GUI widgets are not garbadge collected

[eruvanos]

UIWidgets bind own methods to themselves,
which creates a strong reference, which prevents garbadge collection.

Code to reproduce

import gc
from arcade.gui import UIWidget

widget = UIWidget()
widget.add(UIWidget())

del widget
gc.collect()

amount_of_widgets = len([obj for obj in gc.get_objects() if isinstance(obj, obj_type)])
assert amount_of_widgets == 0

[eruvanos]

Options to fix this:

A) always weak
bind could always use weak reference, which would work for callbacks which are still referenced, but in case somebody uses an anonoumous function, that would just vanish. To reduce the risk, bind() could have a parameter weak, which could be false

This is what kivy does, beside the weak param

B) always strong
bind could always use strong reference, like today. To fix the current situation, bind() could have a parameter weak, which could be False by default

C) "mixed" behaviour
bind could check if the callback is a function (not bound to an object) or a method (bound to a class). And reference functions strong and methods weak.
For special cases we could still provide the weak parameter.

D) "smart" behaviour
bind might be able to check, that a method is bound to itself and use weak references in that case.

Further thoughts:
I personally prefer (B) which is backwards compatible and is more explicit. It could still lead to memory leaks, but would prevent listeners just vanishing.

[eruvanos]

Introducing weak references seems to cause performance issues, raising the execution time from 0.3 sec to 0.7 sec:

from time import perf_counter

from arcade import LRBT
from arcade.gui import bind, UIWidget

for j in range(10):
    # This is just to ensure that the module is loaded and the UIWidget class is defined.
    start = perf_counter()
    widget = UIWidget()

    counter = 0

    def act():
        global counter
        counter += 1

    bind(widget, "rect", act)

    for i in range(100000):
        widget.rect = LRBT(0, 0, 100, i)

    end = perf_counter()
    print(f"Time taken for 100000 updates: {end - start:.4f} seconds")


# development: Time taken for 100000 updates: 0.1780 seconds
# gui/fix-memory-leak:      Time taken for 100000 updates: 0.3511 seconds

[eruvanos]

Next idea:

storing listeners on the object, so, they would get garbage collected.

Instead of binding widget.method we can bind UIWidget.method.
Due to the new supported call arguments such methods would be called with the instance first, which would bind to the self parameter

[eruvanos]

Better performance:

# gui/fix-memory-leak: Time taken for 100000 updates: 0.1821 seconds