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 |
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 Source #
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 ForeignPtr
s 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
Eq (ForeignPtr a) Source # | Since: 2.1 |
Defined in GHC.ForeignPtr (==) :: ForeignPtr a -> ForeignPtr a -> Bool # (/=) :: ForeignPtr a -> ForeignPtr a -> Bool # | |
Data a => Data (ForeignPtr a) Source # | Since: 4.8.0.0 |
Defined in Data.Data gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ForeignPtr a -> c (ForeignPtr a) Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ForeignPtr a) Source # toConstr :: ForeignPtr a -> Constr Source # dataTypeOf :: ForeignPtr a -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (ForeignPtr a)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ForeignPtr a)) Source # gmapT :: (forall b. Data b => b -> b) -> ForeignPtr a -> ForeignPtr a Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ForeignPtr a -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ForeignPtr a -> r Source # gmapQ :: (forall d. Data d => d -> u) -> ForeignPtr a -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> ForeignPtr a -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ForeignPtr a -> m (ForeignPtr a) Source # | |
Ord (ForeignPtr a) Source # | Since: 2.1 |
Defined in GHC.ForeignPtr compare :: ForeignPtr a -> ForeignPtr a -> Ordering # (<) :: ForeignPtr a -> ForeignPtr a -> Bool # (<=) :: ForeignPtr a -> ForeignPtr a -> Bool # (>) :: ForeignPtr a -> ForeignPtr a -> Bool # (>=) :: ForeignPtr a -> ForeignPtr a -> Bool # max :: ForeignPtr a -> ForeignPtr a -> ForeignPtr a # min :: ForeignPtr a -> ForeignPtr a -> ForeignPtr a # | |
Show (ForeignPtr a) Source # | Since: 2.1 |
Defined in GHC.ForeignPtr |
type FinalizerPtr a = FunPtr (Ptr a -> IO ()) Source #
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) Source #
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) Source #
Turns a plain memory reference into a foreign pointer that may be
associated with finalizers by using addForeignPtrFinalizer
.
addForeignPtrFinalizer :: FinalizerPtr a -> ForeignPtr a -> IO () Source #
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) Source #
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 () Source #
Like addForeignPtrFinalizer
but the finalizer is passed an additional
environment parameter.
withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b Source #
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 () Source #
Causes the finalizers associated with a foreign pointer to be run immediately.
Low-level operations
touchForeignPtr :: ForeignPtr a -> IO () Source #
This function ensures that the foreign object in
question is alive at the given place in the sequence of IO
actions. In particular withForeignPtr
does a touchForeignPtr
after it
executes the user action.
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.
castForeignPtr :: ForeignPtr a -> ForeignPtr b Source #
This function casts a ForeignPtr
parameterised by one type into another type.
plusForeignPtr :: ForeignPtr a -> Int -> ForeignPtr b Source #
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: 4.10.0.0
Allocating managed memory
mallocForeignPtr :: Storable a => IO (ForeignPtr a) Source #
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) Source #
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) Source #
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) Source #
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
.