content: {-# LANGUAGE Unsafe #-}
  {-# LANGUAGE CPP
             , NoImplicitPrelude
             , BangPatterns
             , MagicHash
             , UnboxedTuples
    #-}
  {-# OPTIONS_HADDOCK hide #-}
  {-# LANGUAGE DeriveDataTypeable, StandaloneDeriving #-}
  
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  GHC.ForeignPtr
  -- Copyright   :  (c) The University of Glasgow, 1992-2003
  -- License     :  see libraries/base/LICENSE
  -- 
  -- Maintainer  :  cvs-ghc@haskell.org
  -- Stability   :  internal
  -- Portability :  non-portable (GHC extensions)
  --
  -- GHC's implementation of the 'ForeignPtr' data type.
  -- 
  -----------------------------------------------------------------------------
  
  -- #hide
  module GHC.ForeignPtr
    (
          ForeignPtr(..),
          FinalizerPtr,
          FinalizerEnvPtr,
          newForeignPtr_,
          mallocForeignPtr,
          mallocPlainForeignPtr,
          mallocForeignPtrBytes,
          mallocPlainForeignPtrBytes,
          addForeignPtrFinalizer,
          addForeignPtrFinalizerEnv,
          touchForeignPtr,
          unsafeForeignPtrToPtr,
          castForeignPtr,
          newConcForeignPtr,
          addForeignPtrConcFinalizer,
          finalizeForeignPtr
    ) where
  
  import Control.Monad    ( sequence_ )
  import Foreign.Storable
  import Data.Typeable
  
  import GHC.Show
  import GHC.List         ( null )
  import GHC.Base
  import GHC.IORef
  import GHC.STRef        ( STRef(..) )
  import GHC.Ptr          ( Ptr(..), FunPtr(..) )
  import GHC.Err
  
  #include "Typeable.h"
  
  -- |The type 'ForeignPtr' represents references to objects that are
  -- maintained in a foreign language, i.e., that are not part of the
  -- data structures usually managed by the Haskell storage manager.
  -- The essential difference between 'ForeignPtr's and vanilla memory
  -- references of type @Ptr a@ is that the former may be associated
  -- with /finalizers/. A finalizer is a routine that is invoked when
  -- the Haskell storage manager detects that - within the Haskell heap
  -- and stack - there are no more references left that are pointing to
  -- the 'ForeignPtr'.  Typically, the finalizer will, then, invoke
  -- routines in the foreign language that free the resources bound by
  -- the foreign object.
  --
  -- The 'ForeignPtr' is parameterised in the same way as 'Ptr'.  The
  -- type argument of 'ForeignPtr' should normally be an instance of
  -- class 'Storable'.
  --
  data ForeignPtr a = ForeignPtr Addr# ForeignPtrContents
          -- we cache the Addr# in the ForeignPtr object, but attach
          -- the finalizer to the IORef (or the MutableByteArray# in
          -- the case of a MallocPtr).  The aim of the representation
          -- is to make withForeignPtr efficient; in fact, withForeignPtr
          -- should be just as efficient as unpacking a Ptr, and multiple
          -- withForeignPtrs can share an unpacked ForeignPtr.  Note
          -- that touchForeignPtr only has to touch the ForeignPtrContents
          -- object, because that ensures that whatever the finalizer is
          -- attached to is kept alive.
  
  INSTANCE_TYPEABLE1(ForeignPtr,foreignPtrTc,"ForeignPtr")
  
  data Finalizers
    = NoFinalizers
    | CFinalizers
    | HaskellFinalizers
      deriving Eq
  
  data ForeignPtrContents
    = PlainForeignPtr !(IORef (Finalizers, [IO ()]))
    | MallocPtr      (MutableByteArray# RealWorld) !(IORef (Finalizers, [IO ()]))
    | PlainPtr       (MutableByteArray# RealWorld)
  
  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)
  
  
  -- |A finalizer is represented as a pointer to a foreign function that, at
  -- finalisation time, gets as an argument a plain pointer variant of the
  -- foreign pointer that the finalizer is associated with.
  -- 
  type FinalizerPtr a        = FunPtr (Ptr a -> IO ())
  type FinalizerEnvPtr env a = FunPtr (Ptr env -> Ptr a -> IO ())
  
  newConcForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a)
  --
  -- ^Turns a plain memory reference into a foreign object by
  -- associating a finalizer - given by the monadic operation - with the
  -- reference.  The storage manager will start the finalizer, in a
  -- separate thread, some time after the last reference to the
  -- @ForeignPtr@ is dropped.  There is no guarantee of promptness, and
  -- in fact there is no guarantee that the finalizer will eventually
  -- run at all.
  --
  -- Note that references from a finalizer do not necessarily prevent
  -- another object from being finalized.  If A's finalizer refers to B
  -- (perhaps using 'touchForeignPtr', then the only guarantee is that
  -- B's finalizer will never be started before A's.  If both A and B
  -- are unreachable, then both finalizers will start together.  See
  -- 'touchForeignPtr' for more on finalizer ordering.
  --
  newConcForeignPtr p finalizer
    = do fObj <- newForeignPtr_ p
         addForeignPtrConcFinalizer fObj finalizer
         return fObj
  
  mallocForeignPtr :: Storable a => IO (ForeignPtr a)
  -- ^ Allocate some memory and return a 'ForeignPtr' to it.  The memory
  -- will be released automatically when the 'ForeignPtr' is discarded.
  --
  -- 'mallocForeignPtr' is equivalent to
  --
  -- >    do { p <- malloc; newForeignPtr finalizerFree p }
  -- 
  -- although it may be implemented differently internally: you may not
  -- assume that the memory returned by 'mallocForeignPtr' has been
  -- allocated with 'Foreign.Marshal.Alloc.malloc'.
  --
  -- GHC notes: 'mallocForeignPtr' has a heavily optimised
  -- implementation in GHC.  It uses pinned memory in the garbage
  -- collected heap, so the 'ForeignPtr' does not require a finalizer to
  -- free the memory.  Use of 'mallocForeignPtr' and associated
  -- functions is strongly recommended in preference to 'newForeignPtr'
  -- with a finalizer.
  -- 
  mallocForeignPtr = doMalloc undefined
    where doMalloc :: Storable b => b -> IO (ForeignPtr b)
          doMalloc a
            | I# size < 0 = error "mallocForeignPtr: size must be >= 0"
            | otherwise = do
            r <- newIORef (NoFinalizers, [])
            IO $ \s ->
              case newAlignedPinnedByteArray# size align s of { (# s', mbarr# #) ->
               (# s', ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
                                 (MallocPtr mbarr# r) #)
              }
              where !(I# size)  = sizeOf a
                    !(I# align) = alignment a
  
  -- | This function is similar to 'mallocForeignPtr', except that the
  -- size of the memory required is given explicitly as a number of bytes.
  mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
  mallocForeignPtrBytes size | size < 0 =
    error "mallocForeignPtrBytes: size must be >= 0"
  mallocForeignPtrBytes (I# size) = do 
    r <- newIORef (NoFinalizers, [])
    IO $ \s ->
       case newPinnedByteArray# size s      of { (# s', mbarr# #) ->
         (# s', ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
                           (MallocPtr mbarr# r) #)
       }
  
  -- | Allocate some memory and return a 'ForeignPtr' to it.  The memory
  -- will be released automatically when the 'ForeignPtr' is discarded.
  --
  -- GHC notes: 'mallocPlainForeignPtr' has a heavily optimised
  -- implementation in GHC.  It uses pinned memory in the garbage
  -- collected heap, as for mallocForeignPtr. Unlike mallocForeignPtr, a
  -- ForeignPtr created with mallocPlainForeignPtr carries no finalizers.
  -- It is not possible to add a finalizer to a ForeignPtr created with
  -- mallocPlainForeignPtr. This is useful for ForeignPtrs that will live
  -- only inside Haskell (such as those created for packed strings).
  -- Attempts to add a finalizer to a ForeignPtr created this way, or to
  -- finalize such a pointer, will throw an exception.
  -- 
  mallocPlainForeignPtr :: Storable a => IO (ForeignPtr a)
  mallocPlainForeignPtr = doMalloc undefined
    where doMalloc :: Storable b => b -> IO (ForeignPtr b)
          doMalloc a
            | I# size < 0 = error "mallocForeignPtr: size must be >= 0"
            | otherwise = IO $ \s ->
              case newAlignedPinnedByteArray# size align s of { (# s', mbarr# #) ->
               (# s', ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
                                 (PlainPtr mbarr#) #)
              }
              where !(I# size)  = sizeOf a
                    !(I# align) = alignment a
  
  -- | This function is similar to 'mallocForeignPtrBytes', except that
  -- the internally an optimised ForeignPtr representation with no
  -- finalizer is used. Attempts to add a finalizer will cause an
  -- exception to be thrown.
  mallocPlainForeignPtrBytes :: Int -> IO (ForeignPtr a)
  mallocPlainForeignPtrBytes size | size < 0 =
    error "mallocPlainForeignPtrBytes: size must be >= 0"
  mallocPlainForeignPtrBytes (I# size) = IO $ \s ->
      case newPinnedByteArray# size s      of { (# s', mbarr# #) ->
         (# s', ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
                           (PlainPtr mbarr#) #)
       }
  
  addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO ()
  -- ^This function adds a finalizer to the given foreign object.  The
  -- finalizer will run /before/ all other finalizers for the same
  -- object which have already been registered.
  addForeignPtrFinalizer (FunPtr fp) (ForeignPtr p c) = case c of
    PlainForeignPtr r -> f r >> return ()
    MallocPtr     _ r -> f r >> return ()
    _ -> error "GHC.ForeignPtr: attempt to add a finalizer to a plain pointer"
   where
      f r =
        noMixing CFinalizers r $
          IO $ \s ->
            case r of { IORef (STRef r#) ->
            case mkWeakForeignEnv# r# () fp p 0# nullAddr# s of { (# s1, w #) ->
            (# s1, finalizeForeign w #) }}
  
  addForeignPtrFinalizerEnv ::
    FinalizerEnvPtr env a -> Ptr env -> ForeignPtr a -> IO ()
  -- ^ Like 'addForeignPtrFinalizerEnv' but allows the finalizer to be
  -- passed an additional environment parameter to be passed to the
  -- finalizer.  The environment passed to the finalizer is fixed by the
  -- second argument to 'addForeignPtrFinalizerEnv'
  addForeignPtrFinalizerEnv (FunPtr fp) (Ptr ep) (ForeignPtr p c) = case c of
    PlainForeignPtr r -> f r >> return ()
    MallocPtr     _ r -> f r >> return ()
    _ -> error "GHC.ForeignPtr: attempt to add a finalizer to a plain pointer"
   where
      f r =
        noMixing CFinalizers r $
          IO $ \s ->
            case r of { IORef (STRef r#) ->
            case mkWeakForeignEnv# r# () fp p 1# ep s of { (# s1, w #) ->
            (# s1, finalizeForeign w #) }}
  
  finalizeForeign :: Weak# () -> IO ()
  finalizeForeign w = IO $ \s ->
    case finalizeWeak# w s of
      (# s1, 0#, _ #) -> (# s1, () #)
      (# s1, _ , f #) -> f s1
  
  addForeignPtrConcFinalizer :: ForeignPtr a -> IO () -> IO ()
  -- ^This function adds a finalizer to the given @ForeignPtr@.  The
  -- finalizer will run /before/ all other finalizers for the same
  -- object which have already been registered.
  --
  -- This is a variant of @addForeignPtrFinalizer@, where the finalizer
  -- is an arbitrary @IO@ action.  When it is invoked, the finalizer
  -- will run in a new thread.
  --
  -- NB. Be very careful with these finalizers.  One common trap is that
  -- if a finalizer references another finalized value, it does not
  -- prevent that value from being finalized.  In particular, 'Handle's
  -- are finalized objects, so a finalizer should not refer to a 'Handle'
  -- (including @stdout@, @stdin@ or @stderr@).
  --
  addForeignPtrConcFinalizer (ForeignPtr _ c) finalizer = 
    addForeignPtrConcFinalizer_ c finalizer
  
  addForeignPtrConcFinalizer_ :: ForeignPtrContents -> IO () -> IO ()
  addForeignPtrConcFinalizer_ (PlainForeignPtr r) finalizer = do
    noFinalizers <- noMixing HaskellFinalizers r (return finalizer)
    if noFinalizers
       then IO $ \s ->
                case r of { IORef (STRef r#) ->
                case mkWeak# r# () (foreignPtrFinalizer r) s of {  (# s1, _ #) ->
                (# s1, () #) }}
       else return ()
  addForeignPtrConcFinalizer_ f@(MallocPtr fo r) finalizer = do
    noFinalizers <- noMixing HaskellFinalizers r (return finalizer)
    if noFinalizers
       then  IO $ \s -> 
                 case mkWeak# fo () (do foreignPtrFinalizer r; touch f) s of
                    (# s1, _ #) -> (# s1, () #)
       else return ()
  
  addForeignPtrConcFinalizer_ _ _ =
    error "GHC.ForeignPtr: attempt to add a finalizer to plain pointer"
  
  noMixing ::
    Finalizers -> IORef (Finalizers, [IO ()]) -> IO (IO ()) -> IO Bool
  noMixing ftype0 r mkF = do
    (ftype, fs) <- readIORef r
    if ftype /= NoFinalizers && ftype /= ftype0
       then error ("GHC.ForeignPtr: attempt to mix Haskell and C finalizers " ++
                   "in the same ForeignPtr")
       else do
         f <- mkF
         writeIORef r (ftype0, f : fs)
         return (null fs)
  
  foreignPtrFinalizer :: IORef (Finalizers, [IO ()]) -> IO ()
  foreignPtrFinalizer r = do (_, fs) <- readIORef r; sequence_ fs
  
  newForeignPtr_ :: Ptr a -> IO (ForeignPtr a)
  -- ^Turns a plain memory reference into a foreign pointer that may be
  -- associated with finalizers by using 'addForeignPtrFinalizer'.
  newForeignPtr_ (Ptr obj) =  do
    r <- newIORef (NoFinalizers, [])
    return (ForeignPtr obj (PlainForeignPtr r))
  
  touchForeignPtr :: ForeignPtr a -> IO ()
  -- ^This function ensures that the foreign object in
  -- question is alive at the given place in the sequence of IO
  -- actions. In particular 'Foreign.ForeignPtr.withForeignPtr'
  -- does a 'touchForeignPtr' after it
  -- executes the user action.
  -- 
  -- Note that this function should not be used to express dependencies
  -- between finalizers on 'ForeignPtr's.  For example, if the finalizer
  -- for a 'ForeignPtr' @F1@ calls 'touchForeignPtr' on a second
  -- 'ForeignPtr' @F2@, then the only guarantee is that the finalizer
  -- for @F2@ is never started before the finalizer for @F1@.  They
  -- might be started together if for example both @F1@ and @F2@ are
  -- otherwise unreachable, and in that case the scheduler might end up
  -- running the finalizer for @F2@ first.
  --
  -- In general, it is not recommended to use finalizers on separate
  -- objects with ordering constraints between them.  To express the
  -- ordering robustly requires explicit synchronisation using @MVar@s
  -- between the finalizers, but even then the runtime sometimes runs
  -- multiple finalizers sequentially in a single thread (for
  -- performance reasons), so synchronisation between finalizers could
  -- result in artificial deadlock.  Another alternative is to use
  -- explicit reference counting.
  --
  touchForeignPtr (ForeignPtr _ r) = touch r
  
  touch :: ForeignPtrContents -> IO ()
  touch r = IO $ \s -> case touch# r s of s' -> (# s', () #)
  
  unsafeForeignPtrToPtr :: ForeignPtr a -> Ptr a
  -- ^This function extracts the pointer component of a foreign
  -- pointer.  This is a potentially dangerous operations, as if the
  -- argument to 'unsafeForeignPtrToPtr' is the last usage
  -- occurrence of the given foreign pointer, then its finalizer(s) will
  -- be run, which potentially invalidates the plain pointer just
  -- obtained.  Hence, 'touchForeignPtr' must be used
  -- wherever it has to be guaranteed that the pointer lives on - i.e.,
  -- has another usage occurrence.
  --
  -- To avoid subtle coding errors, hand written marshalling code
  -- should preferably use 'Foreign.ForeignPtr.withForeignPtr' rather
  -- than combinations of 'unsafeForeignPtrToPtr' and
  -- 'touchForeignPtr'.  However, the latter routines
  -- are occasionally preferred in tool generated marshalling code.
  unsafeForeignPtrToPtr (ForeignPtr fo _) = Ptr fo
  
  castForeignPtr :: ForeignPtr a -> ForeignPtr b
  -- ^This function casts a 'ForeignPtr'
  -- parameterised by one type into another type.
  castForeignPtr f = unsafeCoerce# f
  
  -- | Causes the finalizers associated with a foreign pointer to be run
  -- immediately.
  finalizeForeignPtr :: ForeignPtr a -> IO ()
  finalizeForeignPtr (ForeignPtr _ (PlainPtr _)) = return () -- no effect
  finalizeForeignPtr (ForeignPtr _ foreignPtr) = do
          (ftype, finalizers) <- readIORef refFinalizers
          sequence_ finalizers
          writeIORef refFinalizers (ftype, [])
          where
                  refFinalizers = case foreignPtr of
                          (PlainForeignPtr ref) -> ref
                          (MallocPtr     _ ref) -> ref
                          PlainPtr _            ->
                              error "finalizeForeignPtr PlainPtr"
  
  