python -m asyncio fails

[rogerbinns]

Run python -m asyncio

There will be an exception based on calling termios.tcgetattr

[holzschu]

Hi,
I've had a look, and I don't think I'll be able to fix that one: it's related to the fact that asyncio uses threads for parallel entry, and I'm already using threads as a replacement for forks.

"python" (alone) works, and has a REPL console, but a-Shell is not made for asynchronous things.

[rogerbinns]

Thanks for looking into this. Regular Python threading does work. And async by itself also works:

async def foo(x,y):
    return x+y

import asyncio
print(asyncio.run(foo(1,2))

I figured the underlying issue is termios.tcgetattr as I've seen mentioned in other issues.

You can also get a similar tcgetattr traceback with regular python:

>>> import threading
>>> threading.Thread(target=input, args=("prompt ",)).start()

On desktop interactive Python that will also exception, but because it doesn't like concurrent poll and signal operations not on the main thread.

ie it looks like python -m asyncio should work providing tcgetattr doesn't error.

[holzschu]

Yes, threading works (mostly...) but specifically asynchronous input/output does not work: stdin/stdout have been redefined as thread-local variables, which allows us to emulate multi-processing using threads, but the flipside is that when Python starts a new thread, then stdin/stdout are not defined. That's (as far as I can tell) the issue with the tcgetattr in asyncio: it's trying to access a stream that is not opened.

[rogerbinns]

Ok, that makes sense. The asyncio event loop is being run in the main thread and the REPL in a secondary thread then. I'm perfectly happy for you to close this as not practical.

One question though is if when a thread is created, can you copy over the stdio handles into the new thread during the thread creation process?