Deadlocks In ParAff / Kills

[eric-corumdigital]

There are several cases where deadlocks will occur if a Queue is used in any Fiber which is killed (ParAff is a common scenario).

read ∷ ∀ a. Queue a → Aff a
read (Queue q) = do
  readEnd ← AVar.take q.readEnd
  // Kill here leaves readEnd empty
  QItem a newRead ← AVar.read readEnd
  AVar.put newRead q.readEnd
  pure a

Invincibility is not a solution because that will lead to external deadlock problems. I have been long down this road with Aff, and even patched the library to fix a critical temporal issue that will also be at play here. When I am able to share the fix I will.

[safareli]

@eric-corumdigital with your recent work on Aff is it (or will it be) possible to fix this issues like this?

[safareli]

I think this can be fixed using similar approach taken here and this is what's used under the hood.

[eric-corumdigital]

I made my own implementation. The temporal kills fix allows you to use brackets properly, which in turn allows these sorts of issues to be resolved.

The implementation I am using now is just an AVar. Writing is launching a Fiber which puts to the AVar. Reading is taking from the AVar. Really simple.

[safareli]

The temporal kills fix allows you to use brackets properly, which in turn allows these sorts of issues to be resolved.

It would be great if you can you provide an example of how bracket with the fix can solve this issue.
Thanks!