| Haskell Hierarchical Libraries (base package) | Contents | Index

GHC.Stable

Portability | non-portable (GHC Extensions)
Stability | internal
Maintainer | ffi@haskell.org

Description
Stable pointers.
Synopsis

data StablePtr a = StablePtr (StablePtr# a)
newStablePtr :: a -> IO (StablePtr a)
deRefStablePtr :: StablePtr a -> IO a
freeStablePtr :: StablePtr a -> IO ()
castStablePtrToPtr :: StablePtr a -> Ptr ()
castPtrToStablePtr :: Ptr () -> StablePtr a

Documentation
data StablePtr a

A stable pointer is a reference to a Haskell expression that is guaranteed not to be affected by garbage collection, i.e., it will neither be deallocated nor will the value of the stable pointer itself change during garbage collection (ordinary references may be relocated during garbage collection). Consequently, stable pointers can be passed to foreign code, which can treat it as an opaque reference to a Haskell value.

A value of type `StablePtr a` is a stable pointer to a Haskell expression of type `a`.

Constructors

StablePtr (StablePtr# a) |

Instances

IArray UArray (StablePtr a)
Ix ix => Eq (UArray ix (StablePtr a))
MArray (STUArray s) (StablePtr a) (ST s)
IArray (IOToDiffArray IOUArray) (StablePtr a)
MArray IOUArray (StablePtr a) IO
Typeable a => Typeable (StablePtr a)
Storable (StablePtr a)
Eq (StablePtr a)

newStablePtr :: a -> IO (StablePtr a)
Create a stable pointer referring to the given Haskell value.
deRefStablePtr :: StablePtr a -> IO a
Obtain the Haskell value referenced by a stable pointer, i.e., the same value that was passed to the corresponding call to makeStablePtr. If the argument to `deRefStablePtr` has already been freed using `freeStablePtr`, the behaviour of `deRefStablePtr` is undefined.
freeStablePtr :: StablePtr a -> IO ()

Dissolve the association between the stable pointer and the Haskell value. Afterwards, if the stable pointer is passed to `deRefStablePtr` or `freeStablePtr`, the behaviour is undefined. However, the stable pointer may still be passed to `castStablePtrToPtr`, but the `Ptr ()` value returned by `castStablePtrToPtr`, in this case, is undefined (in particular, it may be `nullPtr`). Nevertheless, the call to `castStablePtrToPtr` is guaranteed not to diverge.

castStablePtrToPtr :: StablePtr a -> Ptr ()
Coerce a stable pointer to an address. No guarantees are made about the resulting value, except that the original stable pointer can be recovered by `castPtrToStablePtr`. In particular, the address may not refer to an accessible memory location and any attempt to pass it to the member functions of the class `Storable` leads to undefined behaviour.
castPtrToStablePtr :: Ptr () -> StablePtr a

The inverse of `castStablePtrToPtr`, i.e., we have the identity

     sp == castPtrToStablePtr (castStablePtrToPtr sp)

for any stable pointer `sp` on which `freeStablePtr` has not been executed yet. Moreover, `castPtrToStablePtr` may only be applied to pointers that have been produced by `castStablePtrToPtr`.

Produced by Haddock version 0.6