Bug/Improvement: Correct handling of message sending

[martenrichter]

Recently a lot of bug reports regarding jupyter lite widget interactivity being broken:
#133
jupyterlite/jupyterlite#1465
jupyter-book/thebe#771
jupyter/try-jupyter#54

I have ran jupyter lite for two days in the debugger (see here my post about it here:
#133
).

And I am now relatively confident that the incomplete implementation of ``get_parentinkernel.py` and the js side:

pyodide-kernel/packages/pyodide-kernel/py/pyodide-kernel/pyodide_kernel/kernel.py

Line 29 in b70f099

def get_parent(self):

is causing the trouble. As the control and shell channel parent is mixing through this simplification.
In contrast to:
https://github.com/ipython/ipykernel/blob/188f39c509f1056c3784aad6954498f31de955a3/ipykernel/kernelbase.py#L622

So I think that a patch for this behavior is required. And this may fix the issues. Do you agree?

Are you open for PR? (But I must say, I am very experienced in C++ and js (and a bit in ts), but not in python, but I think the changes do not require much understanding of the language details, so it is possible that I will give up, if I fail). Also I am not so sure how I can test the changes on pyodide-kernel alone. So input is appreciated.

P.S: I hope it is ok to open a separate issue, I thought in this way it is a bit more organized.

[martenrichter]

Ok, I tried to implement it. But it was not the cause. Anyway, the wrong ordering of message with their kernel header is the cause. I also tried to reuse the parent headers from the initial execution attempt, but this did not work either (xeus has always the same parent msg_id, so I gave it a try). I will continue....

[martenrichter]

Sorry for the erratic diagnosis posts. It has to something to do with the message sending order.
I have identified the problematic commit:
42e18ca

I would assume that replacing the post message changes the order or timing. I am sorry that I can not provide the exact cause. But for now, reverting the commit makes interactive widgets functional again.
So I recommend reverting it, and then merging a fixed change later.

[martenrichter]

[Delete was just the browser cache...]

[martenrichter]

Additional things:
1.) Use test code:

%pip install -q ipywidgets
from ipywidgets import interact

# Function to handle text input
def display_text(value=''):
    return f"Updated value: {value}"

# Create an interactive Text widget
interact(display_text, value='Type something...');

Hit two keys on the keyboard simultaneously (I used for example g and h next to each other on my German keyboard), I can provoke the problem with 90% chance.
2.) I am not sure, if the message sending is really atomic in worker.ts. So are all transactions hidden in setup immediately or is there a message sending beneath it, when passing the parent header to python? THis may be the cause beneath the problem.

[martenrichter]

Fixed by #148