Don Stewart wrote:
dvde:
Don Stewart schrieb:
It is not possible to write a modifyIORef that *doesn't* leak memory!
Why? Or can one read about it somewhere?
Try writing a version of this program, using modifyIORef only, such that it doesn't exhaust the heap:
import Data.IORef import Control.Monad import System.IO.Unsafe
ref :: IORef Int ref = unsafePerformIO $ newIORef 0 {-# NOINLINE ref #-}
main = do modifyIORef ref (\a -> a + 1) main
Run it in a constrained environment, so you don't thrash:
$ ./A +RTS -M100M Heap exhausted; Current maximum heap size is 99999744 bytes (95 MB); use `+RTS -M<size>' to increase it.
The goal is to run in constant space.
-- Don _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Thanks, that's good to know. do x <- readIORef ior writeIORef ior $! (x+1) Works for me. The laziness of modifyIORef and workarounds would be a good thing to have documented in the modifyIORef docs [1], since it's probably a common source of memory leaks. I'd also be in favor of a strict version of modifyIORef. [1] http://www.haskell.org/ghc/dist/current/docs/libraries/base/Data-IORef.html#... -jim