X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FForeignPtr.hs;h=971276379a3664723d4c60b197f130f198b08129;hb=85c40b892e70030f8e41ba56dd7ac735d91fe1fa;hp=430d3ad5b5c66960c61e3966d36ad75408000ac1;hpb=acd78d6dbda0108ffa899cb585114a21c5ed7499;p=haskell-directory.git diff --git a/GHC/ForeignPtr.hs b/GHC/ForeignPtr.hs index 430d3ad..9712763 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 @@ -13,6 +13,7 @@ -- ----------------------------------------------------------------------------- +-- #hide module GHC.ForeignPtr ( ForeignPtr(..), @@ -26,16 +27,17 @@ module GHC.ForeignPtr 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 import GHC.IOBase +import GHC.STRef ( STRef(..) ) import GHC.Ptr ( Ptr(..) ) import GHC.Err import GHC.Show @@ -45,10 +47,10 @@ 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. -- @@ -56,8 +58,19 @@ import GHC.Show -- type argument of 'ForeignPtr' should normally be an instance of -- class 'Storable'. -- -data ForeignPtr a - = ForeignPtr ForeignObj# !(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 + = PlainForeignPtr !(IORef [IO ()]) | MallocPtr (MutableByteArray# RealWorld) !(IORef [IO ()]) instance Eq (ForeignPtr a) where @@ -69,27 +82,28 @@ instance Ord (ForeignPtr a) where instance Show (ForeignPtr a) where showsPrec p f = showsPrec p (unsafeForeignPtrToPtr f) -#include "Typeable.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 ()) 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. +-- +-- 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 @@ -97,46 +111,48 @@ newConcForeignPtr p 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 -> case newPinnedByteArray# size s of { (# s, mbarr# #) -> - (# s, MallocPtr mbarr# r #) + (# s, ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#)) + (MallocPtr mbarr# r) #) } 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 [] IO $ \s -> case newPinnedByteArray# size s of { (# s, mbarr# #) -> - (# s, MallocPtr mbarr# r #) + (# s, ForeignPtr (byteArrayContents# (unsafeCoerce# mbarr#)) + (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 (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. -- @@ -144,85 +160,105 @@ addForeignPtrConcFinalizer :: ForeignPtr a -> IO () -> IO () -- is an arbitrary @IO@ action. When it is invoked, the finalizer -- will run in a new thread. -- -addForeignPtrConcFinalizer f@(ForeignPtr fo r) finalizer = do +-- 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 a c) finalizer = + addForeignPtrConcFinalizer_ c finalizer + +addForeignPtrConcFinalizer_ f@(PlainForeignPtr 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, () #) + case r of { IORef (STRef r#) -> + case mkWeak# r# () (foreignPtrFinalizer r) s of { (# s1, w #) -> + (# s1, () #) }} else return () -addForeignPtrConcFinalizer f@(MallocPtr fo r) finalizer = do +addForeignPtrConcFinalizer_ f@(MallocPtr 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 () (foreignPtrFinalizer r p) s of + case mkWeak# fo () (do foreignPtrFinalizer r; touch f) 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 #) + 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 '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. -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, () #) +-- 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 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 -- pointer. This is a potentially dangerous operations, as if the -- argument to 'unsafeForeignPtrToPtr' is the last usage --- occurence of the given foreign pointer, then its finaliser(s) will +-- 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 +-- 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. -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' -- 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 _ foreignPtr) = do + finalizers <- readIORef refFinalizers + sequence_ finalizers + writeIORef refFinalizers [] + where + refFinalizers = case foreignPtr of + (PlainForeignPtr ref) -> ref + (MallocPtr _ ref) -> ref