import Foreign.Ptr
import Foreign.Storable
-import GHC.List ( null )
import GHC.Base
import GHC.IOBase
+import GHC.STRef ( STRef(..) )
import GHC.Ptr ( Ptr(..) )
import GHC.Err
import GHC.Show
-- 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.
+
+data ForeignPtrContents
+ = PlainNoFinalizer
+ | PlainWithFinalizer !(IORef [IO ()])
+ | MallocPtrNoFinalizer (MutableByteArray# RealWorld)
+ | MallocPtrWithFinalizer (MutableByteArray# RealWorld) !(IORef [IO ()])
+ -- we optimise the no-finalizer case, which is especially common
+ -- with a MallocPtr. mallocForeignPtr doesn't have to create an
+ -- IORef, or set up a weak pointer.
instance Eq (ForeignPtr a) where
p == q = unsafeForeignPtrToPtr p == unsafeForeignPtrToPtr q
-- 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
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 #)
+ (# s, ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
+ (MallocPtrNoFinalizer mbarr#) #)
}
where (I# size) = sizeOf a
-- size of the memory required is given explicitly as a number of bytes.
mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
mallocForeignPtrBytes (I# size) = do
- r <- newIORef []
IO $ \s ->
case newPinnedByteArray# size s of { (# s, mbarr# #) ->
- (# s, MallocPtr mbarr# r #)
+ (# s, ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#))
+ (MallocPtrNoFinalizer mbarr#) #)
}
addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO ()
-- are finalized objects, so a finalizer should not refer to a 'Handle'
-- (including @stdout@, @stdin@ or @stderr@).
--
-addForeignPtrConcFinalizer f@(ForeignPtr fo r) finalizer = do
+addForeignPtrConcFinalizer (ForeignPtr a c) finalizer =
+ addForeignPtrConcFinalizer_ c finalizer
+
+addForeignPtrConcFinalizer_ PlainNoFinalizer finalizer = do
+ r <- newIORef []
+ IO $ \s -> case r of { IORef (STRef r#) ->
+ case mkWeak# r# () (foreignPtrFinalizer r) s of { (# s1, w #) ->
+ (# s1, () #) }}
+ addForeignPtrConcFinalizer_ (PlainWithFinalizer r) finalizer
+
+addForeignPtrConcFinalizer_ f@(PlainWithFinalizer r) finalizer = do
fs <- readIORef r
writeIORef r (finalizer : fs)
- if (null fs)
- then IO $ \s ->
- let p = unsafeForeignPtrToPtr f in
- case mkWeak# fo () (foreignPtrFinalizer r p) s of
- (# s1, w #) -> (# s1, () #)
- else return ()
-addForeignPtrConcFinalizer f@(MallocPtr fo r) finalizer = do
+
+addForeignPtrConcFinalizer_ f@(MallocPtrNoFinalizer fo) finalizer = do
+ r <- newIORef []
+ IO $ \s -> case mkWeak# fo () (do foreignPtrFinalizer r; touch f) s of
+ (# s1, w #) -> (# s1, () #)
+ addForeignPtrConcFinalizer_ (MallocPtrWithFinalizer fo r) finalizer
+
+addForeignPtrConcFinalizer_ f@(MallocPtrWithFinalizer fo r) finalizer = do
fs <- readIORef r
writeIORef r (finalizer : fs)
- if (null fs)
- then IO $ \s ->
- let p = unsafeForeignPtrToPtr f in
- case mkWeak# fo () (do foreignPtrFinalizer r p
- touchPinnedByteArray# fo) s of
- (# s1, w #) -> (# s1, () #)
- else return ()
foreign import ccall "dynamic"
mkFinalizer :: FinalizerPtr a -> Ptr a -> IO ()
-foreignPtrFinalizer :: IORef [IO ()] -> Ptr a -> IO ()
-foreignPtrFinalizer r p = do
- fs <- readIORef r
- sequence_ fs
+foreignPtrFinalizer :: IORef [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, () #)
+newForeignPtr_ (Ptr obj) = return (ForeignPtr obj PlainNoFinalizer)
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 fo r) = touch r
+
+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
-- than combinations of 'unsafeForeignPtrToPtr' and
-- 'touchForeignPtr'. However, the later 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 r) = Ptr fo
castForeignPtr :: ForeignPtr a -> ForeignPtr b
-- ^This function casts a 'ForeignPtr'
-- | 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 _ contents) = do
+ case contents of
+ PlainNoFinalizer -> return ()
+ PlainWithFinalizer r -> runFinalizers r
+ MallocPtrNoFinalizer _ -> return ()
+ MallocPtrWithFinalizer _ r -> runFinalizers r
+ where
+ runFinalizers r = do
+ fs <- readIORef r
+ sequence_ fs
+ writeIORef r []
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