{-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Foreign.ForeignPtr
-- Copyright   :  (c) The University of Glasgow 2001
-- License     :  BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer  :  ffi@haskell.org
-- Stability   :  provisional
-- Portability :  portable
--
-- The 'ForeignPtr' type and operations.  This module is part of the
-- Foreign Function Interface (FFI) and will usually be imported via
-- the "Foreign" module.
--
-----------------------------------------------------------------------------

module Foreign.ForeignPtr
        ( 
	-- * Finalised data pointers
	  ForeignPtr
	, FinalizerPtr

	, FinalizerEnvPtr

	-- ** Basic operations
        , newForeignPtr
        , newForeignPtr_
        , addForeignPtrFinalizer

	, newForeignPtrEnv
	, addForeignPtrFinalizerEnv

	, withForeignPtr

	-- ** Low-level operations
	, unsafeForeignPtrToPtr
	, touchForeignPtr
	, castForeignPtr

	-- ** Allocating managed memory
	, mallocForeignPtr
	, mallocForeignPtrBytes
	, mallocForeignPtrArray
	, mallocForeignPtrArray0
        ) 
	where

import Foreign.Ptr

import Hugs.ForeignPtr

import Foreign.Storable	( Storable(sizeOf) )

import Foreign.Marshal.Alloc	( malloc, mallocBytes, finalizerFree )

instance Eq (ForeignPtr a) where 
    p == q  =  unsafeForeignPtrToPtr p == unsafeForeignPtrToPtr q

instance Ord (ForeignPtr a) where 
    compare p q  =  compare (unsafeForeignPtrToPtr p) (unsafeForeignPtrToPtr q)

instance Show (ForeignPtr a) where
    showsPrec p f = showsPrec p (unsafeForeignPtrToPtr f)

newForeignPtr :: FinalizerPtr a -> Ptr a -> IO (ForeignPtr a)
-- ^Turns a plain memory reference into a foreign pointer, and
-- associates a finaliser with the reference.  The finaliser will be executed
-- after the last reference to the foreign object is dropped.  Note that there
-- is no guarantee on how soon the finaliser is executed after the last
-- reference was dropped; this depends on the details of the Haskell storage
-- manager. The only guarantee is that the finaliser runs before the program
-- terminates.
newForeignPtr finalizer p
  = do fObj <- newForeignPtr_ p
       addForeignPtrFinalizer finalizer fObj
       return fObj

withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b
-- ^This is a way to look at the pointer living inside a
-- foreign object.  This function takes a function which is
-- applied to that pointer. The resulting 'IO' action is then
-- executed. The foreign object is kept alive at least during
-- the whole action, even if it is not used directly
-- inside. Note that it is not safe to return the pointer from
-- the action and use it after the action completes. All uses
-- of the pointer should be inside the
-- 'withForeignPtr' bracket.  The reason for
-- this unsafeness is the same as for
-- 'unsafeForeignPtrToPtr' below: the finalizer
-- may run earlier than expected, because the compiler can only
-- track usage of the 'ForeignPtr' object, not
-- a 'Ptr' object made from it.
--
-- This function is normally used for marshalling data to
-- or from the object pointed to by the
-- 'ForeignPtr', using the operations from the
-- 'Storable' class.
withForeignPtr fo io
  = do r <- io (unsafeForeignPtrToPtr fo)
       touchForeignPtr fo
       return r

-- | This variant of 'newForeignPtr' adds a finalizer that expects an
-- environment in addition to the finalized pointer.  The environment
-- that will be passed to the finalizer is fixed by the second argument to
-- 'newForeignPtrEnv'.
newForeignPtrEnv ::
    FinalizerEnvPtr env a -> Ptr env -> Ptr a -> IO (ForeignPtr a)
newForeignPtrEnv finalizer env p
  = do fObj <- newForeignPtr_ p
       addForeignPtrFinalizerEnv finalizer env fObj
       return fObj

mallocForeignPtr :: Storable a => IO (ForeignPtr a)
mallocForeignPtr = do
  r <- malloc
  newForeignPtr finalizerFree r

mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
mallocForeignPtrBytes n = do
  r <- mallocBytes n
  newForeignPtr finalizerFree r

-- | This function is similar to 'Foreign.Marshal.Array.mallocArray',
-- but yields a memory area that has a finalizer attached that releases
-- the memory area.  As with 'mallocForeignPtr', it is not guaranteed that
-- the block of memory was allocated by 'Foreign.Marshal.Alloc.malloc'.
mallocForeignPtrArray :: Storable a => Int -> IO (ForeignPtr a)
mallocForeignPtrArray  = doMalloc undefined
  where
    doMalloc            :: Storable b => b -> Int -> IO (ForeignPtr b)
    doMalloc dummy size  = mallocForeignPtrBytes (size * sizeOf dummy)

-- | This function is similar to 'Foreign.Marshal.Array.mallocArray0',
-- but yields a memory area that has a finalizer attached that releases
-- the memory area.  As with 'mallocForeignPtr', it is not guaranteed that
-- the block of memory was allocated by 'Foreign.Marshal.Alloc.malloc'.
mallocForeignPtrArray0      :: Storable a => Int -> IO (ForeignPtr a)
mallocForeignPtrArray0 size  = mallocForeignPtrArray (size + 1)
