Tkinter wait_visibility hanging when used in thread

[spcmicro]

BPO	42491
Nosy	@terryjreedy, @serhiy-storchaka, @E-Paine, @spcmicro
Files	threadTest.zip: Contains source files and screen captures

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-11-28.10:27:46.332>
labels = ['3.8', 'type-bug', 'expert-tkinter', '3.9', '3.10']
title = 'Tkinter wait_visibility hanging when used in thread'
updated_at = <Date 2021-08-19.12:59:09.651>
user = 'https://github.com/spcmicro'

bugs.python.org fields:

activity = <Date 2021-08-19.12:59:09.651>
actor = 'spcmicro2'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tkinter']
creation = <Date 2020-11-28.10:27:46.332>
creator = 'spcmicro'
dependencies = []
files = ['49631']
hgrepos = []
issue_num = 42491
keywords = []
message_count = 6.0
messages = ['381990', '382001', '382006', '382011', '399873', '399914']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'serhiy.storchaka', 'epaine', 'spcmicro', 'spcmicro2']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42491'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

Linked PRs

• gh-86657: Add a timeout parameter to tkinter wait_visibility() #152621

[spcmicro]

I'm having a problem with an application that uses threads and TKinter. Sometimes everything works fine but there are 2 errors that I can't seem to figure out why they are happening. The first error is the GUI completely locking up with no text cursor in the textbox. The second problem is a crash after the input has been entered.
I have created a bare minimum test application that demonstrates the problem. The problems are easily reproducible.
I've attached a simpleteTKinter test application that I created using Page. I've also attached 3 screen captures.

1. threadTest-OK.jpg is proper behavior
2. threadTest-Hung.jpg shows the unresponsive application
3. threadTest-Exception.jpg shows the exception thrown when input window is closed
   It looks like a race condition to me. I've tried putting in delays and using after but I can't seem to work around it.
   Am I doing something wrong here?

[E-Paine]

I agree this is a race condition, and have narrowed the issue down to wait_visibility with the following also hanging indefinitely (tested against the master branch):

import threading
import tkinter as tk
def create_tp():
    t = tk.Toplevel()
    t.wait_visibility()
root = tk.Tk()
tk.Button(root, text="Create", command=lambda:
          threading.Thread(target=create_tp).start()).pack()
root.mainloop()

I agree this is a race condition (presumably between wait_visibility and window render) and am pretty sure there is nothing either us or the Tk team can do (IMO, this issue should be closed - though thank you for reporting it).
Similar behaviour to issue-42142, though I don't believe threading is used there.

Am I doing something wrong here?
Using threads?! tkinter is known to not like threads and there are several bugs which can cause the Python interpreter to crash.