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johnny - That actually helps a lot and fairly clearly indicates 
the source of this hanging problem.  To give more context to 
that area, this is in the final shutdown code where it is 
(obviously) shutting down the console I/O.  The reader is 
shutdown without a check for more input (why, we are 
exiting?), so there is no issue there.

The writer however wants to make sure that the console 
output channel is drained before exit.  A blocking channel 
that is not being flushed will cause a hang.

So the question is, what is the stdio setup for Tcl in 
Py/Tkinter?  That should be examined to see whether stdio is 
clear to flush on exit.

Perhaps you can also help with more debugging.  Could you 
wrap the problematic WaitForSingleObject call with
if (consolePtr->toWrite) { ...
and perhaps also print out what to write.  It may be that 
blocking output isn't the problem at all, but rather that we are 
never receiving the signal on consolePtr->writable (usually 
done in the writer thread).  The consolePtr->toWrite check 
will at least ensure flushed channels do not enter this 
potential hanging state.