Data.Acquire.Internal

A method for acquiring a scarce resource, providing the means of freeing it when no longer needed. This data type provides Functor/Applicative/Monad instances for composing different resources together. You can allocate these resources using either the bracket pattern (via with) or using ResourceT (via allocateAcquire).

This concept was originally introduced by Gabriel Gonzalez and described at: http://www.haskellforall.com/2013/06/the-resource-applicative.html. The implementation in this package is slightly different, due to taking a different approach to async exception safety.

Allocate the given resource and provide it to the provided function. The resource will be freed as soon as the inner block is exited, whether normally or via an exception. This function is similar in function to bracket.

Create an Acquire value using the given allocate and free functions.

To acquire and free the resource in an arbitrary monad with MonadUnliftIO, do the following:

acquire <- withRunInIO $ \runInIO ->
  return $ mkAcquire (runInIO create) (runInIO . free)

Note that this is only safe if the Acquire is run and freed within the same monadic scope it was created in.

The way in which a release is called.

Same as mkAcquire, but the cleanup function will be informed of how cleanup was initiated. This allows you to distinguish, for example, between normal and exceptional exits.

To acquire and free the resource in an arbitrary monad with MonadUnliftIO, do the following:

acquire <- withRunInIO $ \runInIO ->
  return $ mkAcquireType (runInIO create) (\a -> runInIO . free a)

Note that this is only safe if the Acquire is run and freed within the same monadic scope it was created in.