tkinter and threading

Are Tkinter callbacks run in separate threads?  Do I need to use threading locks to protect data shared
between callbacks that can run at the same time? I'm running Python 2.3 and Tkinter on Windows.

I have two callbacks: cb_close and cb_run.  cb_close cleans up, then uses Tkinter.Toplevel.destroy; it is
bound to WM_DELETE_WINDOW via Tkinter.Toplevel.protocol.

cb_run uses a COM component to perform a lengthy operation.  The COM component calls back to the Python world
often enough that I can keep my GUI responsive using Tkinter.Toplevel.update.

Bad things happen if I allow cb_close to call destroy while cb_run is in progress: cb_run eventually asks
the Tkinter world to post a completion dialog.  To keep this from happening I use a state variable to tell
cb_close that it should not call destroy if cb_run is in progress and to tell cb_run that it should not
execute if a cb_close is in progress.

I can definitely get cb_close to run at the same time as cb_run, which suggests that the Tkinter eventloop
executes its callbacks in separate threads.  All this lead me to use a lock to protect read/write of the
state variable.  Was this necessary?  Is there something in the way that Tkinter handles callbacks that
automatically protects shared data structures?

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Greg Lee / Pharsight Corporation / Suite 200
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