ForeignPtr

module Foreign.ForeignPtr
base Foreign.ForeignPtr
The ForeignPtr type and operations. This module is part of the Foreign Function Interface (FFI) and will usually be imported via the Foreign module.
data ForeignPtr a
base Foreign.ForeignPtr
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.
addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO ()
base Foreign.ForeignPtr
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 :: ForeignPtr a -> IO () -> IO ()
base Foreign.Concurrent
This function adds a finalizer to the given ForeignPtr. The finalizer will run after the last reference to the foreign object is dropped, but before all previously registered finalizers for the same object.
addForeignPtrFinalizerEnv :: FinalizerEnvPtr env a -> Ptr env -> ForeignPtr a -> IO ()
base Foreign.ForeignPtr
Like addForeignPtrFinalizerEnv but allows the finalizer to be passed an additional environment parameter to be passed to the finalizer. The environment passed to the finalizer is fixed by the second argument to addForeignPtrFinalizerEnv
castForeignPtr :: ForeignPtr a -> ForeignPtr b
base Foreign.ForeignPtr
This function casts a ForeignPtr parameterised by one type into another type.
finalizeForeignPtr :: ForeignPtr a -> IO ()
base Foreign.ForeignPtr
Causes the finalizers associated with a foreign pointer to be run immediately.
mallocForeignPtr :: Storable a => IO (ForeignPtr a)
base Foreign.ForeignPtr
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 Foreign.Marshal.Alloc.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.
mallocForeignPtrArray :: Storable a => Int -> IO (ForeignPtr a)
base Foreign.ForeignPtr
This function is similar to Foreign.Marshal.Array.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 Foreign.Marshal.Alloc.malloc.
mallocForeignPtrArray0 :: Storable a => Int -> IO (ForeignPtr a)
base Foreign.ForeignPtr
This function is similar to Foreign.Marshal.Array.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 Foreign.Marshal.Alloc.malloc.
mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
base Foreign.ForeignPtr
This function is similar to mallocForeignPtr, except that the size of the memory required is given explicitly as a number of bytes.
newForeignPtr :: FinalizerPtr a -> Ptr a -> IO (ForeignPtr a)
base Foreign.ForeignPtr
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 () -> IO (ForeignPtr a)
base Foreign.Concurrent
Turns a plain memory reference into a foreign object by associating a finalizer - given by the monadic operation - with the reference. The finalizer will be executed after the last reference to the foreign object is dropped. There is no guarantee of promptness, and in fact there is no guarantee that the finalizer will eventually run at all.
newForeignPtr_ :: Ptr a -> IO (ForeignPtr a)
base Foreign.ForeignPtr
Turns a plain memory reference into a foreign pointer that may be associated with finalizers by using addForeignPtrFinalizer.
newForeignPtrEnv :: FinalizerEnvPtr env a -> Ptr env -> Ptr a -> IO (ForeignPtr a)
base Foreign.ForeignPtr
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.
touchForeignPtr :: ForeignPtr a -> IO ()
base Foreign.ForeignPtr
This function ensures that the foreign object in question is alive at the given place in the sequence of IO actions. In particular Foreign.ForeignPtr.withForeignPtr does a touchForeignPtr after it executes the user action. 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.
unsafeForeignPtrToPtr :: ForeignPtr a -> Ptr a
base Foreign.ForeignPtr
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 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 Foreign.ForeignPtr.withForeignPtr rather than combinations of unsafeForeignPtrToPtr and touchForeignPtr. However, the latter routines are occasionally preferred in tool generated marshalling code.
withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b
base Foreign.ForeignPtr
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.
package aligned-foreignptr
package
An aligned ForeignPtr type. Version 0.1
asForeignPtr :: Text -> IO (ForeignPtr Word16, I16)
text Data.Text.Foreign
O(n) Make a mutable copy of a Text.
unsafeForeignPtrToStorableArray :: Ix i => ForeignPtr e -> (i, i) -> IO (StorableArray i e)
array Data.Array.Unsafe, array Data.Array.Storable
Construct a StorableArray from an arbitrary ForeignPtr. It is the caller's responsibility to ensure that the ForeignPtr points to an area of memory sufficient for the specified bounds.