GHC.StaticPtr

Symbolic references to values.

References to values are usually implemented with memory addresses, and this is practical when communicating values between the different pieces of a single process.

When values are communicated across different processes running in possibly different machines, though, addresses are no longer useful since each process may use different addresses to store a given value.

To solve such concern, the references provided by this module offer a key that can be used to locate the values on each process. Each process maintains a global table of references which can be looked up with a given key. This table is known as the Static Pointer Table. The reference can then be dereferenced to obtain the value.

The various communicating processes need to agree on the keys used to refer to the values in the Static Pointer Table, or lookups will fail. Only processes launched from the same program binary are guaranteed to use the same set of keys.

Documentation

data StaticPtr a

A reference to a value of type a.

Instances

IsStatic StaticPtr

Since: base-4.9.0.0

Defined in GHC.Internal.StaticPtr

Methods

fromStaticPtr :: Typeable a => StaticPtr a -> StaticPtr a

deRefStaticPtr :: StaticPtr a -> a

Dereferences a static pointer.

type StaticKey = Fingerprint

A key for StaticPtrs that can be serialized and used with unsafeLookupStaticPtr.

staticKey :: StaticPtr a -> StaticKey

The StaticKey that can be used to look up the given StaticPtr.

unsafeLookupStaticPtr :: StaticKey -> IO (Maybe (StaticPtr a))

Looks up a StaticPtr by its StaticKey.

If the StaticPtr is not found returns Nothing.

This function is unsafe because the program behavior is undefined if the type of the returned StaticPtr does not match the expected one.

data StaticPtrInfo

Miscellaneous information available for debugging purposes.

Constructors

StaticPtrInfo

Fields

• spInfoUnitId :: String

  Package key of the package where the static pointer is defined

• spInfoModuleName :: String

  Name of the module where the static pointer is defined

• spInfoSrcLoc :: (Int, Int)

  Source location of the definition of the static pointer as a (Line, Column) pair.

Instances

Show StaticPtrInfo

Since: base-4.8.0.0

Defined in GHC.Internal.StaticPtr

Methods

showsPrec :: Int -> StaticPtrInfo -> ShowS

show :: StaticPtrInfo -> String

showList :: [StaticPtrInfo] -> ShowS

staticPtrInfo :: StaticPtr a -> StaticPtrInfo

StaticPtrInfo of the given StaticPtr.

staticPtrKeys :: IO [StaticKey]

A list of all known keys.

class IsStatic (p :: Type -> Type) where

A class for things buildable from static pointers.

GHC wraps each use of the static keyword with fromStaticPtr. Because the static keyword requires its argument to be an instance of Typeable, fromStaticPtr carries a Typeable constraint as well.

Methods

fromStaticPtr :: Typeable a => StaticPtr a -> p a

Instances

IsStatic StaticPtr

Since: base-4.9.0.0

Defined in GHC.Internal.StaticPtr

Methods

fromStaticPtr :: Typeable a => StaticPtr a -> StaticPtr a