FinalizerPtr,
newForeignPtr_,
mallocForeignPtr,
+ mallocPlainForeignPtr,
mallocForeignPtrBytes,
+ mallocPlainForeignPtrBytes,
addForeignPtrFinalizer,
touchForeignPtr,
unsafeForeignPtrToPtr,
) where
import Control.Monad ( sequence_ )
-import Foreign.Ptr
import Foreign.Storable
+import GHC.Show
import GHC.List ( null )
import GHC.Base
import GHC.IOBase
import GHC.STRef ( STRef(..) )
-import GHC.Ptr ( Ptr(..) )
+import GHC.Ptr ( Ptr(..), FunPtr )
import GHC.Err
-import GHC.Show
-- |The type 'ForeignPtr' represents references to objects that are
-- maintained in a foreign language, i.e., that are not part of the
-- object, because that ensures that whatever the finalizer is
-- attached to is kept alive.
-data ForeignPtrContents
+data ForeignPtrContents
= PlainForeignPtr !(IORef [IO ()])
- | MallocPtr (MutableByteArray# RealWorld) !(IORef [IO ()])
+ | MallocPtr (MutableByteArray# RealWorld) !(IORef [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
-- finalisation time, gets as an argument a plain pointer variant of the
-- foreign pointer that the finalizer is associated with.
-- 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
(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 = IO $ \s ->
+ case newPinnedByteArray# size s of { (# s, mbarr# #) ->
+ (# s, ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
+ (PlainPtr mbarr#) #)
+ }
+ where (I# size) = sizeOf 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 (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
(# s1, w #) -> (# s1, () #)
else return ()
+addForeignPtrConcFinalizer_ _ _ =
+ error "GHC.ForeignPtr: attempt to add a finalizer to plain pointer"
+
foreign import ccall "dynamic"
mkFinalizer :: FinalizerPtr a -> Ptr a -> IO ()
-- 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) = touch r
-- | 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
finalizers <- readIORef refFinalizers
sequence_ finalizers
where
refFinalizers = case foreignPtr of
(PlainForeignPtr ref) -> ref
- (MallocPtr _ ref) -> ref
+ (MallocPtr _ ref) -> ref
+
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