#8345: A more efficient atomicModifyIORef' -------------------------------------+------------------------------------- Reporter: parcs | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: | Version: 7.6.3 libraries/base | Keywords: IORef Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Moderate (less Unknown/Multiple | than a day) Type of failure: Runtime | Blocked By: performance bug | Related Tickets: #5926 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): It looks like my fears were unjustified. If I run this: {{{#!hs silly = \current -> (True, True) {-# INLINE flipper #-} stupid = newIORef False >>= \r -> let flop = atomicModifyIORef' r silly in forever flop main = do flippy <- forkIO stupid mapM_ print [x | x <- [1..], x `rem` 10000000 == 0] }}} with just one thread, and try either of the above implementations, it prints things just fine. I don't see any obvious signs of allocation anywhere in the `stupid` thread, so I would speculate that maybe `atomicModifyMutVar#` always gives the scheduler a go. This looks like a real good catch by parcs. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8345#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler