Tkinter wait_variable hang on exit SOLVED
Russell E. Owen
rowen at cesmail.net
Wed Jun 23 23:56:42 CEST 2004
In article <ca550b$9n7$07$1 at news.t-online.com>,
Peter Otten <__peter__ at web.de> wrote:
><veröffentlicht & per Mail versendet>
>Russell E. Owen wrote:
>> I want to support execution of simple user-written scripts in a Tkinter
>> application. The scripts should be able to wait for data and such
>> without hanging the GUI (and without having to write the script as a
>> bunch of asynchronously called subroutines).
>> I decided to use Tkinter's wait_variable. I built a "script runner"
>> object that has suitable wait methods...
>> Unfortunately, if a user closes the root window while wait_variable is
>> waiting, the application never fully quits. On my unix box the root
>> window closes but the command-line prompt never returns and ^C is
>> ignored. The process isn't using excess cpu cycles; it's just not
>Without any deeper insight in your script - could the following meet your
> # instead of atexit.register():
> def dw():
> self._tk.protocol("WM_DELETE_WINDOW", dw)
>and further down:
> root = Tkinter.Tk()
> ScriptRunner._tk = root
>That way your runner would get notified if the window shall be closed.
This fix does, indeed work! Also, there is an even easier solution: it
turns out to be sufficient to bind to <Destroy>. The callback sets the
variable being waited on and the application no longer hangs.
However, wait_variable proved to unsuitable because if multiple users
use wait_variable, they stack up. If a new routine executes
wait_variable while an existing one is waiting, the new routine has to
fully finish executing before the first one resumes. This is
understandable in hindsight, but disappointing. As a result:
- only one script could be run at a time
- if wait_variable is used elsewhere (and some dialog boxes are reported
to do so) then that would also pause an executing script
I ended up implementing user-written scripts as generators, instead. The
user's script ends up looking like this:
where sr is a ScriptRunner object. sr's doCmd, waitMS etc. set up a
termination condition that causes the script generator's next() method
to be executed, until the script is finished.
This works fully normally with Tk's event loop. No wait_variable magic
is involved and multiple scripts can peacefully run at the same time.
The big problem is that users are likely to forget the "yield"
statement. To help with this I increment one counter each time a wait
subroutine begins and another counter each time the script generator is
executed. Any discrepancy indicates a missing yield.
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