| Copyright | (c) The University of Glasgow 2001 | 
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) | 
| Maintainer | ffi@haskell.org | 
| Stability | provisional | 
| Portability | portable | 
| Safe Haskell | Trustworthy | 
| Language | Haskell2010 | 
Foreign.ForeignPtr
Description
The ForeignPtr type and operations.  This module is part of the
 Foreign Function Interface (FFI) and will usually be imported via
 the Foreign module.
For non-portable support of Haskell finalizers, see the Foreign.Concurrent module.
Synopsis
- data ForeignPtr a
- type FinalizerPtr a = FunPtr (Ptr a -> IO ())
- type FinalizerEnvPtr env a = FunPtr (Ptr env -> Ptr a -> IO ())
- newForeignPtr :: FinalizerPtr a -> Ptr a -> IO (ForeignPtr a)
- newForeignPtr_ :: Ptr a -> IO (ForeignPtr a)
- addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO ()
- newForeignPtrEnv :: FinalizerEnvPtr env a -> Ptr env -> Ptr a -> IO (ForeignPtr a)
- addForeignPtrFinalizerEnv :: FinalizerEnvPtr env a -> Ptr env -> ForeignPtr a -> IO ()
- withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b
- finalizeForeignPtr :: ForeignPtr a -> IO ()
- touchForeignPtr :: ForeignPtr a -> IO ()
- castForeignPtr :: ForeignPtr a -> ForeignPtr b
- plusForeignPtr :: ForeignPtr a -> Int -> ForeignPtr b
- mallocForeignPtr :: Storable a => IO (ForeignPtr a)
- mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
- mallocForeignPtrArray :: Storable a => Int -> IO (ForeignPtr a)
- mallocForeignPtrArray0 :: Storable a => Int -> IO (ForeignPtr a)
Finalised data pointers
data ForeignPtr a #
The type ForeignPtr represents references to objects that are
 maintained in a foreign language, i.e., that are not part of the
 data structures usually managed by the Haskell storage manager.
 The essential difference between ForeignPtrs and vanilla memory
 references of type Ptr a is that the former may be associated
 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 finalizer will, then, invoke
 routines in the foreign language that free the resources bound by
 the foreign object.
The ForeignPtr is parameterised in the same way as Ptr.  The
 type argument of ForeignPtr should normally be an instance of
 class Storable.
Instances
| Data a => Data (ForeignPtr a) # | Since: base-4.8.0.0 | 
| Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ForeignPtr a -> c (ForeignPtr a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ForeignPtr a) # toConstr :: ForeignPtr a -> Constr # dataTypeOf :: ForeignPtr a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (ForeignPtr a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ForeignPtr a)) # gmapT :: (forall b. Data b => b -> b) -> ForeignPtr a -> ForeignPtr a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ForeignPtr a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ForeignPtr a -> r # gmapQ :: (forall d. Data d => d -> u) -> ForeignPtr a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> ForeignPtr a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) # | |
| Show (ForeignPtr a) # | Since: base-2.1 | 
| Defined in GHC.ForeignPtr Methods showsPrec :: Int -> ForeignPtr a -> ShowS # show :: ForeignPtr a -> String # showList :: [ForeignPtr a] -> ShowS # | |
| Eq (ForeignPtr a) # | Since: base-2.1 | 
| Defined in GHC.ForeignPtr Methods (==) :: ForeignPtr a -> ForeignPtr a -> Bool Source # (/=) :: ForeignPtr a -> ForeignPtr a -> Bool Source # | |
| Ord (ForeignPtr a) # | Since: base-2.1 | 
| Defined in GHC.ForeignPtr Methods compare :: ForeignPtr a -> ForeignPtr a -> Ordering Source # (<) :: ForeignPtr a -> ForeignPtr a -> Bool Source # (<=) :: ForeignPtr a -> ForeignPtr a -> Bool Source # (>) :: ForeignPtr a -> ForeignPtr a -> Bool Source # (>=) :: ForeignPtr a -> ForeignPtr a -> Bool Source # max :: ForeignPtr a -> ForeignPtr a -> ForeignPtr a Source # min :: ForeignPtr a -> ForeignPtr a -> ForeignPtr a Source # | |
type FinalizerPtr a = FunPtr (Ptr a -> IO ()) #
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.
Note that the foreign function must use the ccall calling convention.
Basic operations
newForeignPtr :: FinalizerPtr a -> Ptr a -> IO (ForeignPtr a) #
Turns a plain memory reference into a foreign pointer, and associates a finalizer with the reference. The finalizer will be executed after the last reference to the foreign object is dropped. There is no guarantee of promptness, however the finalizer will be executed before the program exits.
newForeignPtr_ :: Ptr a -> IO (ForeignPtr a) #
Turns a plain memory reference into a foreign pointer that may be
 associated with finalizers by using addForeignPtrFinalizer.
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.
newForeignPtrEnv :: FinalizerEnvPtr env a -> Ptr env -> Ptr a -> IO (ForeignPtr a) #
This variant of newForeignPtr adds a finalizer that expects an
 environment in addition to the finalized pointer.  The environment
 that will be passed to the finalizer is fixed by the second argument to
 newForeignPtrEnv.
addForeignPtrFinalizerEnv :: FinalizerEnvPtr env a -> Ptr env -> ForeignPtr a -> IO () #
Like addForeignPtrFinalizer but the finalizer is passed an additional
 environment parameter.
withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b #
This is a way to look at the pointer living inside a
 foreign object.  This function takes a function which is
 applied to that pointer. The resulting IO action is then
 executed. The foreign object is kept alive at least during
 the whole action, even if it is not used directly
 inside. Note that it is not safe to return the pointer from
 the action and use it after the action completes. All uses
 of the pointer should be inside the
 withForeignPtr bracket.  The reason for
 this unsafeness is the same as for
 unsafeForeignPtrToPtr below: the finalizer
 may run earlier than expected, because the compiler can only
 track usage of the ForeignPtr object, not
 a Ptr object made from it.
This function is normally used for marshalling data to
 or from the object pointed to by the
 ForeignPtr, using the operations from the
 Storable class.
finalizeForeignPtr :: ForeignPtr a -> IO () #
Causes the finalizers associated with a foreign pointer to be run immediately. The foreign pointer must not be used again after this function is called. If the foreign pointer does not support finalizers, this is a no-op.
Low-level operations
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. However, this comes with a significant caveat: the contract above
 does not hold if GHC can demonstrate that the code preceeding
 touchForeignPtr diverges (e.g. by looping infinitely or throwing an
 exception). For this reason, you are strongly advised to use instead
 withForeignPtr where possible.
Also, note that this function should not be used to express dependencies
 between finalizers on ForeignPtrs.  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 MVars
 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.
castForeignPtr :: ForeignPtr a -> ForeignPtr b #
This function casts a ForeignPtr
 parameterised by one type into another type.
plusForeignPtr :: ForeignPtr a -> Int -> ForeignPtr b #
Advances the given address by the given offset in bytes.
The new ForeignPtr shares the finalizer of the original,
 equivalent from a finalization standpoint to just creating another
 reference to the original. That is, the finalizer will not be
 called before the new ForeignPtr is unreachable, nor will it be
 called an additional time due to this call, and the finalizer will
 be called with the same address that it would have had this call
 not happened, *not* the new address.
Since: base-4.10.0.0
Allocating managed memory
mallocForeignPtr :: Storable a => IO (ForeignPtr a) #
Allocate some memory and return a ForeignPtr to it.  The memory
 will be released automatically when the ForeignPtr is discarded.
mallocForeignPtr is equivalent to
   do { p <- malloc; newForeignPtr finalizerFree p }although it may be implemented differently internally: you may not
 assume that the memory returned by mallocForeignPtr has been
 allocated with 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.
mallocForeignPtrBytes :: Int -> IO (ForeignPtr a) #
This function is similar to mallocForeignPtr, except that the
 size of the memory required is given explicitly as a number of bytes.
mallocForeignPtrArray :: Storable a => Int -> IO (ForeignPtr a) #
This function is similar to mallocArray,
 but yields a memory area that has a finalizer attached that releases
 the memory area.  As with mallocForeignPtr, it is not guaranteed that
 the block of memory was allocated by malloc.
mallocForeignPtrArray0 :: Storable a => Int -> IO (ForeignPtr a) #
This function is similar to mallocArray0,
 but yields a memory area that has a finalizer attached that releases
 the memory area.  As with mallocForeignPtr, it is not guaranteed that
 the block of memory was allocated by malloc.