Segfault with Python/Linux

[dsandber]

I'm getting a SEGFAULT:

Code: Select all

#0  0x000000003b9acc04 in ?? ()
#1  0x0000000000494468 in _PyObject_MakeTpCall ()
#2  0x0000007fab656910 in ?? () from /usr/lib/python3.11/lib-dynload/_ctypes.cpython-311-aarch64-linux-gnu.so
#3  0x0000007fab616190 in ?? () from /lib/aarch64-linux-gnu/libffi.so.8
#4  0x0000007fab616574 in ?? () from /lib/aarch64-linux-gnu/libffi.so.8
#5  0x0000007f883ff238 in ?? () from /lib/aarch64-linux-gnu/libphidget22.so.0
#6  0x0000007f884ad9e4 in ?? () from /lib/aarch64-linux-gnu/libphidget22.so.0
#7  0x0000007f8846afcc in ?? () from /lib/aarch64-linux-gnu/libphidget22.so.0
#8  0x0000007fac2cee30 in start_thread (arg=0x7f127ce417) at ./nptl/pthread_create.c:442
#9  0x0000007fac337adc in thread_start () at ../sysdeps/unix/sysv/linux/aarch64/clone.S:79

On Linux:

6.6.31-rt31-v8+ #5 SMP PREEMPT_RT Wed Jul 31 20:16:24 CEST 2024 aarch64 GNU/Linux

Using the newest? library version:

> dpkg -l | grep phid
ii libphidget22:arm64 99:1.22.20250106-1+deb12 arm64 Phidgets runtime library

Any idea what might cause this? How to fix it?

[Patrick]

Hi,

What Phidgets are you using? Can you share a code sample that causes the crash?

-Patrick

[dsandber]

I'll post more information once I have it, probably on Wednesday.

No Python stack-trace was provided presumably because I didn't have "faulthandler" enabled and the segfault happened in a non-main thread.

Thanks for the help!

[dsandber]

Code: Select all

distance_sensor.setOnDistanceChangeHandler(None)
distance_sensor.setOnDistanceChangeHandler(BlahSensor.on_distance_change)

Seems like the code's author (not me) is setting the OnDistanceChangeHandler to None and then to a certain method repeatedly in the code. This seems fishy to me, and I'll change it, but it still shouldn't cause a segfault either.

So presumably there's a race condition where there's a tiny bit of time where the change handler is set to None and that causes a segfault. Which it shouldn't. Be also it's stupid to be setting it to None...

[dsandber]

Confirmed. Was able to get a segfault on a mac with this code:

Code: Select all

import time
from Phidget22.Phidget import *
from Phidget22.Devices.DistanceSensor import *


# Event handler for when the sensor has a new distance value
def onDistanceChange(distanceSensor, userData):
    print(f"Distance: {distanceSensor.getDistance()} cm")


def main():
    try:
        # Create a distance sensor object
        distanceSensor = DistanceSensor()

        # Set up event handler for distance change
        distanceSensor.setOnDistanceChangeHandler(onDistanceChange)

        # Open the sensor for device communication
        distanceSensor.openWaitForAttachment(5000)
        distanceSensor.setDataInterval(100)

        # Wait for 10 seconds to collect distance data
        print("Collecting distance data... Press Ctrl+C to exit.")
        while True:
            time.sleep(0.001)
            distanceSensor.setOnDistanceChangeHandler(None)
            time.sleep(0.001)
            distanceSensor.setOnDistanceChangeHandler(onDistanceChange)

    except PhidgetException as e:
        print(f"Phidget Exception: {e}")

    finally:
        # Close the sensor
        distanceSensor.close()


if __name__ == "__main__":
    main()

[Patrick]

Thanks for reporting, this is fixed for the next release.

-Patrick