https://discourse.haskell.org/t/how-to-write-a-proper-forking-bracket-function/1012/2

bracket-fork.hs

import Control.Exception.Safe
import Control.Concurrent

bracketFork
    :: IO resource
        -- ^ The first action; will run in the current thread
    -> (resource -> IO a)
        -- ^ A final action that runs in the forked thread, with async exceptions masked
    -> (resource -> IO b)
        -- ^ Action that runs in the forked thread, with async exceptions unmasked
    -> IO ThreadId

bracketFork open close action =
    mask_ $
      do
        resource <- open
        action resource `forkUnmaskedFinally` close resource

forkUnmaskedFinally
    :: IO a
        -- ^ Action that runs in the forked thread, with async exceptions unmasked
    -> IO b
        -- ^ A final action that runs in the forked thread, with async exceptions masked
    -> IO ThreadId

forkUnmaskedFinally action close =
    mask_ $ forkIOWithUnmask $ \unmask ->
      do
        unmask action `onException` close
        close
        return ()