Consider removing the thread and future handling in asyncio REPL

[frostming]

Bug report

Bug description:

In the current asyncio REPL, the event loop runs in the main thread, while the interactive console operates in a separate thread as both are running blocking loops. This leads to issues with console input handling, as noted in issue gh-140163 and gh-138827.

cpython/Lib/asyncio/__main__.py

Lines 226 to 240 in d86ad87

	repl_thread = REPLThread(name="Interactive thread")
	repl_thread.daemon = True
	repl_thread.start()
	while True:
	try:
	loop.run_forever()
	except KeyboardInterrupt:
	keyboard_interrupted = True
	if repl_future and not repl_future.done():
	repl_future.cancel()
	repl_thread.interrupt()
	continue
	else:
	break

While this is a MacOS-specific issue, it reveals a defect of the existing implementation. Specifically, the REPL can never receives Ctrl-C event and set the readline status properly, as it does normally. As the above code shows, the outer-most loop catches the KeyboardInterrupt and sets a flag, then tells the REPL to respond. However, the console loop never stops when this happens, because you can't actually interrupt input() from outside the thread, making it unable to respond to outer events.

So I rethink of the necessity of separate threads and also refer to the implementation of IPython. In a REPL, each cell is executed, and the result is awaited. There doesn't seem to be a need for a concurrent setup. A simple loop.run_until_complete() will do, as IPython does. At the same time, this can also greatly simplify the existing code.

However, I know I could be very wrong. So please correct me.

DPO link: https://discuss.python.org/t/consider-removing-the-thread-and-future-handling-in-asyncio-repl/104457

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-140355: Simplify asyncio REPL code by removing threading and future handling #140356

[sergey-miryanov]

I believe you have to discuss such changes on dpo (https://discuss.python.org/) first.
cc @kumaraditya303

[frostming]

@sergey-miryanov makes sense, I added the link in the content

[frostming]

It seems to be implemented this way from the very beginning, so maybe @1st1 can give some insights(I didn't find your handle on DPO)?

[kumaraditya303]

I am not very familiar with how the repl works so can't review this, perhaps @ambv or @pablogsal can review it

[pablogsal]

@ambv will take a look when he has some free cycles