Tkinter long-running window freezes
John O'Hagan
research at johnohagan.com
Fri Feb 26 18:59:24 EST 2021
On Fri, 26 Feb 2021 08:19:14 +0100
Christian Gollwitzer <auriocus at gmx.de> wrote:
> Am 26.02.21 um 06:15 schrieb John O'Hagan:
[...]
> >
> > I've followed your suggestions as per my last post, and can confirm
> > the same freezing behaviour when running your code directly as a
> > tclsh script on Debian Testing, Tcl 8.6.11.
>
> You might report this as a bug to the Tcl bugtracker
> https://core.tcl-lang.org/tk/ticket
>
> I guess the problem is with the steady creation of widgets. Tk was
> not meant to be used like that. Tkinter creates new widget names for
> each widget with random numbers, just like the Tcl code above does,
> whereas in a usual Tcl/Tk program the names are given by the
> programmer.
Thanks, I will make the bug report. However, based on your comments
above, it looks similar to this one, closed as invalid 16 years ago:
https://core.tcl-lang.org/tk/tktview/1173484fffffffffffff
This was also related to memory "creep" caused by Tk's cache of names,
which AIUI is a Tk design feature (but I don't know Tk!).
> Can you also check this program, which reuses the same widget path
> name, albeit does the creation/destruction in cycles:
>
> ======================
> package require Tk
>
> proc randint {} {
> expr {int(rand()*10000000)}
> }
>
> proc display {label} {
> destroy $label
> set label [label .l -text [randint]]
> pack $label
> after 100 [list display $label]
> }
>
> display [label .l]
> ========================
>
I have tried this overnight and it is still running, not frozen and with
no apparent increase in memory use. I guess that is likely the issue. I
don't know Tcl/Tk - is there a way to emulate the above approach of
re-using the widget name in tkinter?
> As mentioned by others, typically you wouldn't continuously recreate
> new widgets, but either update the text of the widget
> (label['text']="New text") or attaching a StringVar() )
>
> or, if you must rearrange the widgets, you pack_forget() them and
> then repack them.
>
> Christian
This is possible of course, but will require more than a repack. In my
use case, each widget is an attribute of a Python object, intended
control and display data about that object, and there is an
indeterminate number of such objects at any given time. I had
assumed I could just destroy the widget and let the object go out of
scope to be garbage collected. I'll need to redesign this altogether if
I can't rely on Tk to manage memory.
IMHO it's quite surprising if .destroy doesn't free all the resources
used by a widget!
Thanks
--
John
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