chepiov / cats-effect-miscellaneous Goto Github PK

WorkerPool

I like your implementation with versions, however, exec not safe wrt cancellation:

for {
  (workerVersion, worker) <- current.take
  // [X]
  currentVersion          <- version.get
  // [Y]
  b <- if (currentVersion == workerVersion)
         worker(a).guarantee(back(workerVersion, worker))
       else exec(a)
} yield b

Because of cancelable flatMaps, it's possible for cancellation to happen at [X] or [Y], in which case you leak the worker (as it's never returned to the MVar, even if I didn't do removeAll).

You can fix it using uncancelable, but you don't want to make everything uncancelable. bracket would work too (acquire and release parts of bracket are uncancelable), but looping and de-structuring would be painful.

Race

It seems (from the code) that you're building a tree of CompositeExceptions with prepend, i.e.

CompositeException(
  throwable1,
  CompositeException(
    throwable2,
    CompositeException(
      ...
    )
  )
)

It also seems that your getMessage override would not discriminate between these cases :) Ideally, you'd want to somehow ensure you work with CompositeException instead of Throwable, which you can safely combine together.

Custom extractors are a nice touch, but there's also an option to avoid matching on two cases: Either has merge method, which can only be called if left and right have (potential) same type. So, you can do something like either.leftMap(_.swap).merge to get (Fiber[...], Either[...]).

And if it all seems like nitpicking, that's because there's not really anything significant for me to complain about. Nice solutions, and congratulations 👍