Yielding event loop

["Mark Tilford" <ralphmerridew gmail com>]

I hope this isn't too unclear:

For various reasons, one handler needs to do something moderately
complex, and partway through, I need to get input from another widget.
The stack frame is involved enough that I can't easily return; I want
the program to be portable (and I'd prefer to avoid trying to
synchronize threads if possible).

Is it possible to have the handler simply transfer control back to the
main event loop until the other widget sends its message?