Hello, Whilst experimenting with concurrency and a library which expects me to use the usual event loop I wrote some test code like this.. main :: IO () main = do forkIO forked loop -- Main Loop loop :: IO () loop = do maybeEvent <- pollEvent -- non-blocking case maybeEvent of Just event -> do dispatch event loop Nothing -> do threadDelay 10000 -- 10000 uS = 10 mS loop -- Concurrent thread for test purposes forked :: IO () forked = do threadDelay 1000000 -- 1000000 uS (= 1 S) putStrLn "Hello" forked The idea is to stop a Haskell prog with no runable threads or events to process hogging CPU time. I was a bit dissapointed to find that despite this on my (otherwise idle) machine the above code was still using 96% of cpu time. But fiddling about a bit I found that by changing the thread delay in the main loop to 20 mS the CPU usage dropped to 1% or so, which is much more acceptable (well it did say 1/50 th second accuracy in the docs :-). So this all seems OK, but I wonder if this is a reliable solution on all platforms ghc is ported to (given the the consequence of getting this wrong can be a very greedy program). Is the 20 mS resolution figure a function of ghc only? Or might it depend on other factors too (like OS). Or might it change with ghc version? I think it would nice to have some reliable way to ensure that in reality the thread delay will be as small as possible, but always greater than zero. Maybe a threadDelayResolution constant could be provided? Also, assuming that currently the (hypothetical) threadDelayResolution is 20000 and that in reality the actual threadDelay is N*20000 where N is an integer, I think the docs for threadDelay should specify how N is calculated from the argument of threadDelay. At the moment chosing a thread delay of 19999 sends my CPU usage right back up to 96%, though whether that's as specified or merely a property of ghc 6.2 under Redhat 9 seems a little ambiguous :-) BTW, the docs for Control.Concurrent mention something about an -i<n> RTS option, but I can't find any info on this in the user guide. When I try it I get an error, listing all RTS options. There's no -i listed but there is something that looks related, a -C option, but this doesn't appear in the ghc user guide either :-( Regards -- Adrian Hey