Add `Lock` to std

[armanbilge]

Spinning out of #3480 (comment).

The API would look something like:

abstract class Lock[F[_]] {
  def shared: Resource[F, Unit]
  def exclusive: Resource[F, Unit]
}

[ChristopherDavenport]

https://github.com/davenverse/lock - Available as some prior art.

[djspiewak]

…with the caveat that we can only implement reentrancy for IO, not for general effect types, since reentrancy requires some form of fiber identity (which we can access using IOLocal).

[kevchuang]

Hi, I would like to help on this issue !

[sebastianrozyczka]

Hi @armanbilge, I can try to approach this one if it's still valid :) Could we just summarize how we would like the Lock API to be shaped?

[armanbilge]

hi @sebastianrozyczka, that's great, thank you! Have you had a chance to look at this old PR?

• Add Lock to std #3542

You can use that branch to start your own PR. Please review the code and comments in the PR and let us know if you have questions :)

[sebastianrozyczka]

@armanbilge Actually yes, if what is mentioned in the comments is enough for us then I guess I have no questions, thanks a lot! I will let you know as soon as I have something. :)