On Tue, Jun 17, 2008 at 08:56:31AM -0700, Don Stewart wrote:
dons:
magicloud.magiclouds:
OK. Here it is. I want to make a monitor tool for linux. It runs for a long time, and give out a certain process's io stat per second. The way I get io stat is to read from /proc/pid/io. But the data in this file is a total, I need to read it first, then next second, read it again, and shows the difference, and go on. So, what is your idea?
Easy,
import Control.Concurrent import Control.Monad
main = go 0 where go st = forever $ do n <- read `fmap` readFile "/proc/pid/io" print (n - st) -- display difference threadDelay (10^6)
Oops, not 'forever' :)
go st = do ... go n
or doEverySecond :: (a -> IO a) -> a -> IO () doEverySecond job n = do n' <- job n threadDelay (10^6) doEverySecond job n' showChange :: Int -> IO Int showChange n = do n' <- read `fmap` readFile "/proc/pid/io" print (n' - n) -- display difference return n' main = doEverySecond showChange 0 -- note: prints bogus value first time This demonstrates how you can abstract the ideas in Don's solution just a bit, so that you could reuse these functions for somewhat different purposes. For such a simple function you'd probably be better with Don's solution, but if your monitor tool is starting to look more complicated than this, perhaps you're better off breaking it into different functions. David