Kvaser Shutdown Error With Multiple Tasks

[johanbrus]

I observed (on python-can 3.3.3 / Python 3.7.0) that with multiple periodic tasks, when calling the shutdown() function for a kvaser interface, the following error message is shown, maybe :

RESTART: testfile.py 
Message sent on Kvaser Memorator, S/N XXXX (#1)
>>> Function canWrite failed - Handle is invalid
Traceback (most recent call last):
  File "C:\Program Files\Python37\lib\site-packages\can\broadcastmanager.py", line 136, in _run
    self.bus.send(self.message)
  File "C:\Program Files\Python37\lib\site-packages\can\interfaces\kvaser\canlib.py", line 555, in send
    flags)
  File "C:\Program Files\Python37\lib\site-packages\can\interfaces\kvaser\canlib.py", line 99, in __check_status
    raise CANLIBError(function, result, arguments)
can.interfaces.kvaser.canlib.CANLIBError: Function canWrite failed - Handle is invalid

Does anyone have any idea?

Code for issue reproduction:
(with only one task, there is no error message)

import can
import time

from can.bus import BusABC

def send_periodic(bus_a):
    
    msg1 = can.Message(arbitration_id=0x444,
                      data=[0, 25, 0, 1, 3, 1, 4, 1],
                      is_extended_id=False)

    msg2 = can.Message(arbitration_id=0x454,
                      data=[1, 26, 1, 2, 4, 2, 5, 2],
                      is_extended_id=False)

    msg3 = can.Message(arbitration_id=0x464,
                      data=[2, 27, 2, 3, 5, 3, 6, 3],
                      is_extended_id=False)    

    try:
        #task1 = bus_a.send_periodic(msg1, 0.3)
        task2 = bus_a.send_periodic(msg2, 0.5)
        task3 = bus_a.send_periodic(msg3, 1.0)
        if not isinstance(task1, can.ModifiableCyclicTaskABC):
            print("This interface doesn't seem to support modification")
            task1.stop()
            return
        counter=0
        while counter<10:
            msg2.data[0] = msg2.data[0] + 1
            task2.modify_data(msg2)
            time.sleep(1)
            counter+=1    
        print("Message sent on {}".format(bus.channel_info))
    except can.CanError:
        print("Message NOT sent")

if __name__ == '__main__':
    counter=0
    bus = can.interface.Bus(bustype='kvaser', channel=0, bitrate=250000)
    send_periodic(bus)
    time.sleep(10)
    bus.stop_all_periodic_tasks()
    bus.shutdown()

[karlding]

I don't have a Kvaser interface, but I suspect there is a race in your code between when stop_all_periodic_tasks is called and when you call shutdown. Skimming through the code for the Kvaser interface, it looks like stop_all_periodic_tasks currently is non-blocking, so it's possible that shutdown is called while a send is still pending.

Just to confirm that this isn't what's causing the issue and collect some more data, can you verify that this still reproduces if you add a barrier between stop_all_periodic_tasks and the shutdown (or a time.sleep)?