Tkinter long-running window freezes

[John O'Hagan]

On Sat, 27 Feb 2021 01:06:06 +0000
MRAB <python at mrabarnett.plus.com> wrote:

> On 2021-02-26 23:59, John O'Hagan wrote:
> > 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!
> >   
> I've look in Lib\tkinter\__init__.py and it appears that you can give
> it a name, so:
> 
> from tkinter import *
> from random import randint
> 
> root = Tk()
> 
> def display(label):
>       label.destroy()
>       label = Label(name='my_label', text=randint(0, 9))
>       label.pack()
>       root.after(1, display, label)
> 
> display(Label(name='my_label'))
> mainloop()
> 
> When I do that I'm not seeing a memory rise.

I just did the exact same thing, also saw no memory rise, but the
window still froze after a couple of hours. Did your window freeze?
Maybe the memory rise and the freeze are unrelated after all.

Also, I was mistaken about Christian's second version of the Tcl code
above - there is no memory rise but the window also freezes after a
while. Suggests the problem is in Tcl/Tk.

Thanks

--

John