asyncio: What is the difference between tasks, futures, and coroutines?

[Marko Rauhamaa]

Paul  Moore <p.f.moore at gmail.com>:

> But I don't understand what a Future is.

A future stands for a function that is scheduled to execute in the
background.

Personally, I have never found futures a very useful idiom in any
language (Scheme, Java, Python). Or more to the point, concurrency and
the notion of a function don't gel well in my mind.

See also: <URL: http://en.wikipedia.org/wiki/Futures_and_promises>

> A Task is a subclass of Future, but the documentation doesn't say what
> it *is*,

A task is almost synonymous with a future. It's something that needs to
get done.

--

I think asyncio is a worthwhile step up from the old asyncore module.
Its main advantage is portability between operating systems. Also, it
has one big advantage over threads: events can be multiplexed using
asyncio.wait(return_when=FIRST_COMPLETED).

However, I happen to have the privilege of working with linux so
select.epoll() gives me all the power I need to deal with asynchrony.
The asyncio model has the same basic flaw as threads: it makes the
developer think of concurrency in terms of a bunch of linear streaks of
execution. I much prefer to look at concurrency through states and
events (what happened? what next?).

My preferred model is known as "Callback Hell" (qv.). Asyncio seeks to
offer a salvation from it. However, I am at home in the Callback Hell;
equipped with Finite State Machines, the inherent complexities of the
Reality are managed in the most natural, flexible manner.


Marko