#2960 Endless loop inside Tk library

[Gregor Cramer]

I have the following case:
1. Mapping a modal window (with local grab)
2. Mapping a subwindow of the modal window
3. Mouse click into the subwindow
The result is a frozen screen. With debugging I discovered that an endless call of function TkPointerEvent() is freezing the screen. I made a patch to this function (see attached file; possibly a better patch is required) and my application is working. Unfortunately I couldn't build a simple test application with the same behavior.

[Gregor Cramer]

Patch of function TkPointerEvent()

[Steven]

I suppose the "subwindow of the modal window" is a toplevel ?
In this case, it sounds like a bug, but i wonder if you're abusing grab. Grab's man page says to use with care.

This is your diff

--- /root/1 2012-05-23 20:16:39.000000000 +0000
+++ /root/new/TkPointerEvent.patch.c 2012-05-23 20:12:42.000000000 +0000
@@ -192,7 +192,17 @@
}
}
if (winPtr2 != winPtr) {
+/********** FIX of endless loop *********************************/
+ if (eventPtr->xbutton.send_event == True) {
+ /* already redirected */
+ return 1;
+ }
+/********** END fix of endless loop *****************************/
TkChangeEventWindow(eventPtr, winPtr2);
+/********** FIX of endless loop *********************************/
+ /* mark as redirected to avoid endless calls of this function */
+ eventPtr->xbutton.send_event = True;
+/********** END fix of endless loop *****************************/
Tk_QueueWindowEvent(eventPtr, TCL_QUEUE_HEAD);
return 0; /* Note 3. */
}

[Gregor Cramer]

> I suppose the "subwindow of the modal window" is a toplevel ?
Yes.

> but i wonder if you're abusing grab. Grab's man page says to use with care.
I don not abuse grabs, the file selection dialog (the parent toplevel) has to be modal (local modality), and the child toplevel is the help dialog.