[Async-sig] Asynchronous cleanup is a problem

[David Beazley]

Cory wrote:

"What’s not entirely clear to me is why we need __aexit__ to *actually* be an async function. The example in curio is socket closure, which seems to be like it absolutely does not need to be awaitable."

Curio uses asynchronous context managers for much more than closing sockets (which frankly is the least interesting thing).   For example, they're used extensively with synchronization primitives such as Locks, Semaphores, Events, Queues, and other such things.   The ability to use coroutines in the __aexit__() method is an essential part of these primitives because it allows task scheduling decisions to be made in conjunction with synchronization events such as lock releases.   For example, you can implement fair-locking or various forms of priority scheduling.   Curio also uses asynchronous context managers for timeouts and other related functionality where coroutines have to be used in __aexit__.  I would expect coroutines in __aexit__ to also be useful in more advanced contexts such as working with databases, dealing with transactions, and other kinds of processing where asynchronous I/O might be involved.

As such, I think it's pretty useful to allow coroutines in __aexit__() and would be strongly opposed to restricting it.

-Dave