atomic-primops- A safe approach to CAS and other atomic ops in Haskell.

Safe HaskellNone



This should be the most efficient implementation of atomic counters. You probably don't need the others! (Except for testing/debugging.)



data AtomicCounter Source

The type of mutable atomic counters.

type CTicket = IntSource

You should not depend on this type. It varies between different implementations of atomic counters.

newCounter :: Int -> IO AtomicCounterSource

Create a new counter initialized to the given value.

readCounterForCAS :: AtomicCounter -> IO CTicketSource

Just like the Data.Atomics CAS interface, this routine returns an opaque ticket that can be used in CAS operations. Except for the difference in return type, the semantics of this are the same as readCounter.

peekCTicket :: CTicket -> IntSource

Opaque tickets cannot be constructed, but they can be destructed into values.

writeCounter :: AtomicCounter -> Int -> IO ()Source

Make a non-atomic write to the counter. No memory-barrier.

casCounter :: AtomicCounter -> CTicket -> Int -> IO (Bool, CTicket)Source

Compare and swap for the counter ADT. Similar behavior to casIORef, in particular, in both success and failure cases it returns a ticket that you should use for the next attempt. (That is, in the success case, it actually returns the new value that you provided as input, but in ticket form.)

incrCounter :: Int -> AtomicCounter -> IO IntSource

Increment the counter by a given amount. Returns the value AFTER the increment (in contrast with the behavior of the underlying instruction on architectures like x86.)

Note that UNLIKE with boxed implementations of counters, where increment is based on CAS, this increment is O(1). Fetch-and-add does not require a retry loop like CAS.

incrCounter_ :: Int -> AtomicCounter -> IO ()Source

An alternate version for when you don't care about the old value.