AsyncIO Code works in Python code but not in MicroPython

[neliel123]

I have just started exploring MicroPython specifically AsyncIO concepts.

I have written this code and tried running it in both CPython and MicroPython environments using the latest firmware but I don't know why the output is different.

import asyncio

sample_global = 0

async_event = asyncio.Event()

async def update_globals():
    global sample_global
    print('Function Started...')

    await async_event.wait()
    print('Sleep...Before Updating...')

    await asyncio.sleep(1)
    print('Updating...')

    sample_global += 1
    print('Done Updating...')

async def main():

    tasks = [update_globals() for _ in range(5)]

    asyncio.gather(*tasks)

    await asyncio.sleep(2)  # Simulating some time before allowing updates
    async_event.set()

    await asyncio.sleep(2)
    print(f"Final value of sample_global: {sample_global}")

if __name__ == "__main__":
    asyncio.run(main())

The output in CPython is Final value of sample_global: 5
But in MicroPython it is Final value of sample_global: 0

Any hints?

[peterhinch]

gather is a coroutine. The following works under CPython and MP:

import asyncio

sample_global = 0

async_event = asyncio.Event()

async def update_globals():
    global sample_global
    print('Function Started...')

    await async_event.wait()
    print('Sleep...Before Updating...')

    await asyncio.sleep(1)
    print('Updating...')

    sample_global += 1
    print('Done Updating...')

async def foo(tasks):
    await asyncio.gather(*tasks)

async def main():

    tasks = [update_globals() for _ in range(5)]
    asyncio.create_task(foo(tasks))

    await asyncio.sleep(2)  # Simulating some time before allowing updates
    async_event.set()

    await asyncio.sleep(2)
    print(f"Final value of sample_global: {sample_global}")

if __name__ == "__main__":
    asyncio.run(main())

[neliel123]

gather is a coroutine.

Hi Peter,
Maybe I don't get it that much. Many of the tutorials I am following are in CPython format as there are more tutorials about AsyncIO in there.

Is this a MicroPython quirk so it does not work as per the CPython tutorials that I have been following on the net? This is so that I could take note of this.
Thanks for replying

[peterhinch]

See CPython docs where gather is defined as an awaitable. The original code has a bug where gather is called as if it were a function. With this bug fixed, MP and CPython behave identically. At the moment I can't see a quirk.

For a MicroPython asyncio tutorial see this doc.

[neliel123]

Hey,
So if gather is an awaitable then I could await on it?

async def main():

    tasks = [update_globals() for _ in range(5)]

    await asyncio.gather(*tasks)

    await asyncio.sleep(2)  # Simulating some time before allowing updates
    async_event.set()

    await asyncio.sleep(2)
    print(f"Final value of sample_global: {sample_global}")

Tried this, and I am seeing a different output.

Function Started...
Function Started...
Function Started...
Function Started...
Function Started...

It did not print the final value.

[peterhinch]

The tasks have started but are waiting on the Event. The gather only terminates when all the tasks have terminated, so the Event never gets triggered. The code therefore waits forever. That's why I delegated await gather(...) to a concurrent task (foo()).