Getting started on asyncio
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Descrizione
I've been trying to understand how this project works, and also how we can support newer language versions. I've done some reading into how asyncio works, and I thought I would share that here. Sorry if this is not news to anybody, I'm not much of a python developer.
The co-routine introduced in python3.5 seem to be the biggest language feature we need to support to become current. The op codes can be found here: https://docs.python.org/3/library/dis.html#opcode-GET_AWAITABLE
A basic example program looks like:
```
import asyncio
async def foo():
return "test"
async def bar():
return await foo()
print(asyncio.run(bar()))
```
And produces the following bytecode:
```
1 0 LOAD_CONST 0 (0)
2 LOAD_CONST 1 (None)
4 IMPORT_NAME 0 (asyncio)
6 STORE_NAME 0 (asyncio)
3 8 LOAD_CONST 2 ()
10 LOAD_CONST 3 ('foo')
12 MAKE_FUNCTION 0
14 STORE_NAME 1 (foo)
6 16 LOAD_CONST 4 ()
18 LOAD_CONST 5 ('bar')
20 MAKE_FUNCTION 0
22 STORE_NAME 2 (bar)
10 24 LOAD_NAME 3 (print)
26 LOAD_NAME 0 (asyncio)
28 LOAD_METHOD 4 (run)
30 LOAD_NAME 2 (bar)
32 CALL_FUNCTION 0
34 CALL_METHOD 1
36 CALL_FUNCTION 1
38 POP_TOP
40 LOAD_CONST 1 (None)
42 RETURN_VALUE
Disassembly of :
0 GEN_START 1
4 2 LOAD_CONST 1 ('test')
4 RETURN_VALUE
Disassembly of :
0 GEN_START 1
7 2 LOAD_GLOBAL 0 (foo)
4 CALL_FUNCTION 0
6 GET_AWAITABLE
8 LOAD_CONST 0 (None)
10 YIELD_FROM
12 RETURN_VALUE
```
The byte code of calling the functions is actually unchanged. The functions marked with `async` just have to return a co-routine object. The `GET_AWAITABLE` opcode seems to cast the other await-able types e.g. generators or classes that implement `self.__await__`.
We _might_ be able to implement this fairly easily by just wrapping the `Function` type in a `co-routine` type. To get any actual concurrency out of this implementation though, we need to implement the event loop API.
https://docs.python.org/3/library/asyncio-eventloop.html#:~:text=The%20event%20loop%20is%20the,asyncio%20functions%2C%20such%20as%20asyncio.
This is the hard part which actually allows creation of futures and tasks. I'm not sure if the `await for` byte code that was already implemented in 3.4 has all the features we need, but it looks like we can get pretty far with the byte code we have already.
The last piece of the puzzle is `select()` which allows us to wait on a socket while executing another co-routine.
There's a good write-up here:
https://stackoverflow.com/questions/49005651/how-does-asyncio-actually-work
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