QSignalSpy stops debugger without any error message

[bodote]

Type: Bug

Behaviour

Debugging lines at and after QSignalSpy breaks the debugger, it quits without any error message.
signal_emitter = SignalEmitter() spy = QSignalSpy(signal_emitter.xPlaneAddrPortSignal)

Steps to reproduce:

import sys
from PySide6.QtWidgets import QApplication, QWidget
from PySide6.QtCore import QObject, Signal, SignalInstance
from PySide6.QtNetwork import QHostAddress
from PySide6.QtTest import QSignalSpy

class SignalEmitter(QObject):
    xPlaneAddrPortSignal = Signal(QHostAddress, int)

class CustomWidget(QWidget):
    def __init__(self):
        super().__init__()
        # Initialize your custom widget here

def main():
    # app = QApplication(sys.argv)
    app = QApplication(sys.argv)
    app.processEvents()
    widget = CustomWidget()
    widget.show() 
    signal_emitter = SignalEmitter()
    spy = QSignalSpy(signal_emitter.xPlaneAddrPortSignal)

    def signal_handler(host: QHostAddress, port: int):
        print(f"Signal emitted: Host - {host.toString()}, Port - {port}")

    signal_emitter.xPlaneAddrPortSignal.connect(signal_handler)    
    # To emit the signal (for testing purposes):
    signal_emitter.xPlaneAddrPortSignal.emit(QHostAddress("127.0.0.1"), 8080)
   
    if spy.count() >= 1:
        print("spy.count() >=1")
    print("the end")
    sys.exit(app.exec())
   

if __name__ == "__main__":
    main()

start debugger in VSCode 1.93.0 with Python Debugger v2024.10.0
set breakpoint at spy = QSignalSpy(signal_emitter.xPlaneAddrPortSignal) , then press "next" in debugger controls
set breakpoint at print("the end") and press "continue"

the debugger quits without any message before it reaches print("the end") . but when running the program without the debugger, it works just fine.

Diagnostic data

```` 2024-09-10 08:44:32.248 [info] DAP Server launched with command: /Users/bodo.teichmann/dev/flightsim_raspi/pyG5/.venv/bin/python /Users/bodo.teichmann/.vscode/extensions/ms-python.debugpy-2024.10.0-darwin-arm64/bundled/libs/debugpy/adapter 2024-09-10 08:44:32.392 [info] Received 'debugpySockets' event from debugpy. 2024-09-10 08:44:32.393 [info] Received 'debugpySockets' event from debugpy. 2024-09-10 08:44:32.395 [info] Received 'debugpySockets' event from debugpy. 2024-09-10 08:44:32.942 [info] Received 'debugpySockets' event from debugpy. 2024-09-10 08:44:38.921 [info] Received 'debugpySockets' event from debugpy. 2024-09-10 08:44:38.922 [info] Received 'debugpySockets' event from debugpy. ```

launch.json configuration

not used `launch.json`, just used "Python Debugger: Python File"

XXX

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

XXX

Output for Python Debugger in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python Debugger)

XXX

Extension version: 2024.10.0
VS Code version: Code 1.93.0 (Universal) (4849ca9bdf9666755eb463db297b69e5385090e3, 2024-09-04T13:02:38.431Z)
OS version: Darwin arm64 23.6.0
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.12.3
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): VirtualEnvironment

System Info

Item	Value
CPUs	Apple M1 (8 x 2400)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	1, 4, 4
Memory (System)	16.00GB (0.05GB free)
Process Argv	--crash-reporter-id 41815999-c6d4-4cd1-a9ae-96ab587a20ec
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
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binariesv615:30325510
vsaa593cf:30376535
py29gd2263:31024239
c4g48928:30535728
azure-dev_surveyone:30548225
2i9eh265:30646982
962ge761:30959799
pythongtdpath:30769146
welcomedialog:30910333
pythonnoceb:30805159
asynctok:30898717
pythonmypyd1:30879173
2e7ec940:31000449
pythontbext0:30879054
accentitlementst:30995554
dsvsc016:30899300
dsvsc017:30899301
dsvsc018:30899302
cppperfnew:31000557
dsvsc020:30976470
pythonait:31006305
dsvsc021:30996838
jg8ic977:31013176
a69g1124:31058053
dvdeprecation:31068756
dwnewjupyter:31046869
impr_priority:31102340
nativerepl1:31104043
refactort:31108082
pythonrstrctxt:31112756
flighttreat:31119336
wkspc-onlycs-t:31132770
wkspc-ranged-t:31125599
fje88620:31121564

[bodote]

found a not pleasant work around:
instead of using spy = QSignalSpy(signal_emitter.xPlaneAddrPortSignal) and spy.wait(), I used
loop = QEventLoop() and loop.exec() , that also works with the debugpy, although this solution is more cumbersome.

[judej]

@bodote, this is likely due to way QSignalSpy pauses execution when you call spy.wiat() while it waits for the signal to be emitted. Debugpy likely does not deal with the blocking wait correctly and exits prematurely.

Since you've found that replacing QSignalSpy with QEventLoop fixes the debugger quitting issue, it suggests that QSignalSpy’s internal handling of signal emissions (even without explicitly using wait()) may interfere with the debugger's ability to manage the Qt event loop correctly.

Hope this helps, alas there isn't a less cumbersome workaround.

thanks