{-# OPTIONS_GHC -fno-implicit-prelude #-}
--------------------------------------------------------------------------------
-- |
-- Module      :  Foreign.Marshal.Pool
-- Copyright   :  (c) Sven Panne 2002-2004
-- License     :  BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer  :  sven.panne@aedion.de
-- Stability   :  provisional
-- Portability :  portable
--
-- This module contains support for pooled memory management. Under this scheme,
-- (re-)allocations belong to a given pool, and everything in a pool is
-- deallocated when the pool itself is deallocated. This is useful when
-- 'Foreign.Marshal.Alloc.alloca' with its implicit allocation and deallocation
-- is not flexible enough, but explicit uses of 'Foreign.Marshal.Alloc.malloc'
-- and 'free' are too awkward.
--
--------------------------------------------------------------------------------

module Foreign.Marshal.Pool (
   -- * Pool management
   Pool,
   newPool,             -- :: IO Pool
   freePool,            -- :: Pool -> IO ()
   withPool,            -- :: (Pool -> IO b) -> IO b

   -- * (Re-)Allocation within a pool
   pooledMalloc,        -- :: Storable a => Pool                 -> IO (Ptr a)
   pooledMallocBytes,   -- ::               Pool          -> Int -> IO (Ptr a)

   pooledRealloc,       -- :: Storable a => Pool -> Ptr a        -> IO (Ptr a)
   pooledReallocBytes,  -- ::               Pool -> Ptr a -> Int -> IO (Ptr a)

   pooledMallocArray,   -- :: Storable a => Pool ->          Int -> IO (Ptr a)
   pooledMallocArray0,  -- :: Storable a => Pool ->          Int -> IO (Ptr a)

   pooledReallocArray,  -- :: Storable a => Pool -> Ptr a -> Int -> IO (Ptr a)
   pooledReallocArray0, -- :: Storable a => Pool -> Ptr a -> Int -> IO (Ptr a)

   -- * Combined allocation and marshalling
   pooledNew,           -- :: Storable a => Pool -> a            -> IO (Ptr a)
   pooledNewArray,      -- :: Storable a => Pool ->      [a]     -> IO (Ptr a)
   pooledNewArray0      -- :: Storable a => Pool -> a -> [a]     -> IO (Ptr a)
) where

import Data.IORef            ( IORef, newIORef, readIORef, writeIORef )

import Control.Exception     ( bracket )

import Control.Monad         ( liftM )
import Data.List             ( delete )
import Foreign.Marshal.Alloc ( mallocBytes, reallocBytes, free )
import Foreign.Marshal.Array ( pokeArray, pokeArray0 )
import Foreign.Marshal.Error ( throwIf )
import Foreign.Ptr           ( Ptr, castPtr )
import Foreign.Storable      ( Storable(sizeOf, poke) )

--------------------------------------------------------------------------------

-- To avoid non-H98 stuff like existentially quantified data constructors, we
-- simply use pointers to () below. Not very nice, but...

-- | A memory pool.

newtype Pool = Pool (IORef [Ptr ()])

-- | Allocate a fresh memory pool.

newPool :: IO Pool
newPool = liftM Pool (newIORef [])

-- | Deallocate a memory pool and everything which has been allocated in the
-- pool itself.

freePool :: Pool -> IO ()
freePool (Pool pool) = readIORef pool >>= freeAll
   where freeAll []     = return ()
         freeAll (p:ps) = free p >> freeAll ps

-- | Execute an action with a fresh memory pool, which gets automatically
-- deallocated (including its contents) after the action has finished.

withPool :: (Pool -> IO b) -> IO b
withPool = bracket newPool freePool

--------------------------------------------------------------------------------

-- | Allocate space for storable type in the given pool. The size of the area
-- allocated is determined by the 'sizeOf' method from the instance of
-- 'Storable' for the appropriate type.

pooledMalloc :: Storable a => Pool -> IO (Ptr a)
pooledMalloc = pm undefined
  where
    pm           :: Storable a' => a' -> Pool -> IO (Ptr a')
    pm dummy pool = pooledMallocBytes pool (sizeOf dummy)

-- | Allocate the given number of bytes of storage in the pool.

pooledMallocBytes :: Pool -> Int -> IO (Ptr a)
pooledMallocBytes (Pool pool) size = do
   ptr <- mallocBytes size
   ptrs <- readIORef pool
   writeIORef pool (ptr:ptrs)
   return (castPtr ptr)

-- | Adjust the storage area for an element in the pool to the given size of
-- the required type.

pooledRealloc :: Storable a => Pool -> Ptr a -> IO (Ptr a)
pooledRealloc = pr undefined
  where
    pr               :: Storable a' => a' -> Pool -> Ptr a' -> IO (Ptr a')
    pr dummy pool ptr = pooledReallocBytes pool ptr (sizeOf dummy)

-- | Adjust the storage area for an element in the pool to the given size.

pooledReallocBytes :: Pool -> Ptr a -> Int -> IO (Ptr a)
pooledReallocBytes (Pool pool) ptr size = do
   let cPtr = castPtr ptr
   throwIf (not . (cPtr `elem`)) (\_ -> "pointer not in pool") (readIORef pool)
   newPtr <- reallocBytes cPtr size
   ptrs <- readIORef pool
   writeIORef pool (newPtr : delete cPtr ptrs)
   return (castPtr newPtr)

-- | Allocate storage for the given number of elements of a storable type in the
-- pool.

pooledMallocArray :: Storable a => Pool -> Int -> IO (Ptr a)
pooledMallocArray = pma undefined
  where
    pma                :: Storable a' => a' -> Pool -> Int -> IO (Ptr a')
    pma dummy pool size = pooledMallocBytes pool (size * sizeOf dummy)

-- | Allocate storage for the given number of elements of a storable type in the
-- pool, but leave room for an extra element to signal the end of the array.

pooledMallocArray0 :: Storable a => Pool -> Int -> IO (Ptr a)
pooledMallocArray0 pool size =
   pooledMallocArray pool (size + 1)

-- | Adjust the size of an array in the given pool.

pooledReallocArray :: Storable a => Pool -> Ptr a -> Int -> IO (Ptr a)
pooledReallocArray = pra undefined
  where
    pra                ::  Storable a' => a' -> Pool -> Ptr a' -> Int -> IO (Ptr a')
    pra dummy pool ptr size  = pooledReallocBytes pool ptr (size * sizeOf dummy)

-- | Adjust the size of an array with an end marker in the given pool.

pooledReallocArray0 :: Storable a => Pool -> Ptr a -> Int -> IO (Ptr a)
pooledReallocArray0 pool ptr size =
   pooledReallocArray pool ptr (size + 1)

--------------------------------------------------------------------------------

-- | Allocate storage for a value in the given pool and marshal the value into
-- this storage.

pooledNew :: Storable a => Pool -> a -> IO (Ptr a)
pooledNew pool val = do
   ptr <- pooledMalloc pool
   poke ptr val
   return ptr

-- | Allocate consecutive storage for a list of values in the given pool and
-- marshal these values into it.

pooledNewArray :: Storable a => Pool -> [a] -> IO (Ptr a)
pooledNewArray pool vals = do
   ptr <- pooledMallocArray pool (length vals)
   pokeArray ptr vals
   return ptr

-- | Allocate consecutive storage for a list of values in the given pool and
-- marshal these values into it, terminating the end with the given marker.

pooledNewArray0 :: Storable a => Pool -> a -> [a] -> IO (Ptr a)
pooledNewArray0 pool marker vals = do
   ptr <- pooledMallocArray0 pool (length vals)
   pokeArray0 marker ptr vals
   return ptr
