What part of asyncio is concurrent? Would like implementation details

Question

The description of the asyncio module is:

This module provides infrastructure for writing single-threaded concurrent code using coroutines, multiplexing I/O access over sockets and other resources, running network clients and servers, and other related primitives.

I have been reading about the new and extraordinary asyncio python module/package/whatever. I understand there is the python GIL and so the asyncio properly fits well with the GIL since (the intention is) you manage things with an event loop on a single thread. So what is concurrent? Well it seems that the I/O seems to be concurrent. I believe I/O operations are handled by the operating system. So in the internals of asyncio, does it write a concurrent C-extension that utilizes functions given by the operating system?

Answer 1

In asyncio, single-threaded IO concurrency is achieved by combining many concepts:

future -------------------+---------+
                          |         |
generator ---> coroutine -+-> task -+-> base event loop -+-> selector event loop
                                                         |
select ---> selector ------------------------------------+

However, it is possible to achieve the same purpose without futures, as proven by curio:

generator ---> coroutine -+-> task -+-> kernel
                                    |
select ---> selector ---------------+

---

Links

Standard library:

• generator
• select
• selector
• native coroutine

Asyncio:

• asyncio coroutine
• asyncio future
• asyncio task
• base event loop
• selector event loop

Curio:

• curio coroutine
• curio task
• curio kernel