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| GHC.Stable | | Portability | non-portable (GHC Extensions) | | Stability | internal | | Maintainer | ffi@haskell.org |
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| Description |
| Stable pointers.
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| Synopsis |
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| Documentation |
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| 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 | | | Instances | |
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| newStablePtr :: a -> IO (StablePtr a) |
| Create a stable pointer referring to the given Haskell value.
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| 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.
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| 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.
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| 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.
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| 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.
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| Produced by Haddock version 0.6 |
