Am Samstag 17 April 2010 14:41:28 schrieb Simon Peyton-Jones:
> I have not been following the details of this, I'm afraid, but I notice
this:
> > forever' m = do _ <- m
> > forever' m
>
> When I define that version of forever, the space leak goes away.
>
> What was the old version of forever that led to the leak?
Control.Monad.forever
forever :: Monad m => m a -> m b
forever m = m >> forever m
However, that isn't the problem. In my tests, both variants of forever
exhibit the same behaviour, what makes it leak or not is the optimisation
level.
>
> If you can boil down the leak to a simple test case, do submit a Trac
> ticket.
>
> Simon
The code below behaves well if compiled without optimisations (~36K maximum
residency).
When compiled with optimisations (-O1 or -O2, no discernible difference),
it gets stuck in the infinite loop "always (return ())" [no surprise], but
it runs in small space (+RTS -M58K for me).
With -O2 -fno-state-hack (or -O1 -fno-state-hack), it leaks memory:
469,292,260 bytes allocated in the heap
837,326,332 bytes copied during GC
233,727,956 bytes maximum residency (9 sample(s))
3,740,036 bytes maximum slop
456 MB total memory in use (4 MB lost due to fragmentation)
---------------------------------------------
module Main (main) where
import Control.Concurrent
{-
always :: Monad m => m a -> m b
always a = a >> always a
-}
always :: Monad m => m a -> m b
always a = do
_ <- a
always a
spawner :: IO ()
spawner = always $ do
forkIO $ always (return ())
putStrLn "Delaying"
threadDelay 1000000
main :: IO ()
main = do
putStrLn "Spawning"
forkIO spawner
putStrLn "Delaying main"
threadDelay 4000000
-------------------------------------------
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