X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FForeignPtr.hs;h=f6a61c1c070cfeb22232cf5fad91bdcc1a9f9e58;hb=e9e2a5412bb7cda8d13a063ac403d9f18ac97380;hp=6b1997038df5b4b9103358e0a71e4a261bd0ab9c;hpb=7196f1ea1790dc0ef7986ae6757bdcf46a286e3f;p=ghc-base.git diff --git a/GHC/ForeignPtr.hs b/GHC/ForeignPtr.hs index 6b19970..f6a61c1 100644 --- a/GHC/ForeignPtr.hs +++ b/GHC/ForeignPtr.hs @@ -1,4 +1,4 @@ -{-# OPTIONS -fno-implicit-prelude #-} +{-# OPTIONS_GHC -fno-implicit-prelude #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.ForeignPtr @@ -17,21 +17,21 @@ module GHC.ForeignPtr ( ForeignPtr(..), FinalizerPtr, - newForeignPtr, + newForeignPtr_, mallocForeignPtr, mallocForeignPtrBytes, addForeignPtrFinalizer, touchForeignPtr, - foreignPtrToPtr, + unsafeForeignPtrToPtr, castForeignPtr, newConcForeignPtr, addForeignPtrConcFinalizer, + finalizeForeignPtr ) where import Control.Monad ( sequence_ ) import Foreign.Ptr import Foreign.Storable -import Data.Dynamic import GHC.List ( null ) import GHC.Base @@ -45,10 +45,10 @@ import GHC.Show -- 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 /finalisers/. A finaliser is a routine that is invoked when +-- 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 finaliser will, then, invoke +-- the 'ForeignPtr'. Typically, the finalizer will, then, invoke -- routines in the foreign language that free the resources bound by -- the foreign object. -- @@ -61,67 +61,48 @@ data ForeignPtr a | MallocPtr (MutableByteArray# RealWorld) !(IORef [IO ()]) instance Eq (ForeignPtr a) where - p == q = foreignPtrToPtr p == foreignPtrToPtr q + p == q = unsafeForeignPtrToPtr p == unsafeForeignPtrToPtr q instance Ord (ForeignPtr a) where - compare p q = compare (foreignPtrToPtr p) (foreignPtrToPtr q) + compare p q = compare (unsafeForeignPtrToPtr p) (unsafeForeignPtrToPtr q) instance Show (ForeignPtr a) where - showsPrec p f = showsPrec p (foreignPtrToPtr f) + showsPrec p f = showsPrec p (unsafeForeignPtrToPtr f) -#include "Dynamic.h" -INSTANCE_TYPEABLE1(ForeignPtr,foreignPtrTc,"ForeignPtr") - --- |A Finaliser 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 ()) -newForeignPtr :: Ptr a -> FinalizerPtr a -> IO (ForeignPtr a) --- ^Turns a plain memory reference into a foreign object by --- associating a finaliser with the reference. The finaliser will be executed --- after the last reference to the foreign object is dropped. Note that there --- is no guarantee on how soon the finaliser is executed after the last --- reference was dropped; this depends on the details of the Haskell storage --- manager. The only guarantee is that the finaliser runs before the program --- terminates. -newForeignPtr p finalizer - = do fObj <- mkForeignPtr p - addForeignPtrFinalizer fObj finalizer - return fObj - newConcForeignPtr :: Ptr a -> IO () -> IO (ForeignPtr a) --- ^Turns a plain memory reference into a foreign object --- by associating a finaliser - given by the monadic operation --- - with the reference. The finaliser will be executed after --- the last reference to the foreign object is dropped. Note --- that there is no guarantee on how soon the finaliser is --- executed after the last reference was dropped; this depends --- on the details of the Haskell storage manager. The only --- guarantee is that the finaliser runs before the program --- terminates. -- --- The finalizer, when invoked, will run in a separate thread. +-- ^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. -- newConcForeignPtr p finalizer - = do fObj <- mkForeignPtr p + = do fObj <- newForeignPtr_ p addForeignPtrConcFinalizer fObj finalizer return fObj mallocForeignPtr :: Storable a => IO (ForeignPtr a) --- ^ allocates some memory and returns a ForeignPtr to it. The memory --- will be released automatically when the ForeignPtr is discarded. +-- ^ Allocate some memory and return a 'ForeignPtr' to it. The memory +-- will be released automatically when the 'ForeignPtr' is discarded. -- --- @mallocForeignPtr@ is equivalent to +-- 'mallocForeignPtr' is equivalent to -- --- > do { p <- malloc; newForeignPtr p free } +-- > do { p <- malloc; newForeignPtr finalizerFree p } -- --- although it may be implemented differently internally. You may not +-- although it may be implemented differently internally: you may not -- assume that the memory returned by 'mallocForeignPtr' has been --- allocated with C's @malloc()@. +-- allocated with 'Foreign.Marshal.Alloc.malloc'. mallocForeignPtr = doMalloc undefined - where doMalloc :: Storable a => a -> IO (ForeignPtr a) + where doMalloc :: Storable b => b -> IO (ForeignPtr b) doMalloc a = do r <- newIORef [] IO $ \s -> @@ -130,8 +111,8 @@ mallocForeignPtr = doMalloc undefined } where (I# size) = sizeOf a --- | similar to 'mallocForeignPtr', except that the size of the memory required --- is given explicitly as a number of bytes. +-- | 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 (I# size) = do r <- newIORef [] @@ -140,16 +121,16 @@ mallocForeignPtrBytes (I# size) = do (# s, MallocPtr mbarr# r #) } -addForeignPtrFinalizer :: ForeignPtr a -> FinalizerPtr a -> IO () --- ^This function adds a finaliser to the given foreign object. The +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 fptr finalizer = +addForeignPtrFinalizer finalizer fptr = addForeignPtrConcFinalizer fptr - (mkFinalizer finalizer (foreignPtrToPtr fptr)) + (mkFinalizer finalizer (unsafeForeignPtrToPtr fptr)) addForeignPtrConcFinalizer :: ForeignPtr a -> IO () -> IO () --- ^This function adds a finaliser to the given @ForeignPtr@. The +-- ^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. -- @@ -157,12 +138,18 @@ addForeignPtrConcFinalizer :: ForeignPtr a -> IO () -> IO () -- 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 f@(ForeignPtr fo r) finalizer = do fs <- readIORef r writeIORef r (finalizer : fs) if (null fs) then IO $ \s -> - let p = foreignPtrToPtr f in + let p = unsafeForeignPtrToPtr f in case mkWeak# fo () (foreignPtrFinalizer r p) s of (# s1, w #) -> (# s1, () #) else return () @@ -171,8 +158,9 @@ addForeignPtrConcFinalizer f@(MallocPtr fo r) finalizer = do writeIORef r (finalizer : fs) if (null fs) then IO $ \s -> - let p = foreignPtrToPtr f in - case mkWeak# fo () (foreignPtrFinalizer r p) s of + let p = unsafeForeignPtrToPtr f in + case mkWeak# fo () (do foreignPtrFinalizer r p + touchPinnedByteArray# fo) s of (# s1, w #) -> (# s1, () #) else return () @@ -184,56 +172,78 @@ foreignPtrFinalizer r p = do fs <- readIORef r sequence_ fs -mkForeignPtr :: Ptr a -> IO (ForeignPtr a) {- not exported -} -mkForeignPtr (Ptr obj) = do +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, () #) + 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 'withForeignPtr' +-- actions. In particular 'Foreign.ForeignPtr.withForeignPtr' -- does a 'touchForeignPtr' after it -- executes the user action. -- --- This function can be used to express liveness --- dependencies between 'ForeignPtr's: for --- example, if the finalizer for one --- 'ForeignPtr' touches a second --- 'ForeignPtr', then it is ensured that the --- second 'ForeignPtr' will stay alive at --- least as long as the first. This can be useful when you --- want to manipulate /interior pointers/ to --- a foreign structure: you can use --- 'touchForeignObj' to express the --- requirement that the exterior pointer must not be finalized --- until the interior pointer is no longer referenced. +-- Note that this function should not be used to express liveness +-- dependencies between '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. +-- touchForeignPtr (ForeignPtr fo r) = IO $ \s -> case touch# fo s of s -> (# s, () #) touchForeignPtr (MallocPtr fo r) - = IO $ \s -> case touch# fo s of s -> (# s, () #) + = touchPinnedByteArray# fo -foreignPtrToPtr :: ForeignPtr a -> Ptr a +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 'foreignPtrToPtr' is the last usage --- occurence of the given foreign pointer, then its finaliser(s) will +-- 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 'withForeignPtr' rather --- than combinations of 'foreignPtrToPtr' and +-- should preferably use 'Foreign.ForeignPtr.withForeignPtr' rather +-- than combinations of 'unsafeForeignPtrToPtr' and -- 'touchForeignPtr'. However, the later routines -- are occasionally preferred in tool generated marshalling code. -foreignPtrToPtr (ForeignPtr fo r) = Ptr (foreignObjToAddr# fo) -foreignPtrToPtr (MallocPtr fo r) = Ptr (byteArrayContents# (unsafeCoerce# fo)) +unsafeForeignPtrToPtr (ForeignPtr fo r) = Ptr (foreignObjToAddr# fo) +unsafeForeignPtrToPtr (MallocPtr fo r) = Ptr (byteArrayContents# (unsafeCoerce# 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 +-- 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