-{-# OPTIONS_GHC -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
+{-# OPTIONS_HADDOCK hide #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.ForeignPtr
--
-----------------------------------------------------------------------------
+-- #hide
module GHC.ForeignPtr
(
- ForeignPtr(..),
- FinalizerPtr,
- newForeignPtr_,
- mallocForeignPtr,
- mallocForeignPtrBytes,
- addForeignPtrFinalizer,
- touchForeignPtr,
- unsafeForeignPtrToPtr,
- castForeignPtr,
- newConcForeignPtr,
- addForeignPtrConcFinalizer,
- finalizeForeignPtr
+ ForeignPtr(..),
+ FinalizerPtr,
+ FinalizerEnvPtr,
+ newForeignPtr_,
+ mallocForeignPtr,
+ mallocPlainForeignPtr,
+ mallocForeignPtrBytes,
+ mallocPlainForeignPtrBytes,
+ addForeignPtrFinalizer,
+ addForeignPtrFinalizerEnv,
+ touchForeignPtr,
+ unsafeForeignPtrToPtr,
+ castForeignPtr,
+ newConcForeignPtr,
+ addForeignPtrConcFinalizer,
+ finalizeForeignPtr
) where
-import Control.Monad ( sequence_ )
-import Foreign.Ptr
+import Control.Monad ( sequence_ )
import Foreign.Storable
+import Data.Typeable
-import GHC.List ( null )
+import GHC.Show
+import GHC.List ( null )
import GHC.Base
-import GHC.IOBase
-import GHC.Ptr ( Ptr(..) )
+import GHC.IORef
+import GHC.STRef ( STRef(..) )
+import GHC.Ptr ( Ptr(..), FunPtr(..) )
import GHC.Err
-import GHC.Show
+import GHC.Num ( fromInteger )
+
+#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
-- type argument of 'ForeignPtr' should normally be an instance of
-- class 'Storable'.
--
-data ForeignPtr a
- = ForeignPtr ForeignObj# !(IORef [IO ()])
- | MallocPtr (MutableByteArray# RealWorld) !(IORef [IO ()])
+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 Show (ForeignPtr a) where
showsPrec p f = showsPrec p (unsafeForeignPtrToPtr f)
--- |A Finalizer is represented as a pointer to a foreign function that, at
+
+-- |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 FinalizerPtr a = FunPtr (Ptr a -> IO ())
+type FinalizerEnvPtr env a = FunPtr (Ptr env -> Ptr a -> IO ())
newConcForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a)
--
-- 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
-- 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 = do
- r <- newIORef []
- IO $ \s ->
- case newPinnedByteArray# size s of { (# s, mbarr# #) ->
- (# s, MallocPtr mbarr# r #)
+ 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
+ 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 []
+ r <- newIORef (NoFinalizers, [])
IO $ \s ->
- case newPinnedByteArray# size s of { (# s, mbarr# #) ->
- (# s, MallocPtr mbarr# r #)
+ 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 finalizer fptr =
- addForeignPtrConcFinalizer fptr
- (mkFinalizer finalizer (unsafeForeignPtrToPtr fptr))
+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
-- are finalized objects, so a finalizer should not refer to a 'Handle'
-- (including @stdout@, @stdin@ or @stderr@).
--
-addForeignPtrConcFinalizer f@(ForeignPtr fo r) finalizer = do
- fs <- readIORef r
- writeIORef r (finalizer : fs)
- if (null fs)
+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 ->
- let p = unsafeForeignPtrToPtr f in
- case mkWeak# fo () (foreignPtrFinalizer r p) s of
- (# s1, w #) -> (# s1, () #)
+ case r of { IORef (STRef r#) ->
+ case mkWeak# r# () (foreignPtrFinalizer r) s of { (# s1, _ #) ->
+ (# s1, () #) }}
else return ()
-addForeignPtrConcFinalizer f@(MallocPtr fo r) finalizer = do
- fs <- readIORef r
- writeIORef r (finalizer : fs)
- if (null fs)
+addForeignPtrConcFinalizer_ f@(MallocPtr fo r) finalizer = do
+ noFinalizers <- noMixing HaskellFinalizers r (return finalizer)
+ if noFinalizers
then IO $ \s ->
- let p = unsafeForeignPtrToPtr f in
- case mkWeak# fo () (do foreignPtrFinalizer r p
- touchPinnedByteArray# fo) s of
- (# s1, w #) -> (# s1, () #)
+ case mkWeak# fo () (do foreignPtrFinalizer r; touch f) s of
+ (# s1, _ #) -> (# s1, () #)
else return ()
-foreign import ccall "dynamic"
- mkFinalizer :: FinalizerPtr a -> Ptr a -> IO ()
+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 [IO ()] -> Ptr a -> IO ()
-foreignPtrFinalizer r p = do
- fs <- readIORef r
- sequence_ 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 []
- IO $ \ s# ->
- case mkForeignObj# obj s# of
- (# s1#, fo# #) -> (# s1#, ForeignPtr fo# r #)
-
-touchPinnedByteArray# :: MutableByteArray# RealWorld -> IO ()
-touchPinnedByteArray# ba# = IO $ \s -> case touch# ba# s of s -> (# s, () #)
+ r <- newIORef (NoFinalizers, [])
+ return (ForeignPtr obj (PlainForeignPtr r))
touchForeignPtr :: ForeignPtr a -> IO ()
-- ^This function ensures that the foreign object in
-- does a 'touchForeignPtr' after it
-- executes the user action.
--
--- Note that this function should not be used to express liveness
--- dependencies between 'ForeignPtr's. For example, if the finalizer
+-- 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
-- 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.
+-- result in artificial deadlock. Another alternative is to use
+-- explicit reference counting.
--
-touchForeignPtr (ForeignPtr fo r)
- = IO $ \s -> case touch# fo s of s -> (# s, () #)
-touchForeignPtr (MallocPtr fo r)
- = touchPinnedByteArray# fo
+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
-- To avoid subtle coding errors, hand written marshalling code
-- should preferably use 'Foreign.ForeignPtr.withForeignPtr' rather
-- than combinations of 'unsafeForeignPtrToPtr' and
--- 'touchForeignPtr'. However, the later routines
+-- 'touchForeignPtr'. However, the latter routines
-- are occasionally preferred in tool generated marshalling code.
-unsafeForeignPtrToPtr (ForeignPtr fo r) = Ptr (foreignObjToAddr# fo)
-unsafeForeignPtrToPtr (MallocPtr fo r) = Ptr (byteArrayContents# (unsafeCoerce# fo))
+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 a the finalizers associated with a foreign pointer to be run
+-- | Causes the finalizers associated with a foreign pointer to be run
-- immediately.
finalizeForeignPtr :: ForeignPtr a -> IO ()
-finalizeForeignPtr foreignPtr = do
- finalizers <- readIORef refFinalizers
- sequence_ finalizers
- writeIORef refFinalizers []
- where
- refFinalizers = case foreignPtr of
- (ForeignPtr _ ref) -> ref
- (MallocPtr _ ref) -> ref
+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"
+
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