Index: doc/Notifier.3
==================================================================
--- doc/Notifier.3
+++ doc/Notifier.3
@@ -88,13 +88,14 @@
 is NULL, it means there is no maximum wait time:  wait forever if
 necessary.
 .AP Tcl_Event *evPtr in
 An event to add to the event queue.  The storage for the event must
 have been allocated by the caller using \fBTcl_Alloc\fR or \fBckalloc\fR.
-.AP Tcl_QueuePosition position in
+.AP int flags in
 Where to add the new event in the queue:  \fBTCL_QUEUE_TAIL\fR,
-\fBTCL_QUEUE_HEAD\fR, or \fBTCL_QUEUE_MARK\fR.
+\fBTCL_QUEUE_HEAD\fR, \fBTCL_QUEUE_MARK\fR, and whether to do
+an alert if the queue is empty: \fBTCL_QUEUE_ALERT_IF_EMPTY\fR.
 .AP Tcl_ThreadId threadId in
 A unique identifier for a thread.
 .AP Tcl_EventDeleteProc *deleteProc in
 Procedure to invoke for each queued event in \fBTcl_DeleteEvents\fR.
 .AP int flags in
@@ -338,25 +339,29 @@
 The \fInextPtr\fR is used to link together the events in the queue
 and should not be modified by the event source.
 .PP
 An event may be added to the queue at any of three positions, depending
 on the \fIposition\fR argument to \fBTcl_QueueEvent\fR:
-.IP \fBTCL_QUEUE_TAIL\fR 24
+.IP \fBTCL_QUEUE_TAIL\fR 32
 Add the event at the back of the queue, so that all other pending
 events will be serviced first.  This is almost always the right
 place for new events.
-.IP \fBTCL_QUEUE_HEAD\fR 24
+.IP \fBTCL_QUEUE_HEAD\fR 32
 Add the event at the front of the queue, so that it will be serviced
 before all other queued events.
-.IP \fBTCL_QUEUE_MARK\fR 24
+.IP \fBTCL_QUEUE_MARK\fR 32
 Add the event at the front of the queue, unless there are other
 events at the front whose position is \fBTCL_QUEUE_MARK\fR;  if so,
 add the new event just after all other \fBTCL_QUEUE_MARK\fR events.
 This value of \fIposition\fR is used to insert an ordered sequence of
 events at the front of the queue, such as a series of
 Enter and Leave events synthesized during a grab or ungrab operation
 in Tk.
+.IP \fBTCL_QUEUE_ALERT_IF_EMPTY\fR 32
+When used in \fBTcl_ThreadQueueEvent\fR
+arranges for an automatic call of \fBTcl_ThreadAlert\fR when the queue was
+empty.
 .PP
 When it is time to handle an event from the queue (steps 1 and 4
 above) \fBTcl_ServiceEvent\fR will invoke the \fIproc\fR specified
 in the first queued \fBTcl_Event\fR structure.
 \fIProc\fR must match the following prototype:

Index: generic/tcl.decls
==================================================================
--- generic/tcl.decls
+++ generic/tcl.decls
@@ -732,11 +732,11 @@
 }
 declare 204 {
     const char *Tcl_PosixError(Tcl_Interp *interp)
 }
 declare 205 {
-    void Tcl_QueueEvent(Tcl_Event *evPtr, Tcl_QueuePosition position)
+    void Tcl_QueueEvent(Tcl_Event *evPtr, int flags)
 }
 declare 206 {
     int Tcl_Read(Tcl_Channel chan, char *bufPtr, int toRead)
 }
 declare 207 {
@@ -1142,11 +1142,11 @@
 declare 318 {
     void Tcl_ThreadAlert(Tcl_ThreadId threadId)
 }
 declare 319 {
     void Tcl_ThreadQueueEvent(Tcl_ThreadId threadId, Tcl_Event *evPtr,
-	    Tcl_QueuePosition position)
+	    int flags)
 }
 declare 320 {
     int Tcl_UniCharAtIndex(const char *src, int index)
 }
 declare 321 {

Index: generic/tcl.h
==================================================================
--- generic/tcl.h
+++ generic/tcl.h
@@ -1330,15 +1330,16 @@
     Tcl_EventProc *proc;	/* Function to call to service this event. */
     struct Tcl_Event *nextPtr;	/* Next in list of pending events, or NULL. */
 };
 
 /*
- * Positions to pass to Tcl_QueueEvent:
+ * Positions to pass to Tcl_QueueEvent/Tcl_ThreadQueueEvent:
  */
 
 typedef enum {
-    TCL_QUEUE_TAIL, TCL_QUEUE_HEAD, TCL_QUEUE_MARK
+    TCL_QUEUE_TAIL, TCL_QUEUE_HEAD, TCL_QUEUE_MARK,
+	    TCL_QUEUE_ALERT_IF_EMPTY=4
 } Tcl_QueuePosition;
 
 /*
  * Values to pass to Tcl_SetServiceMode to specify the behavior of notifier
  * event routines.

Index: generic/tclDecls.h
==================================================================
--- generic/tclDecls.h
+++ generic/tclDecls.h
@@ -644,12 +644,11 @@
 /* 203 */
 EXTERN int		Tcl_PutEnv(const char *assignment);
 /* 204 */
 EXTERN const char *	Tcl_PosixError(Tcl_Interp *interp);
 /* 205 */
-EXTERN void		Tcl_QueueEvent(Tcl_Event *evPtr,
-				Tcl_QueuePosition position);
+EXTERN void		Tcl_QueueEvent(Tcl_Event *evPtr, int flags);
 /* 206 */
 EXTERN int		Tcl_Read(Tcl_Channel chan, char *bufPtr, int toRead);
 /* 207 */
 EXTERN void		Tcl_ReapDetachedProcs(void);
 /* 208 */
@@ -985,11 +984,11 @@
 				int flags);
 /* 318 */
 EXTERN void		Tcl_ThreadAlert(Tcl_ThreadId threadId);
 /* 319 */
 EXTERN void		Tcl_ThreadQueueEvent(Tcl_ThreadId threadId,
-				Tcl_Event *evPtr, Tcl_QueuePosition position);
+				Tcl_Event *evPtr, int flags);
 /* 320 */
 EXTERN int		Tcl_UniCharAtIndex(const char *src, int index);
 /* 321 */
 EXTERN int		Tcl_UniCharToLower(int ch);
 /* 322 */
@@ -2228,11 +2227,11 @@
     Tcl_Channel (*tcl_OpenTcpServer) (Tcl_Interp *interp, int port, const char *host, Tcl_TcpAcceptProc *acceptProc, ClientData callbackData); /* 200 */
     void (*tcl_Preserve) (ClientData data); /* 201 */
     void (*tcl_PrintDouble) (Tcl_Interp *interp, double value, char *dst); /* 202 */
     int (*tcl_PutEnv) (const char *assignment); /* 203 */
     const char * (*tcl_PosixError) (Tcl_Interp *interp); /* 204 */
-    void (*tcl_QueueEvent) (Tcl_Event *evPtr, Tcl_QueuePosition position); /* 205 */
+    void (*tcl_QueueEvent) (Tcl_Event *evPtr, int flags); /* 205 */
     int (*tcl_Read) (Tcl_Channel chan, char *bufPtr, int toRead); /* 206 */
     void (*tcl_ReapDetachedProcs) (void); /* 207 */
     int (*tcl_RecordAndEval) (Tcl_Interp *interp, const char *cmd, int flags); /* 208 */
     int (*tcl_RecordAndEvalObj) (Tcl_Interp *interp, Tcl_Obj *cmdPtr, int flags); /* 209 */
     void (*tcl_RegisterChannel) (Tcl_Interp *interp, Tcl_Channel chan); /* 210 */
@@ -2342,11 +2341,11 @@
     void (*tcl_RestoreResult) (Tcl_Interp *interp, Tcl_SavedResult *statePtr); /* 314 */
     void (*tcl_SaveResult) (Tcl_Interp *interp, Tcl_SavedResult *statePtr); /* 315 */
     int (*tcl_SetSystemEncoding) (Tcl_Interp *interp, const char *name); /* 316 */
     Tcl_Obj * (*tcl_SetVar2Ex) (Tcl_Interp *interp, const char *part1, const char *part2, Tcl_Obj *newValuePtr, int flags); /* 317 */
     void (*tcl_ThreadAlert) (Tcl_ThreadId threadId); /* 318 */
-    void (*tcl_ThreadQueueEvent) (Tcl_ThreadId threadId, Tcl_Event *evPtr, Tcl_QueuePosition position); /* 319 */
+    void (*tcl_ThreadQueueEvent) (Tcl_ThreadId threadId, Tcl_Event *evPtr, int flags); /* 319 */
     int (*tcl_UniCharAtIndex) (const char *src, int index); /* 320 */
     int (*tcl_UniCharToLower) (int ch); /* 321 */
     int (*tcl_UniCharToTitle) (int ch); /* 322 */
     int (*tcl_UniCharToUpper) (int ch); /* 323 */
     int (*tcl_UniCharToUtf) (int ch, char *buf); /* 324 */

Index: generic/tclIORChan.c
==================================================================
--- generic/tclIORChan.c
+++ generic/tclIORChan.c
@@ -992,12 +992,12 @@
          * XXX (Delayed postevent executed after channel got removed).
          * XXX Can we detect this ? (check the validity of the owner threadid ?)
          * XXX Actually, in that case the channel should be dead also !
          */
 
-        Tcl_ThreadQueueEvent(rcPtr->owner, (Tcl_Event *) ev, TCL_QUEUE_TAIL);
-        Tcl_ThreadAlert(rcPtr->owner);
+        Tcl_ThreadQueueEvent(rcPtr->owner, (Tcl_Event *) ev,
+		TCL_QUEUE_TAIL|TCL_QUEUE_ALERT_IF_EMPTY);
     }
 #endif
 
     /*
      * Squash interp results left by the event script.
@@ -2996,12 +2996,12 @@
 
     /*
      * Queue the event and poke the other thread's notifier.
      */
 
-    Tcl_ThreadQueueEvent(dst, (Tcl_Event *) evPtr, TCL_QUEUE_TAIL);
-    Tcl_ThreadAlert(dst);
+    Tcl_ThreadQueueEvent(dst, (Tcl_Event *) evPtr,
+	    TCL_QUEUE_TAIL|TCL_QUEUE_ALERT_IF_EMPTY);
 
     /*
      * (*) Block until the handler thread has either processed the transfer or
      * rejected it.
      */

Index: generic/tclIORTrans.c
==================================================================
--- generic/tclIORTrans.c
+++ generic/tclIORTrans.c
@@ -2452,12 +2452,12 @@
 
     /*
      * Queue the event and poke the other thread's notifier.
      */
 
-    Tcl_ThreadQueueEvent(dst, (Tcl_Event *) evPtr, TCL_QUEUE_TAIL);
-    Tcl_ThreadAlert(dst);
+    Tcl_ThreadQueueEvent(dst, (Tcl_Event *) evPtr,
+	    TCL_QUEUE_TAIL|TCL_QUEUE_ALERT_IF_EMPTY);
 
     /*
      * (*) Block until the other thread has either processed the transfer or
      * rejected it.
      */

Index: generic/tclNotify.c
==================================================================
--- generic/tclNotify.c
+++ generic/tclNotify.c
@@ -93,12 +93,12 @@
 
 /*
  * Declarations for routines used only in this file.
  */
 
-static void		QueueEvent(ThreadSpecificData *tsdPtr,
-			    Tcl_Event *evPtr, Tcl_QueuePosition position);
+static int		QueueEvent(ThreadSpecificData *tsdPtr,
+			    Tcl_Event *evPtr, int flags);
 
 /*
  *----------------------------------------------------------------------
  *
  * TclInitNotifier --
@@ -390,16 +390,16 @@
     Tcl_Event *evPtr,		/* Event to add to queue. The storage space
 				 * must have been allocated the caller with
 				 * malloc (ckalloc), and it becomes the
 				 * property of the event queue. It will be
 				 * freed after the event has been handled. */
-    Tcl_QueuePosition position)	/* One of TCL_QUEUE_TAIL, TCL_QUEUE_HEAD,
-				 * TCL_QUEUE_MARK. */
+    int flags)	/* One of TCL_QUEUE_TAIL, TCL_QUEUE_HEAD,
+				 * TCL_QUEUE_MARK, possibly combined with TCL_QUEUE_ALERT_IF_EMPTY. */
 {
     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
 
-    QueueEvent(tsdPtr, evPtr, position);
+    (void) QueueEvent(tsdPtr, evPtr, flags);
 }
 
 /*
  *----------------------------------------------------------------------
  *
@@ -422,12 +422,12 @@
     Tcl_Event *evPtr,		/* Event to add to queue. The storage space
 				 * must have been allocated the caller with
 				 * malloc (ckalloc), and it becomes the
 				 * property of the event queue. It will be
 				 * freed after the event has been handled. */
-    Tcl_QueuePosition position)	/* One of TCL_QUEUE_TAIL, TCL_QUEUE_HEAD,
-				 * TCL_QUEUE_MARK. */
+    int flags)	/* One of TCL_QUEUE_TAIL, TCL_QUEUE_HEAD,
+				 * TCL_QUEUE_MARK, possibly combined with TCL_QUEUE_ALERT_IF_EMPTY. */
 {
     ThreadSpecificData *tsdPtr;
 
     /*
      * Find the notifier associated with the specified thread.
@@ -442,11 +442,13 @@
     /*
      * Queue the event if there was a notifier associated with the thread.
      */
 
     if (tsdPtr) {
-	QueueEvent(tsdPtr, evPtr, position);
+	if (QueueEvent(tsdPtr, evPtr, flags)) {
+	    Tcl_AlertNotifier(tsdPtr->clientData);
+	}
     } else {
 	ckfree(evPtr);
     }
     Tcl_MutexUnlock(&listLock);
 }
@@ -462,54 +464,61 @@
  *	first-out order, but before any events inserted at the tail of the
  *	queue. Events inserted at the head of the queue will be processed in
  *	last-in-first-out order.
  *
  * Results:
- *	None.
+ *	For TCL_QUEUE_ALERT_IF_EMPTY the empty state before the
+ *	operation is returned.
  *
  * Side effects:
  *	None.
  *
  *----------------------------------------------------------------------
  */
 
-static void
+static int
 QueueEvent(
     ThreadSpecificData *tsdPtr,	/* Handle to thread local data that indicates
 				 * which event queue to use. */
     Tcl_Event *evPtr,		/* Event to add to queue.  The storage space
 				 * must have been allocated the caller with
 				 * malloc (ckalloc), and it becomes the
 				 * property of the event queue. It will be
 				 * freed after the event has been handled. */
-    Tcl_QueuePosition position)	/* One of TCL_QUEUE_TAIL, TCL_QUEUE_HEAD,
-				 * TCL_QUEUE_MARK. */
+    int flags)
+				/* One of TCL_QUEUE_TAIL_EX,
+				 * TCL_QUEUE_HEAD_EX, TCL_QUEUE_MARK_EX,
+				 * possibly combined with TCL_QUEUE_ALERT_IF_EMPTY */
 {
+    int wasEmpty = 0;
+
     Tcl_MutexLock(&(tsdPtr->queueMutex));
-    if (position == TCL_QUEUE_TAIL) {
+    if ((flags & 3) == TCL_QUEUE_TAIL) {
 	/*
 	 * Append the event on the end of the queue.
 	 */
 
 	evPtr->nextPtr = NULL;
 	if (tsdPtr->firstEventPtr == NULL) {
 	    tsdPtr->firstEventPtr = evPtr;
+	    wasEmpty = (flags & TCL_QUEUE_ALERT_IF_EMPTY) ? 1 : 0;
 	} else {
 	    tsdPtr->lastEventPtr->nextPtr = evPtr;
 	}
 	tsdPtr->lastEventPtr = evPtr;
-    } else if (position == TCL_QUEUE_HEAD) {
+    } else if ((flags & 3) == TCL_QUEUE_HEAD) {
 	/*
 	 * Push the event on the head of the queue.
 	 */
 
 	evPtr->nextPtr = tsdPtr->firstEventPtr;
 	if (tsdPtr->firstEventPtr == NULL) {
 	    tsdPtr->lastEventPtr = evPtr;
+	    wasEmpty = (flags & TCL_QUEUE_ALERT_IF_EMPTY) ? 1 : 0;
 	}
 	tsdPtr->firstEventPtr = evPtr;
-    } else if (position == TCL_QUEUE_MARK) {
+    } else if ((flags & 3) == TCL_QUEUE_MARK) {
 	/*
 	 * Insert the event after the current marker event and advance the
 	 * marker to the new event.
 	 */
 
@@ -524,10 +533,11 @@
 	if (evPtr->nextPtr == NULL) {
 	    tsdPtr->lastEventPtr = evPtr;
 	}
     }
     Tcl_MutexUnlock(&(tsdPtr->queueMutex));
+    return wasEmpty;
 }
 
 /*
  *----------------------------------------------------------------------
  *

Index: generic/tclTest.c
==================================================================
--- generic/tclTest.c
+++ generic/tclTest.c
@@ -2185,11 +2185,11 @@
     int subCmdIndex;		/* Index of the chosen subcommand */
     static const char *const positions[] = { /* Possible queue positions */
 	"head", "tail", "mark", NULL
     };
     int posIndex;		/* Index of the chosen position */
-    static const Tcl_QueuePosition posNum[] = {
+    static const int posNum[] = {
 				/* Interpretation of the chosen position */
 	TCL_QUEUE_HEAD,
 	TCL_QUEUE_TAIL,
 	TCL_QUEUE_MARK
     };

Index: generic/tclThreadTest.c
==================================================================
--- generic/tclThreadTest.c
+++ generic/tclThreadTest.c
@@ -876,12 +876,11 @@
      * Queue the event and poke the other thread's notifier.
      */
 
     threadEventPtr->event.proc = ThreadEventProc;
     Tcl_ThreadQueueEvent(threadId, (Tcl_Event *) threadEventPtr,
-	    TCL_QUEUE_TAIL);
-    Tcl_ThreadAlert(threadId);
+	    TCL_QUEUE_TAIL|TCL_QUEUE_ALERT_IF_EMPTY);
 
     if (!wait) {
 	Tcl_MutexUnlock(&threadMutex);
 	return TCL_OK;
     }