->m_eventHandler->onError();
+	s_screen->m_receiver->onError();
 	log((CLOG_CRIT "quiting due to X display disconnection"));
 	exit(17);
 }
diff --git a/platform/IMSWindowsScreenEventHandler.h b/platform/IMSWindowsScreenEventHandler.h
index 33804a96..eb39542b 100755
--- a/platform/IMSWindowsScreenEventHandler.h
+++ b/platform/IMSWindowsScreenEventHandler.h
@@ -16,7 +16,6 @@ public:
 	virtual void		preDestroyWindow(HWND) = 0;
 
 	// IScreenEventHandler overrides
-	virtual void		onError() = 0;
 	virtual void		onScreensaver(bool activated) = 0;
 	virtual bool		onPreDispatch(const CEvent* event) = 0;
 	virtual bool		onEvent(CEvent* event) = 0;
diff --git a/server/CMSWindowsPrimaryScreen.cpp b/server/CMSWindowsPrimaryScreen.cpp
index 3906bcaf..d2e53b6f 100644
--- a/server/CMSWindowsPrimaryScreen.cpp
+++ b/server/CMSWindowsPrimaryScreen.cpp
@@ -145,12 +145,6 @@ CMSWindowsPrimaryScreen::getScreen() const
 	return m_screen;
 }
 
-void
-CMSWindowsPrimaryScreen::onError()
-{
-	// ignore
-}
-
 void
 CMSWindowsPrimaryScreen::onScreensaver(bool activated)
 {
diff --git a/server/CMSWindowsPrimaryScreen.h b/server/CMSWindowsPrimaryScreen.h
index 5414d633..0b8af7b1 100644
--- a/server/CMSWindowsPrimaryScreen.h
+++ b/server/CMSWindowsPrimaryScreen.h
@@ -27,7 +27,6 @@ public:
 	virtual IScreen*	getScreen() const;
 
 	// IMSWindowsScreenEventHandler overrides
-	virtual void		onError();
 	virtual void		onScreensaver(bool activated);
 	virtual bool		onPreDispatch(const CEvent* event);
 	virtual bool		onEvent(CEvent* event);
diff --git a/server/CPrimaryClient.cpp b/server/CPrimaryClient.cpp
index 89668c22..56bd3464 100644
--- a/server/CPrimaryClient.cpp
+++ b/server/CPrimaryClient.cpp
@@ -69,6 +69,13 @@ CPrimaryClient::getToggleMask() const
 	return m_screen->getToggleMask();
 }
 
+void
+CPrimaryClient::onError()
+{
+	// forward to server
+	m_server->onError();
+}
+
 void
 CPrimaryClient::onInfoChanged(const CClientInfo& info)
 {
@@ -79,9 +86,7 @@ CPrimaryClient::onInfoChanged(const CClientInfo& info)
 bool
 CPrimaryClient::onGrabClipboard(ClipboardID id)
 {
-	bool result = m_server->onGrabClipboard(getName(), id, m_seqNum);
-	m_clipboardOwner[id] = result;
-	return result;
+	return m_server->onGrabClipboard(getName(), id, m_seqNum);
 }
 
 void
@@ -93,9 +98,8 @@ CPrimaryClient::onClipboardChanged(ClipboardID id, const CString& data)
 bool
 CPrimaryClient::open()
 {
-	// all clipboards are clean and owned by us
+	// all clipboards are clean
 	for (UInt32 i = 0; i < kClipboardEnd; ++i) {
-		m_clipboardOwner[i] = true;
 		m_clipboardDirty[i] = false;
 	}
 
@@ -159,7 +163,6 @@ CPrimaryClient::grabClipboard(ClipboardID id)
 	m_screen->grabClipboard(id);
 
 	// clipboard is dirty (because someone else owns it now)
-	m_clipboardOwner[id] = false;
 	m_clipboardDirty[id] = true;
 }
 
diff --git a/server/CPrimaryClient.h b/server/CPrimaryClient.h
index 3605a8e1..a94da39e 100644
--- a/server/CPrimaryClient.h
+++ b/server/CPrimaryClient.h
@@ -35,6 +35,7 @@ public:
 	KeyModifierMask		getToggleMask() const;
 
 	// IScreenReceiver overrides
+	virtual void		onError();
 	virtual void		onInfoChanged(const CClientInfo&);
 	virtual bool		onGrabClipboard(ClipboardID);
 	virtual void		onClipboardChanged(ClipboardID, const CString&);
@@ -71,7 +72,6 @@ private:
 	CString				m_name;
 	UInt32				m_seqNum;
 	CClientInfo			m_info;
-	bool				m_clipboardOwner[kClipboardEnd]; // FIXME -- unneeded?
 	bool				m_clipboardDirty[kClipboardEnd];
 };
 
diff --git a/server/CPrimaryScreen.cpp b/server/CPrimaryScreen.cpp
index a649a227..4184c7fd 100644
--- a/server/CPrimaryScreen.cpp
+++ b/server/CPrimaryScreen.cpp
@@ -2,11 +2,10 @@
 #include "IScreen.h"
 #include "IScreenReceiver.h"
 #include "ProtocolTypes.h"
+#include "CLock.h"
 #include "CThread.h"
 #include "CLog.h"
 
-// FIXME -- should be locking
-
 //
 // CPrimaryScreen
 //
@@ -84,7 +83,10 @@ CPrimaryScreen::open()
 	}
 
 	// enter the screen
-	enterNoWarp();
+	{
+		CLock lock(&m_mutex);
+		enterNoWarp();
+	}
 
 	// send screen info
 	m_receiver->onInfoChanged(info);
@@ -104,6 +106,7 @@ void
 CPrimaryScreen::enter(SInt32 x, SInt32 y, bool forScreensaver)
 {
 	log((CLOG_INFO "entering primary at %d,%d%s", x, y, forScreensaver ? " for screen saver" : ""));
+	CLock lock(&m_mutex);
 	assert(m_active == true);
 
 	enterNoWarp();
@@ -118,6 +121,8 @@ CPrimaryScreen::enter(SInt32 x, SInt32 y, bool forScreensaver)
 void
 CPrimaryScreen::enterNoWarp()
 {
+	// note -- must be locked on entry
+
 	// not active anymore
 	m_active = false;
 
@@ -135,6 +140,7 @@ bool
 CPrimaryScreen::leave()
 {
 	log((CLOG_INFO "leaving primary"));
+	CLock lock(&m_mutex);
 	assert(m_active == false);
 
 	// subclass hook
@@ -187,6 +193,7 @@ CPrimaryScreen::grabClipboard(ClipboardID id)
 bool
 CPrimaryScreen::isActive() const
 {
+	CLock lock(&m_mutex);
 	return m_active;
 }
 
diff --git a/server/CPrimaryScreen.h b/server/CPrimaryScreen.h
index 9040222d..5df1987c 100644
--- a/server/CPrimaryScreen.h
+++ b/server/CPrimaryScreen.h
@@ -3,6 +3,7 @@
 
 #include "ClipboardTypes.h"
 #include "KeyTypes.h"
+#include "CMutex.h"
 
 class IClipboard;
 class IScreen;
@@ -146,8 +147,9 @@ private:
 	void				enterNoWarp();
 
 private:
-	// FIXME -- should have a mutex
+	CMutex				m_mutex;
 
+	// object to notify of changes
 	IScreenReceiver*	m_receiver;
 
 	// m_active is true if this screen has been left
diff --git a/server/CServer.cpp b/server/CServer.cpp
index 1491f6c1..d10606b1 100644
--- a/server/CServer.cpp
+++ b/server/CServer.cpp
@@ -212,6 +212,20 @@ CServer::getActivePrimarySides() const
 	return sides;
 }
 
+void
+CServer::onError()
+{
+	// stop all running threads but don't wait too long since some
+	// threads may be unable to proceed until this thread returns.
+	stopThreads(3.0);
+
+	// done with the HTTP server
+	delete m_httpServer;
+	m_httpServer = NULL;
+
+	// note -- we do not attempt to close down the primary screen
+}
+
 void
 CServer::onInfoChanged(const CString& name, const CClientInfo& info)
 {
@@ -334,20 +348,6 @@ CServer::onClipboardChangedNoLock(ClipboardID id,
 	m_active->setClipboard(id, m_clipboards[id].m_clipboardData);
 }
 
-void
-CServer::onError()
-{
-	// stop all running threads but don't wait too long since some
-	// threads may be unable to proceed until this thread returns.
-	stopThreads(3.0);
-
-	// done with the HTTP server
-	delete m_httpServer;
-	m_httpServer = NULL;
-
-	// note -- we do not attempt to close down the primary screen
-}
-
 void
 CServer::onScreensaver(bool activated)
 {
diff --git a/server/CServer.h b/server/CServer.h
index b8d49038..734d8906 100644
--- a/server/CServer.h
+++ b/server/CServer.h
@@ -55,12 +55,12 @@ public:
 	CString				getPrimaryScreenName() const;
 
 	// IServer overrides
+	virtual void		onError();
 	virtual void		onInfoChanged(const CString&, const CClientInfo&);
 	virtual bool		onGrabClipboard(const CString&, ClipboardID, UInt32);
 	virtual void		onClipboardChanged(ClipboardID, UInt32, const CString&);
 
 	// IPrimaryScreenReceiver overrides
-	virtual void		onError();
 	virtual void		onScreensaver(bool activated);
 	virtual void		onKeyDown(KeyID, KeyModifierMask);
 	virtual void		onKeyUp(KeyID, KeyModifierMask);
diff --git a/server/CXWindowsPrimaryScreen.cpp b/server/CXWindowsPrimaryScreen.cpp
index 1f7fa7b1..1e75254e 100644
--- a/server/CXWindowsPrimaryScreen.cpp
+++ b/server/CXWindowsPrimaryScreen.cpp
@@ -132,13 +132,6 @@ CXWindowsPrimaryScreen::getScreen() const
 	return m_screen;
 }
 
-void
-CXWindowsPrimaryScreen::onError()
-{
-	// tell server to shutdown
-	m_receiver->onError();
-}
-
 void
 CXWindowsPrimaryScreen::onScreensaver(bool activated)
 {
diff --git a/server/CXWindowsPrimaryScreen.h b/server/CXWindowsPrimaryScreen.h
index 2a97a51c..ad625ff7 100644
--- a/server/CXWindowsPrimaryScreen.h
+++ b/server/CXWindowsPrimaryScreen.h
@@ -28,7 +28,6 @@ public:
 	virtual IScreen*	getScreen() const;
 
 	// IScreenEventHandler overrides
-	virtual void		onError();
 	virtual void		onScreensaver(bool activated);
 	virtual bool		onPreDispatch(const CEvent* event);
 	virtual bool		onEvent(CEvent* event);
diff --git a/synergy/IPrimaryScreenReceiver.h b/synergy/IPrimaryScreenReceiver.h
index ff816928..f347786e 100644
--- a/synergy/IPrimaryScreenReceiver.h
+++ b/synergy/IPrimaryScreenReceiver.h
@@ -11,13 +11,6 @@
 // an IPrimaryScreenReceiver* and notify it of events.
 class IPrimaryScreenReceiver : public IInterface {
 public:
-	// called if the display is unexpectedly closing.
-
-	// called if the screen is unexpectedly closing.  this implies that
-	// the screen is no longer usable and that the program should
-	// close the screen and possibly terminate.
-	virtual void		onError() = 0;
-
 	// called when the screensaver is activated or deactivated
 	virtual void		onScreensaver(bool activated) = 0;
 
diff --git a/synergy/IScreen.h b/synergy/IScreen.h
index 861f69c5..08c337ab 100644
--- a/synergy/IScreen.h
+++ b/synergy/IScreen.h
@@ -43,7 +43,10 @@ public:
 	// activate or deactivate the screen saver
 	virtual void		screensaver(bool activate) = 0;
 
-	// FIXME -- need explanation
+	// ensure that this thread attached with the visible desktop.  this is
+	// mainly intended for windows which has an artificial distinction
+	// between desktops and a thread cannot interact with the visible
+	// desktop unless the thread is attached to that desktop.
 	virtual void		syncDesktop() = 0;
 
 	// accessors
@@ -58,8 +61,9 @@ public:
 	// get the current cursor coordinates
 	virtual void		getCursorPos(SInt32& x, SInt32& y) const = 0;
 
-	// get the cursor center position
-	// FIXME -- need better explanation
+	// get the cursor center position.  this is where we park the
+	// cursor to compute cursor motion deltas and should be far from
+	// the edges of the screen, typically the center.
 	virtual void		getCursorCenter(SInt32& x, SInt32& y) const = 0;
 };
 
diff --git a/synergy/IScreenEventHandler.h b/synergy/IScreenEventHandler.h
index 123956be..4c6cd14e 100644
--- a/synergy/IScreenEventHandler.h
+++ b/synergy/IScreenEventHandler.h
@@ -18,11 +18,6 @@ class IScreenEventHandler : public IInterface {
 public:
 	// manipulators
 
-	// called if the screen is unexpectedly closing.  this implies that
-	// the screen is no longer usable and that the program should
-	// close the screen and possibly terminate.
-	virtual void		onError() = 0;
-
 	// called when the screensaver is activated or deactivated
 	virtual void		onScreensaver(bool activated) = 0;
 
diff --git a/synergy/IScreenReceiver.h b/synergy/IScreenReceiver.h
index 02fcf936..da2d40c9 100644
--- a/synergy/IScreenReceiver.h
+++ b/synergy/IScreenReceiver.h
@@ -10,6 +10,11 @@
 // notifications (indirectly) from the system.
 class IScreenReceiver : public IInterface {
 public:
+	// called if the screen is unexpectedly closing.  this implies that
+	// the screen is no longer usable and that the program should
+	// close the screen and possibly terminate.
+	virtual void		onError() = 0;
+
 	// notify of client info change
 	virtual void		onInfoChanged(const CClientInfo&) = 0;
 
diff --git a/synergy/IServer.h b/synergy/IServer.h
index f6a4e458..ee3798d6 100644
--- a/synergy/IServer.h
+++ b/synergy/IServer.h
@@ -17,6 +17,11 @@ class IServer : public IInterface {
 public:
 	// manipulators
 
+	// called if the screen is unexpectedly closing.  this implies that
+	// the screen is no longer usable and that the program should
+	// close the screen and possibly terminate.
+	virtual void		onError() = 0;
+
 	// notify of client info change
 	virtual void		onInfoChanged(const CString& clientName,
 							const CClientInfo&) = 0;