#8972: Investigate adding fast compare-and-swap Int type/primops ------------------------------------+------------------------------------- Reporter: tibbe | Owner: tibbe Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I've received reports that using `IORef Int` and `atomicModifyIORef` to implement an atomic counter in the ekg package has become a bottleneck for some of its users. These users update the counter thousands of times per second, using multiple threads. I will investigate whether adding a dedicated atomic `Int` reference type will offer significant speed improvements. Such a type can also be used to implement cheaper locks (by using bits in the int to represent different lock states, such as reader/write locks.) Lets call this new type `AtomicIntRef` for now. This new type needs to support at least these functions: {{{#!haskell add :: AtomicIntRef -> Int -> IO Int set :: AtomicIntRef -> Int -> IO () get :: AtomicIntRef -> IO Int }}} `add` would be implemented using the `lock` and `xaddq` instructions. `set` and `get` are just simple loads and stores on x86, as these are atomic. We might also want to consider having other functions, such as a `cas`. Furthermore, there are subtleties with memory barriers that might motivate having barrier/barrier-less versions of some functions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8972 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler