Data.Atomics.Internal

This module provides only the raw primops (and necessary types) for atomic operations.

Documentation

casIntArray# :: MutableByteArray# s -> Int# -> Int# -> Int# -> State# s -> (#State# s, Int##)

fetchAddIntArray# :: MutableByteArray# s -> Int# -> Int# -> State# s -> (#State# s, Int##)

readForCAS# :: MutVar# RealWorld a -> State# RealWorld -> (#State# RealWorld, Ticket a#)

casMutVarTicketed# :: MutVar# RealWorld a -> Ticket a -> Ticket a -> State# RealWorld -> (#State# RealWorld, Int#, Ticket a#)

casArrayTicketed# :: MutableArray# RealWorld a -> Int# -> Ticket a -> Ticket a -> State# RealWorld -> (#State# RealWorld, Int#, Ticket a#)

Unsafe, machine-level atomic compare and swap on an element within an Array.

type Ticket a = Any a

When performing compare-and-swaps, the ticket encapsulates proof that a thread observed a specific previous value of a mutable variable. It is provided in lieu of the old value to compare-and-swap.

Design note: Tickets exist to hide objects from the GHC compiler, which can normally perform many optimizations that change pointer equality. A Ticket, on the other hand, is a first-class object that can be handled by the user, but will not have its pointer identity changed by compiler optimizations (but will of course, change addresses during garbage collection).