No need to use tp_alloc and tp_free, because these types are not valid base types. Just make them immutable.

Doesn't it mean I would leave the possibility of introducing a cycle in bug fix versions and simply make them all immutable in main? unlike the select.[e]poll and _random.Random, the trace function can have a reference to the current app.

Now, you added tk.settrace as an experimental feature so it's internal only, but I believe that making it non-experimental would still require tp_clear/tp_traverse (and thus tp_alloc/tp_free as recommended by the docs; otherwise I would need GC_New/GC_Del + track).

Ok, now I'm utterly confused because I don't understand why I get a segfault. The segfault happens in PyObject_GC_UnTrack

Well.. that's what I wanted to do but now the docs say to do things differently and considering people take inspiration for their extension modules with CPython code it'd be better to match our recommendations. Personally, I would prefer using the exact functions instead of tp_free/tp_alloc.

Please create a DPO post to gauge feedback on whether to use tp_alloc/tp_free vs manual allocation functions.

Well, if you want to use tp_alloc/tp_free, can you just use them, without adding unnecessary lines?

Oh you mean, removing the asserts. Well, I can do it though tracking segfaults would be a bit more annoying (at least with asserts, we don't have this issue). I'll just shorten the diff then and let it segfault normally.

Debuggers are typically pretty good at catching null pointer dereferences anyway.

(I merged main because of conflicts; for the backports, I will need to do them manually as those types are not immutable on 3.13 and 3.14).

Mmh, something is actually wrong now. Previously, those leaked:

import tkinter
w = tkinter.Tk()
trace = lambda *_, **__: None
trace.evil = type(w.tk)
w.tk.settrace(trace)
w.mainloop()

For the timer, it's also possible to make something bad as follows:

import tkinter
w = tkinter.Tk()
func = lambda *_, **__: None
func.evil = type(w.tk.createtimerhandler(1234567, print))
w.tk.createtimerhandler(1234567, func)
w.mainloop()

But now I have the following crash for the timer reproducer:

python: ./Modules/_tkinter.c:2784: int Tktt_Traverse(PyObject *, visitproc, void *): Assertion `TkttObject_Check(op)' failed.

The first reproducer is fixed however. I think it's because of the extra reference created by the timer handler that is not properly visited or decrefed. I'll first patch this crash and move to backports afterwards.

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 CentOS9 NoGIL Refleaks 3.x (tier-1) has failed when building commit f96f7c9.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1610/builds/2057) and take a look at the build logs.
4. Check if the failure is related to this commit (f96f7c9) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1610/builds/2057

Failed tests:

• test_free_threading

Test leaking resources:

• test_free_threading: file descriptors

Summary of the results of the build (if available):

==

remote: Enumerating objects: 3, done.        
remote: Counting objects:  50% (1/2)        
remote: Counting objects: 100% (2/2)        
remote: Counting objects: 100% (2/2), done.        
remote: Total 3 (delta 1), reused 1 (delta 1), pack-reused 1 (from 1)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to 'f96f7c9f5b5db35e8a22f29b4e20f386cdde64f5'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at f96f7c9f5b5 Revert "gh-116946: fully implement GC protocol for `_tkinter.Tk{app,tt}Object` (#138331)" (#138807)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdec found; falling back to pure-Python version for the decimal module

make: *** [Makefile:2486: buildbottest] Error 2