PlotItem leak since PySide6 6.5.0

[pijyoi]

Short description

Since PySide6 6.5.0, some objects within PlotItem will be leaked when PlotItem is destroyed.

This issue is a spinoff from #2665 as this issue is specific to PySide6 6.5.0.

Code to reproduce

Additional psutil library is used to show memory growth.

import pyqtgraph as pg
from pyqtgraph.Qt import QtCore
import psutil

app = pg.mkQApp()
timer = QtCore.QTimer()
proc = psutil.Process()

rss0 = proc.memory_info().rss

cnt = 0
def timer_cb():
    global cnt
    rss = proc.memory_info().rss
    print(f'{cnt}: {(rss - rss0)/1048576:.1f} MB')
    pg.PlotItem()
    cnt += 1
    if cnt > 100:
        timer.stop()
        app.exit()

timer.timeout.connect(timer_cb)
timer.start(0)
pg.exec()

Expected behavior

Memory usage should stabilize.

Real behavior

Memory usage continues to grow with each iteration.

Tested environment(s)

• PyQtGraph version: master
• Qt Python binding: PySide6 6.5.0
• Python version: Python 3.10.10
• NumPy version: 1.24.2
• Operating system: Windows 11
• Installation method: pip

Additional context

Doesn't occur for PySide2 5.12.2, PyQt5 5.15.9, PySide6 6.4.3, PyQt6 6.4.2

[pijyoi]

No leak for PyQt6 6.5.0 either.

[pijyoi]

Minimal pyqtgraph-free script that leaks on PySide >= 6.5.0

from PySide6 import QtCore, QtWidgets
import psutil

class Leaker:
    def __init__(self):
        parent = None
        parent = QtWidgets.QWidget()    # this line seemingly makes PySide < 6.5.0 not leak
        wgt= QtWidgets.QSpinBox(parent)
        wgt.valueChanged.connect(self.mkChangeCallback(wgt))

    def mkChangeCallback(self, w):
        return lambda *args: self.widgetChanged(w, *args)
        
    def widgetChanged(self, w, *args):
        pass

app = QtWidgets.QApplication([])
timer = QtCore.QTimer()
proc = psutil.Process()

rss0 = proc.memory_info().rss

cnt = 0
def timer_cb():
    global cnt
    rss = proc.memory_info().rss
    print(f'{cnt}: {(rss - rss0)/1048576:.1f} MB')
    Leaker()
    cnt += 1
    if cnt > 500:
        timer.stop()
        app.exit()

timer.timeout.connect(timer_cb)
timer.start(0)
app.exec() if hasattr(app, 'exec') else app.exec_()

[adrianghc]

Hi, I'm one of the maintainers of Qt for Python. I'm currently investigating the leak and have reduced your script even further. The following code leaks on PySide >= 6.5.0, but not below:

from PySide6 import QtCore, QtWidgets


class Leaker:
    def __init__(self):
        widget = QtWidgets.QWidget()
        widget.windowIconChanged.connect(lambda *args: None)


app = QtWidgets.QApplication()
timer = QtCore.QTimer()
timer.timeout.connect(Leaker)
timer.start()
app.exec()

I'd like to encourage you to create a bug report in our JIRA detailing your findings. Feel free to assign it to me. Thank you very much for discovering this leak. 😊

[j9ac9k]

Hi @adrianghc

The difference is the reference to self. We ran into this problem in another part of the library some eons ago and decided to just work around it at the time. We should have reported upsteam them, sorry!

[adrianghc]

We believe we have now fixed this bug: https://bugreports.qt.io/browse/PYSIDE-2299 It will be part of the PySide 6.5.1 release. Thank you for your patience, and let us know if you continue to have problems.

[pijyoi]

fixed in PySide 6.5.1 but also worked around in #2694