Python-object is not garbage collected when used with EventListener #693
Description
Hi!
I have a special case here regarding garbage collection in combination with JavaScript's addEventListener and removeEventListener functions.
- Creating an instance of a class, associating it with a DOM element and removing it again works - the object is entirely freed.
- Creating an instance of a class, associating it with a DOM element, attaching an event to it and detaching it immediately after still holds a reference to it the object, even if it is explicitly removed with
del
I guess, that the problem here is in JavaScript, which still holds a reference and this is normal with JavaScript. But I'm quite unsure, and would like to ask for further investigation, eventually its really a bug.
Test case is this Python script. Attached is bug.txt
to be renamed bug.html, which can be copied into the build/ folder and directly be executed.
from js import document
import weakref, gc
print("start")
class TestWrapper:
def __init__(self):
super().__init__()
self.div = document.createElement("div")
def testCallback(self, event):
print("Got Event")
def attach(self):
print("attach")
self.div.addEventListener("click", self.testCallback)
def detach(self):
print("detach")
self.div.removeEventListener("click", self.testCallback)
def __del__(self):
print("I am removed")
print("---111---")
div = TestWrapper()
rw = weakref.ref(div)
gc.collect()
print("1 Weakref resolves to: %s" % rw())
del div
gc.collect()
print("1 Weakref after dropped reference resolves to: %s" % rw()) # << this is None, as expected!
print("---222---")
div = TestWrapper()
rw = weakref.ref(div)
div.attach()
del div
gc.collect()
print("2 Weakref to Wrapper-Class with active event listener: %s" % rw())
rw().detach()
gc.collect()
print("2 Weakref to Wrapper-Class with removed event listener: %s" % rw()) # << At least this should be NoneThe logging output in the JavaScript console is this:
Python initialization complete
start
---111---
1 Weakref resolves to: <TestWrapper object at 0x9a8a60>
I am removed
1 Weakref after dropped reference resolves to: None
---222---
attach
2 Weakref to Wrapper-Class with active event listener: <TestWrapper object at 0x9a8a60>
detach
2 Weakref to Wrapper-Class with removed event listener: <TestWrapper object at 0x9a8a60>
It can be reproduced both in Firefox 77.0.1 and Chromium Version 83.0.4103.97