Add an optional hack for threads in Tkinter.

This one works!  However it requires using a modified version of
tclNotify.c (provided), which requires access to the Tcl source
to compile it.  In order to enable this hack, add the following
to the Setup line for _tkinter:
   tclNotify.c -DHAVE_PYTCL_WAITUNTILEVENT -I$(TCL)/generic
where TCL points to the source tree of Tcl 8.0.  Other versions
of Tcl are not supported.

The tclNotify.c file is copyrighted by Sun Microsystems; the
licensing terms are in the file license.terms.  According to this
file, no further permission to distribute this is required,
provided the file license.terms is included.  Hence, I am checking
that in, too.

3 files changed, 1005 insertions, 2 deletions

diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index 04150d1..1307053 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -1265,7 +1265,7 @@ Tkapp_MainLoop(self, args)
 	       !errorInCmd)
 	{
 		int result;
-#ifdef THIS_CODE_IS_BUGGY
+#ifdef HAVE_PYTCL_WAITUNTILEVENT
 		result = Tcl_DoOneEvent(TCL_DONT_WAIT);
 		if (PyErr_CheckSignals() != 0)
 			return NULL;
@@ -1275,7 +1275,7 @@ Tkapp_MainLoop(self, args)
 		   thread-safe, but it seems *rather* safe as long as
 		   no two threads call mainloop() simultaneously. */
 		Py_BEGIN_ALLOW_THREADS
-		result = Tcl_WaitForEvent((Tcl_Time *)NULL);
+		result = PyTcl_WaitUntilEvent();
 		Py_END_ALLOW_THREADS
 #else
 		result = Tcl_DoOneEvent(0);
diff --git a/Modules/license.terms b/Modules/license.terms
new file mode 100644
index 0000000..96ad966
--- /dev/null
+++ b/Modules/license.terms
@@ -0,0 +1,39 @@
+This software is copyrighted by the Regents of the University of
+California, Sun Microsystems, Inc., and other parties.  The following
+terms apply to all files associated with the software unless explicitly
+disclaimed in individual files.
+
+The authors hereby grant permission to use, copy, modify, distribute,
+and license this software and its documentation for any purpose, provided
+that existing copyright notices are retained in all copies and that this
+notice is included verbatim in any distributions. No written agreement,
+license, or royalty fee is required for any of the authorized uses.
+Modifications to this software may be copyrighted by their authors
+and need not follow the licensing terms described here, provided that
+the new terms are clearly indicated on the first page of each file where
+they apply.
+
+IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
+FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
+DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+
+THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
+INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE
+IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
+NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
+MODIFICATIONS.
+
+GOVERNMENT USE: If you are acquiring this software on behalf of the
+U.S. government, the Government shall have only "Restricted Rights"
+in the software and related documentation as defined in the Federal 
+Acquisition Regulations (FARs) in Clause 52.227.19 (c) (2).  If you
+are acquiring the software on behalf of the Department of Defense, the
+software shall be classified as "Commercial Computer Software" and the
+Government shall have only "Restricted Rights" as defined in Clause
+252.227-7013 (c) (1) of DFARs.  Notwithstanding the foregoing, the
+authors grant the U.S. Government and others acting in its behalf
+permission to use and distribute the software in accordance with the
+terms specified in this license. 
diff --git a/Modules/tclNotify.c b/Modules/tclNotify.c
new file mode 100644
index 0000000..429416e
--- /dev/null
+++ b/Modules/tclNotify.c
@@ -0,0 +1,964 @@
+/*
+ * This is a modified version of tclNotify.c from Sun's Tcl 8.0
+ * distribution.  The purpose of the modification is to provide an
+ * interface to the internals of the notifier that make it possible to
+ * write safe multi-threaded Python programs that use Tkinter.
+ *
+ * Original comments follow.  The file license.terms from the Tcl 8.0
+ * distribution is contained in this directory, as required.
+ */
+
+/* 
+ * tclNotify.c --
+ *
+ *	This file implements the generic portion of the Tcl notifier.
+ *	The notifier is lowest-level part of the event system.  It
+ *	manages an event queue that holds Tcl_Event structures.  The
+ *	platform specific portion of the notifier is defined in the
+ *	tcl*Notify.c files in each platform directory.
+ *
+ * Copyright (c) 1995-1997 Sun Microsystems, Inc.
+ *
+ * See the file "license.terms" for information on usage and redistribution
+ * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+ *
+ * SCCS: @(#) tclNotify.c 1.15 97/06/18 17:14:04
+ */
+
+#include "tclInt.h"
+#include "tclPort.h"
+
+/*
+ * The following static indicates whether this module has been initialized.
+ */
+
+static int initialized = 0;
+
+/*
+ * For each event source (created with Tcl_CreateEventSource) there
+ * is a structure of the following type:
+ */
+
+typedef struct EventSource {
+    Tcl_EventSetupProc *setupProc;
+    Tcl_EventCheckProc *checkProc;
+    ClientData clientData;
+    struct EventSource *nextPtr;
+} EventSource;
+
+/*
+ * The following structure keeps track of the state of the notifier.
+ * The first three elements keep track of the event queue.  In addition to
+ * the first (next to be serviced) and last events in the queue, we keep
+ * track of a "marker" event.  This provides a simple priority mechanism
+ * whereby events can be inserted at the front of the queue but behind all
+ * other high-priority events already in the queue (this is used for things
+ * like a sequence of Enter and Leave events generated during a grab in
+ * Tk).
+ */
+
+static struct {
+    Tcl_Event *firstEventPtr;	/* First pending event, or NULL if none. */
+    Tcl_Event *lastEventPtr;	/* Last pending event, or NULL if none. */
+    Tcl_Event *markerEventPtr;	/* Last high-priority event in queue, or
+				 * NULL if none. */
+    int serviceMode;		/* One of TCL_SERVICE_NONE or
+				 * TCL_SERVICE_ALL. */
+    int blockTimeSet;		/* 0 means there is no maximum block
+				 * time:  block forever. */
+    Tcl_Time blockTime;		/* If blockTimeSet is 1, gives the
+				 * maximum elapsed time for the next block. */
+    int inTraversal;		/* 1 if Tcl_SetMaxBlockTime is being
+				 * called during an event source traversal. */
+    EventSource *firstEventSourcePtr;
+				/* Pointer to first event source in
+				 * global list of event sources. */
+} notifier;
+
+/*
+ * Declarations for functions used in this file.
+ */
+
+static void	InitNotifier _ANSI_ARGS_((void));
+static void	NotifierExitHandler _ANSI_ARGS_((ClientData clientData));
+
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * InitNotifier --
+ *
+ *	This routine is called to initialize the notifier module.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Creates an exit handler and initializes static data.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+InitNotifier()
+{
+    initialized = 1;
+    memset(&notifier, 0, sizeof(notifier));
+    notifier.serviceMode = TCL_SERVICE_NONE;
+    Tcl_CreateExitHandler(NotifierExitHandler, NULL);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * NotifierExitHandler --
+ *
+ *	This routine is called during Tcl finalization.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Clears the notifier intialization flag.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+NotifierExitHandler(clientData)
+    ClientData clientData;  /* Not used. */
+{
+    initialized = 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_CreateEventSource --
+ *
+ *	This procedure is invoked to create a new source of events.
+ *	The source is identified by a procedure that gets invoked
+ *	during Tcl_DoOneEvent to check for events on that source
+ *	and queue them.
+ *
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	SetupProc and checkProc will be invoked each time that Tcl_DoOneEvent
+ *	runs out of things to do.  SetupProc will be invoked before
+ *	Tcl_DoOneEvent calls select or whatever else it uses to wait
+ *	for events.  SetupProc typically calls functions like Tcl_WatchFile
+ *	or Tcl_SetMaxBlockTime to indicate what to wait for.
+ *
+ *	CheckProc is called after select or whatever operation was actually
+ *	used to wait.  It figures out whether anything interesting actually
+ *	happened (e.g. by calling Tcl_FileReady), and then calls
+ *	Tcl_QueueEvent to queue any events that are ready.
+ *
+ *	Each of these procedures is passed two arguments, e.g.
+ *		(*checkProc)(ClientData clientData, int flags));
+ *	ClientData is the same as the clientData argument here, and flags
+ *	is a combination of things like TCL_FILE_EVENTS that indicates
+ *	what events are of interest:  setupProc and checkProc use flags
+ *	to figure out whether their events are relevant or not.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+Tcl_CreateEventSource(setupProc, checkProc, clientData)
+    Tcl_EventSetupProc *setupProc;	/* Procedure to invoke to figure out
+					 * what to wait for. */
+    Tcl_EventCheckProc *checkProc;	/* Procedure to call after waiting
+					 * to see what happened. */
+    ClientData clientData;		/* One-word argument to pass to
+					 * setupProc and checkProc. */
+{
+    EventSource *sourcePtr;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    sourcePtr = (EventSource *) ckalloc(sizeof(EventSource));
+    sourcePtr->setupProc = setupProc;
+    sourcePtr->checkProc = checkProc;
+    sourcePtr->clientData = clientData;
+    sourcePtr->nextPtr = notifier.firstEventSourcePtr;
+    notifier.firstEventSourcePtr = sourcePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_DeleteEventSource --
+ *
+ *	This procedure is invoked to delete the source of events
+ *	given by proc and clientData.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The given event source is cancelled, so its procedure will
+ *	never again be called.  If no such source exists, nothing
+ *	happens.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+Tcl_DeleteEventSource(setupProc, checkProc, clientData)
+    Tcl_EventSetupProc *setupProc;	/* Procedure to invoke to figure out
+					 * what to wait for. */
+    Tcl_EventCheckProc *checkProc;	/* Procedure to call after waiting
+					 * to see what happened. */
+    ClientData clientData;		/* One-word argument to pass to
+					 * setupProc and checkProc. */
+{
+    EventSource *sourcePtr, *prevPtr;
+
+    for (sourcePtr = notifier.firstEventSourcePtr, prevPtr = NULL;
+	    sourcePtr != NULL;
+	    prevPtr = sourcePtr, sourcePtr = sourcePtr->nextPtr) {
+	if ((sourcePtr->setupProc != setupProc)
+		|| (sourcePtr->checkProc != checkProc)
+		|| (sourcePtr->clientData != clientData)) {
+	    continue;
+	}
+	if (prevPtr == NULL) {
+	    notifier.firstEventSourcePtr = sourcePtr->nextPtr;
+	} else {
+	    prevPtr->nextPtr = sourcePtr->nextPtr;
+	}
+	ckfree((char *) sourcePtr);
+	return;
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_QueueEvent --
+ *
+ *	Insert an event into the Tk event queue at one of three
+ *	positions: the head, the tail, or before a floating marker.
+ *	Events inserted before the marker will be processed in
+ *	first-in-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.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+Tcl_QueueEvent(evPtr, position)
+    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. */
+{
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    if (position == TCL_QUEUE_TAIL) {
+	/*
+	 * Append the event on the end of the queue.
+	 */
+
+	evPtr->nextPtr = NULL;
+	if (notifier.firstEventPtr == NULL) {
+	    notifier.firstEventPtr = evPtr;
+	} else {
+	    notifier.lastEventPtr->nextPtr = evPtr;
+	}
+	notifier.lastEventPtr = evPtr;
+    } else if (position == TCL_QUEUE_HEAD) {
+	/*
+	 * Push the event on the head of the queue.
+	 */
+
+	evPtr->nextPtr = notifier.firstEventPtr;
+	if (notifier.firstEventPtr == NULL) {
+	    notifier.lastEventPtr = evPtr;
+	}	    
+	notifier.firstEventPtr = evPtr;
+    } else if (position == TCL_QUEUE_MARK) {
+	/*
+	 * Insert the event after the current marker event and advance
+	 * the marker to the new event.
+	 */
+
+	if (notifier.markerEventPtr == NULL) {
+	    evPtr->nextPtr = notifier.firstEventPtr;
+	    notifier.firstEventPtr = evPtr;
+	} else {
+	    evPtr->nextPtr = notifier.markerEventPtr->nextPtr;
+	    notifier.markerEventPtr->nextPtr = evPtr;
+	}
+	notifier.markerEventPtr = evPtr;
+	if (evPtr->nextPtr == NULL) {
+	    notifier.lastEventPtr = evPtr;
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_DeleteEvents --
+ *
+ *	Calls a procedure for each event in the queue and deletes those
+ *	for which the procedure returns 1. Events for which the
+ *	procedure returns 0 are left in the queue.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Potentially removes one or more events from the event queue.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+Tcl_DeleteEvents(proc, clientData)
+    Tcl_EventDeleteProc *proc;		/* The procedure to call. */
+    ClientData clientData;    		/* type-specific data. */
+{
+    Tcl_Event *evPtr, *prevPtr, *hold;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    for (prevPtr = (Tcl_Event *) NULL, evPtr = notifier.firstEventPtr;
+             evPtr != (Tcl_Event *) NULL;
+             ) {
+        if ((*proc) (evPtr, clientData) == 1) {
+            if (notifier.firstEventPtr == evPtr) {
+                notifier.firstEventPtr = evPtr->nextPtr;
+                if (evPtr->nextPtr == (Tcl_Event *) NULL) {
+                    notifier.lastEventPtr = (Tcl_Event *) NULL;
+                }
+            } else {
+                prevPtr->nextPtr = evPtr->nextPtr;
+            }
+            hold = evPtr;
+            evPtr = evPtr->nextPtr;
+            ckfree((char *) hold);
+        } else {
+            prevPtr = evPtr;
+            evPtr = evPtr->nextPtr;
+        }
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_ServiceEvent --
+ *
+ *	Process one event from the event queue, or invoke an
+ *	asynchronous event handler.
+ *
+ * Results:
+ *	The return value is 1 if the procedure actually found an event
+ *	to process.  If no processing occurred, then 0 is returned.
+ *
+ * Side effects:
+ *	Invokes all of the event handlers for the highest priority
+ *	event in the event queue.  May collapse some events into a
+ *	single event or discard stale events.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_ServiceEvent(flags)
+    int flags;			/* Indicates what events should be processed.
+				 * May be any combination of TCL_WINDOW_EVENTS
+				 * TCL_FILE_EVENTS, TCL_TIMER_EVENTS, or other
+				 * flags defined elsewhere.  Events not
+				 * matching this will be skipped for processing
+				 * later. */
+{
+    Tcl_Event *evPtr, *prevPtr;
+    Tcl_EventProc *proc;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    /*
+     * Asynchronous event handlers are considered to be the highest
+     * priority events, and so must be invoked before we process events
+     * on the event queue.
+     */
+    
+    if (Tcl_AsyncReady()) {
+	(void) Tcl_AsyncInvoke((Tcl_Interp *) NULL, 0);
+	return 1;
+    }
+
+    /*
+     * No event flags is equivalent to TCL_ALL_EVENTS.
+     */
+    
+    if ((flags & TCL_ALL_EVENTS) == 0) {
+	flags |= TCL_ALL_EVENTS;
+    }
+
+    /*
+     * Loop through all the events in the queue until we find one
+     * that can actually be handled.
+     */
+
+    for (evPtr = notifier.firstEventPtr; evPtr != NULL;
+	 evPtr = evPtr->nextPtr) {
+	/*
+	 * Call the handler for the event.  If it actually handles the
+	 * event then free the storage for the event.  There are two
+	 * tricky things here, but stemming from the fact that the event
+	 * code may be re-entered while servicing the event:
+	 *
+	 * 1. Set the "proc" field to NULL.  This is a signal to ourselves
+	 *    that we shouldn't reexecute the handler if the event loop
+	 *    is re-entered.
+	 * 2. When freeing the event, must search the queue again from the
+	 *    front to find it.  This is because the event queue could
+	 *    change almost arbitrarily while handling the event, so we
+	 *    can't depend on pointers found now still being valid when
+	 *    the handler returns.
+	 */
+
+	proc = evPtr->proc;
+	evPtr->proc = NULL;
+	if ((proc != NULL) && (*proc)(evPtr, flags)) {
+	    if (notifier.firstEventPtr == evPtr) {
+		notifier.firstEventPtr = evPtr->nextPtr;
+		if (evPtr->nextPtr == NULL) {
+		    notifier.lastEventPtr = NULL;
+		}
+		if (notifier.markerEventPtr == evPtr) {
+		    notifier.markerEventPtr = NULL;
+		}
+	    } else {
+		for (prevPtr = notifier.firstEventPtr;
+		     prevPtr->nextPtr != evPtr; prevPtr = prevPtr->nextPtr) {
+		    /* Empty loop body. */
+		}
+		prevPtr->nextPtr = evPtr->nextPtr;
+		if (evPtr->nextPtr == NULL) {
+		    notifier.lastEventPtr = prevPtr;
+		}
+		if (notifier.markerEventPtr == evPtr) {
+		    notifier.markerEventPtr = prevPtr;
+		}
+	    }
+	    ckfree((char *) evPtr);
+	    return 1;
+	} else {
+	    /*
+	     * The event wasn't actually handled, so we have to restore
+	     * the proc field to allow the event to be attempted again.
+	     */
+
+	    evPtr->proc = proc;
+	}
+
+	/*
+	 * The handler for this event asked to defer it.  Just go on to
+	 * the next event.
+	 */
+
+	continue;
+    }
+    return 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_GetServiceMode --
+ *
+ *	This routine returns the current service mode of the notifier.
+ *
+ * Results:
+ *	Returns either TCL_SERVICE_ALL or TCL_SERVICE_NONE.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_GetServiceMode()
+{
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    return notifier.serviceMode;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_SetServiceMode --
+ *
+ *	This routine sets the current service mode of the notifier.
+ *
+ * Results:
+ *	Returns the previous service mode.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_SetServiceMode(mode)
+    int mode;			/* New service mode: TCL_SERVICE_ALL or
+				 * TCL_SERVICE_NONE */
+{
+    int oldMode;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    oldMode = notifier.serviceMode;
+    notifier.serviceMode = mode;
+    return oldMode;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_SetMaxBlockTime --
+ *
+ *	This procedure is invoked by event sources to tell the notifier
+ *	how long it may block the next time it blocks.  The timePtr
+ *	argument gives a maximum time;  the actual time may be less if
+ *	some other event source requested a smaller time.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	May reduce the length of the next sleep in the notifier.
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+Tcl_SetMaxBlockTime(timePtr)
+    Tcl_Time *timePtr;		/* Specifies a maximum elapsed time for
+				 * the next blocking operation in the
+				 * event notifier. */
+{
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    if (!notifier.blockTimeSet || (timePtr->sec < notifier.blockTime.sec)
+	    || ((timePtr->sec == notifier.blockTime.sec)
+	    && (timePtr->usec < notifier.blockTime.usec))) {
+	notifier.blockTime = *timePtr;
+	notifier.blockTimeSet = 1;
+    }
+
+    /*
+     * If we are called outside an event source traversal, set the
+     * timeout immediately.
+     */
+
+    if (!notifier.inTraversal) {
+	if (notifier.blockTimeSet) {
+	    Tcl_SetTimer(&notifier.blockTime);
+	} else {
+	    Tcl_SetTimer(NULL);
+	}
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_DoOneEvent --
+ *
+ *	Process a single event of some sort.  If there's no work to
+ *	do, wait for an event to occur, then process it.
+ *
+ * Results:
+ *	The return value is 1 if the procedure actually found an event
+ *	to process.  If no processing occurred, then 0 is returned (this
+ *	can happen if the TCL_DONT_WAIT flag is set or if there are no
+ *	event handlers to wait for in the set specified by flags).
+ *
+ * Side effects:
+ *	May delay execution of process while waiting for an event,
+ *	unless TCL_DONT_WAIT is set in the flags argument.  Event
+ *	sources are invoked to check for and queue events.  Event
+ *	handlers may produce arbitrary side effects.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_DoOneEvent(flags)
+    int flags;			/* Miscellaneous flag values:  may be any
+				 * combination of TCL_DONT_WAIT,
+				 * TCL_WINDOW_EVENTS, TCL_FILE_EVENTS,
+				 * TCL_TIMER_EVENTS, TCL_IDLE_EVENTS, or
+				 * others defined by event sources. */
+{
+    int result = 0, oldMode;
+    EventSource *sourcePtr;
+    Tcl_Time *timePtr;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    /*
+     * The first thing we do is to service any asynchronous event
+     * handlers.
+     */
+    
+    if (Tcl_AsyncReady()) {
+	(void) Tcl_AsyncInvoke((Tcl_Interp *) NULL, 0);
+	return 1;
+    }
+
+    /*
+     * No event flags is equivalent to TCL_ALL_EVENTS.
+     */
+    
+    if ((flags & TCL_ALL_EVENTS) == 0) {
+	flags |= TCL_ALL_EVENTS;
+    }
+
+    /*
+     * Set the service mode to none so notifier event routines won't
+     * try to service events recursively.
+     */
+
+    oldMode = notifier.serviceMode;
+    notifier.serviceMode = TCL_SERVICE_NONE;
+
+    /*
+     * The core of this procedure is an infinite loop, even though
+     * we only service one event.  The reason for this is that we
+     * may be processing events that don't do anything inside of Tcl.
+     */
+
+    while (1) {
+
+	/*
+	 * If idle events are the only things to service, skip the
+	 * main part of the loop and go directly to handle idle
+	 * events (i.e. don't wait even if TCL_DONT_WAIT isn't set).
+	 */
+
+	if ((flags & TCL_ALL_EVENTS) == TCL_IDLE_EVENTS) {
+	    flags = TCL_IDLE_EVENTS|TCL_DONT_WAIT;
+	    goto idleEvents;
+	}
+
+	/*
+	 * Ask Tcl to service a queued event, if there are any.
+	 */
+
+	if (Tcl_ServiceEvent(flags)) {
+	    result = 1;	    
+	    break;
+	}
+
+	/*
+	 * If TCL_DONT_WAIT is set, be sure to poll rather than
+	 * blocking, otherwise reset the block time to infinity.
+	 */
+
+	if (flags & TCL_DONT_WAIT) {
+	    notifier.blockTime.sec = 0;
+	    notifier.blockTime.usec = 0;
+	    notifier.blockTimeSet = 1;
+	} else {
+	    notifier.blockTimeSet = 0;
+	}
+
+	/*
+	 * Set up all the event sources for new events.  This will
+	 * cause the block time to be updated if necessary.
+	 */
+
+	notifier.inTraversal = 1;
+	for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	     sourcePtr = sourcePtr->nextPtr) {
+	    if (sourcePtr->setupProc) {
+		(sourcePtr->setupProc)(sourcePtr->clientData, flags);
+	    }
+	}
+	notifier.inTraversal = 0;
+
+	if ((flags & TCL_DONT_WAIT) || notifier.blockTimeSet) {
+	    timePtr = &notifier.blockTime;
+	} else {
+	    timePtr = NULL;
+	}
+
+	/*
+	 * Wait for a new event or a timeout.  If Tcl_WaitForEvent
+	 * returns -1, we should abort Tcl_DoOneEvent.
+	 */
+
+	result = Tcl_WaitForEvent(timePtr);
+	if (result < 0) {
+	    result = 0;
+	    break;
+	}
+
+	/*
+	 * Check all the event sources for new events.
+	 */
+
+	for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	     sourcePtr = sourcePtr->nextPtr) {
+	    if (sourcePtr->checkProc) {
+		(sourcePtr->checkProc)(sourcePtr->clientData, flags);
+	    }
+	}
+
+	/*
+	 * Check for events queued by the notifier or event sources.
+	 */
+
+	if (Tcl_ServiceEvent(flags)) {
+	    result = 1;
+	    break;
+	}
+
+	/*
+	 * We've tried everything at this point, but nobody we know
+	 * about had anything to do.  Check for idle events.  If none,
+	 * either quit or go back to the top and try again.
+	 */
+
+	idleEvents:
+	if (flags & TCL_IDLE_EVENTS) {
+	    if (TclServiceIdle()) {
+		result = 1;
+		break;
+	    }
+	}
+	if (flags & TCL_DONT_WAIT) {
+	    break;
+	}
+    }
+
+    notifier.serviceMode = oldMode;
+    return result;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_ServiceAll --
+ *
+ *	This routine checks all of the event sources, processes
+ *	events that are on the Tcl event queue, and then calls the
+ *	any idle handlers.  Platform specific notifier callbacks that
+ *	generate events should call this routine before returning to
+ *	the system in order to ensure that Tcl gets a chance to
+ *	process the new events.
+ *
+ * Results:
+ *	Returns 1 if an event or idle handler was invoked, else 0.
+ *
+ * Side effects:
+ *	Anything that an event or idle handler may do.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_ServiceAll()
+{
+    int result = 0;
+    EventSource *sourcePtr;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    if (notifier.serviceMode == TCL_SERVICE_NONE) {
+	return result;
+    }
+
+    /*
+     * We need to turn off event servicing like we to in Tcl_DoOneEvent,
+     * to avoid recursive calls.
+     */
+    
+    notifier.serviceMode = TCL_SERVICE_NONE;
+
+    /*
+     * Check async handlers first.
+     */
+
+    if (Tcl_AsyncReady()) {
+	(void) Tcl_AsyncInvoke((Tcl_Interp *) NULL, 0);
+    }
+
+    /*
+     * Make a single pass through all event sources, queued events,
+     * and idle handlers.  Note that we wait to update the notifier
+     * timer until the end so we can avoid multiple changes.
+     */
+
+    notifier.inTraversal = 1;
+    notifier.blockTimeSet = 0;
+
+    for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	 sourcePtr = sourcePtr->nextPtr) {
+	if (sourcePtr->setupProc) {
+	    (sourcePtr->setupProc)(sourcePtr->clientData, TCL_ALL_EVENTS);
+	}
+    }
+    for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	 sourcePtr = sourcePtr->nextPtr) {
+	if (sourcePtr->checkProc) {
+	    (sourcePtr->checkProc)(sourcePtr->clientData, TCL_ALL_EVENTS);
+	}
+    }
+
+    while (Tcl_ServiceEvent(0)) {
+	result = 1;
+    }
+    if (TclServiceIdle()) {
+	result = 1;
+    }
+
+    if (!notifier.blockTimeSet) {
+	Tcl_SetTimer(NULL);
+    } else {
+	Tcl_SetTimer(&notifier.blockTime);
+    }
+    notifier.inTraversal = 0;
+    notifier.serviceMode = TCL_SERVICE_ALL;
+    return result;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * PyTcl_WaitUntilEvent --
+ *
+ *	New function to wait until a Tcl event is ready without
+ *	actually handling the event.  This is different than
+ *	TclWaitForEvent(): that function doesn't call the event
+ *	check routines, which is necessary for our purpose.
+ *	We also can't use Tcl_DoOneEvent(TCL_DONT_WAIT), since that
+ *	does too much: it handles the event.  We want the *handling*
+ *	of the event to be done with the Python lock held, but the
+ *	*waiting* with the lock released.
+ *
+ *	Since the event administration is not exported, our only
+ *	choice is to use a modified copy of the file tclNotify.c,
+ *	containing this additional function that makes the desired
+ *	functionality available.  It is mostly a stripped down version
+ *	of the code in Tcl_DoOneEvent().
+ *
+ *	This requires that you link with a static version of the Tcl
+ *	library.  On Windows/Mac, a custom compilation of Tcl may be
+ *	required (I haven't tried this yet).
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+PyTcl_WaitUntilEvent()
+{
+    int flags = TCL_ALL_EVENTS;
+    int result = 0, oldMode;
+    EventSource *sourcePtr;
+    Tcl_Time *timePtr;
+
+    if (!initialized) {
+	InitNotifier();
+    }
+
+    /*
+     * The first thing we do is to service any asynchronous event
+     * handlers.
+     */
+    
+    if (Tcl_AsyncReady())
+	return 1;
+
+    /*
+     * Set the service mode to none so notifier event routines won't
+     * try to service events recursively.
+     */
+
+    oldMode = notifier.serviceMode;
+    notifier.serviceMode = TCL_SERVICE_NONE;
+
+    notifier.blockTimeSet = 0;
+
+    /*
+     * Set up all the event sources for new events.  This will
+     * cause the block time to be updated if necessary.
+     */
+
+    notifier.inTraversal = 1;
+    for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	 sourcePtr = sourcePtr->nextPtr) {
+	if (sourcePtr->setupProc) {
+	    (sourcePtr->setupProc)(sourcePtr->clientData, flags);
+	}
+    }
+    notifier.inTraversal = 0;
+
+    timePtr = NULL;
+
+    /*
+     * Wait for a new event or a timeout.  If Tcl_WaitForEvent
+     * returns -1, we should abort Tcl_DoOneEvent.
+     */
+
+    result = Tcl_WaitForEvent(timePtr);
+    if (result < 0)
+	return 0;
+
+    /*
+     * Check all the event sources for new events.
+     */
+
+    for (sourcePtr = notifier.firstEventSourcePtr; sourcePtr != NULL;
+	 sourcePtr = sourcePtr->nextPtr) {
+	if (sourcePtr->checkProc) {
+	    (sourcePtr->checkProc)(sourcePtr->clientData, flags);
+	}
+    }
+
+    notifier.serviceMode = oldMode;
+    return result;
+}