X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FForeignPtr.hs;h=ee95828cabe759f974fd3d11b60265f40176e12d;hb=c5739b9a47edd8003719fdc8c43b43947f95102f;hp=216f5789a1d49df890be1567637028ddc9cdf738;hpb=f444698bf6b09b2da6a1fec8aecc1eaf37847980;p=ghc-base.git diff --git a/GHC/ForeignPtr.hs b/GHC/ForeignPtr.hs index 216f578..ee95828 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(..), @@ -26,12 +27,12 @@ module GHC.ForeignPtr castForeignPtr, newConcForeignPtr, addForeignPtrConcFinalizer, + finalizeForeignPtr ) where import Control.Monad ( sequence_ ) import Foreign.Ptr import Foreign.Storable -import Data.Typeable import GHC.List ( null ) import GHC.Base @@ -45,10 +46,10 @@ 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. -- @@ -69,27 +70,21 @@ 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. -- newConcForeignPtr p finalizer = do fObj <- newForeignPtr_ p @@ -108,7 +103,7 @@ mallocForeignPtr :: Storable a => IO (ForeignPtr a) -- assume that the memory returned by 'mallocForeignPtr' has been -- 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 -> @@ -128,7 +123,7 @@ mallocForeignPtrBytes (I# size) = do } addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO () --- ^This function adds a finaliser to the given foreign object. The +-- ^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 = @@ -136,7 +131,7 @@ addForeignPtrFinalizer finalizer 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. -- @@ -144,6 +139,12 @@ 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) @@ -191,18 +192,23 @@ touchForeignPtr :: ForeignPtr a -> IO () -- 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) @@ -212,7 +218,7 @@ 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., @@ -230,3 +236,15 @@ 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 = do + finalizers <- readIORef refFinalizers + sequence_ finalizers + writeIORef refFinalizers [] + where + refFinalizers = case foreignPtr of + (ForeignPtr _ ref) -> ref + (MallocPtr _ ref) -> ref