QUERY · ISSUE

Unexpected asyncio code exec between exc in task and call of global asyncio crash handler

openby mirkoopened 2024-10-01updated 2024-10-01

bug

Port, board and/or hardware

unix and esp32

MicroPython version

MicroPython v1.23.0-preview.436.gc8021842c

Reproduction

import asyncio

class Loop():
    async def run(self):
        print("---", self.__class__.__name__, "---")

    async def run_forever(self):
        while True:
            try:
                await self.run()
                await asyncio.sleep(0.1)
            except Exception as exc:
                print("EEE", exc)
                raise

class Loop_1(Loop):
    pass

class Loop_2(Loop):
    async def run(self):
        await super().run()
        raise Exception("MOEP!")

class Loop_3(Loop):
    pass

def async_crash_hdlr(loop, ctx):
    # called when unhandled exceptions thrown in asyncio tasks.
    # this function is called from within a task running in the mainloop.
    print("Global asyncio exception handler called -> FREEZE")
    while True:
        pass

async def main():
    asyncio.get_event_loop().set_exception_handler(async_crash_hdlr)
    loop1 = Loop_1()
    loop2 = Loop_2()
    loop3 = Loop_3()
    print("Starting loop1")
    asyncio.create_task(loop1.run_forever())
    print("Starting loop2")
    asyncio.create_task(loop2.run_forever())
    print("Starting loop3")
    asyncio.create_task(loop3.run_forever())
    while True:
        print("--- MAINLOOP ---")
        await asyncio.sleep(1)

print("Entering main program")
asyncio.run(main())

Expected behaviour

Expected the defined global asyncio exception handler (async_crash_hdlr) being called immediately.

Expected output from above code (as per CPython3):

Entering main program
Starting loop1
Starting loop2
Starting loop3
--- MAINLOOP ---
--- Loop_1 ---
--- Loop_2 ---
EEE MOEP!
Global asyncio exception handler called -> FREEZE

Observed behaviour

Unexpected to me, between the exception being raised in Loop2 and async_crash_hdlr() being called, there is still asyncio code being executed, despite no fruther await or alike in between.
In this very case (code from) Loop3 is being run:

Entering main program
Starting loop1
Starting loop2
Starting loop3
--- MAINLOOP ---
--- Loop_1 ---
--- Loop_2 ---
EEE MOEP!
--- Loop_3 --- # <<<<<-------------------------
Global asyncio exception handler called -> FREEZE

Additional Information

No, I've provided everything above.

Code of Conduct

Yes, I agree

CANDIDATE · ISSUE

uasyncio gather() return_exceptions behaviour differs from CPython

closedby peterhinchopened 2021-09-16updated 2022-03-30

extmod

I think this is a regression. The following script produces an unexpected result in MicroPython:

try:
    import uasyncio as asyncio
except ImportError:
    import asyncio

async def will_stop(n):
    print('Runs to completion')
    for _ in range(6):
        await asyncio.sleep(1)
    return 2 * n

async def forever(n):
    print('forever() will be cancelled')
    while True:
        await asyncio.sleep(1)
        n += 1
    return n

async def do_cancel(task):
    await asyncio.sleep(3)
    print('About to cancel forever')
    task.cancel()

async def main():
    tasks = [asyncio.create_task(forever(70))]
    tasks.append(will_stop(21))
    asyncio.create_task(do_cancel(tasks[0]))
    res = None
    try:
        res = await asyncio.gather(*tasks, return_exceptions=True)
    except asyncio.CancelledError:
        print('Cancelled')
    print('Result: ', res)

asyncio.run(main())

CPython (expected behaviour):

adminpete@debian8:/mnt/qnap2/temp$ python3
Python 3.8.0 (default, Dec  6 2019, 16:20:13) 
[GCC 4.9.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import rats40
forever() will be cancelled
Runs to completion
About to cancel forever
Result:  [CancelledError(), 42]
>>>

MicroPython (behaves as if return_exceptions==False):

MicroPython v1.17 on 2021-09-02; linux version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> import rats40
forever() will be cancelled
Runs to completion
About to cancel forever
Cancelled
Result:  None
>>>