Ah, that would be a bug in older ByteString implementations, that were a bit incautious about closing handles. This example works for me with
bytestring-0.9.1.0
Yup, thank you Don and Duncan for pointing this out. I updated my bytestring library and the test case no longer fails. However, I'm still having problems and not sure why. I was able to distill the problem down to this: $ od -x 1word32.bin 0000000 0500 2ca4 $ runhaskell test6.hs loading... saving... test6.hs: 1word32.bin: openFile: resource busy (file is locked) $ cat test6.hs module Main where import Control.Applicative import Control.Parallel.Strategies (rnf, NFData, using) import Data.Binary import qualified Data.ByteString.Lazy.Char8 as B import Data.Word stateFile = "1word32.bin" loadState :: IO Word32 loadState = decode <$> B.readFile stateFile saveState :: Word32 -> IO () saveState db = B.writeFile stateFile $ encode db {- -- Works! loadState = B.readFile stateFile saveState = B.writeFile stateFile -} -- force x = print x >> return x force = return . (`using` rnf) main = do putStrLn "loading..." d <- force =<< loadState putStrLn "saving..." saveState d I tried this both with "print" and "rnf" to the same effect. It looks like there still might be some situations where the file isn't being closed? Should the file be closed when the last byte is read (in this case its definitely reading all four bytes) or when the first byte after that is read (in this case it probably doesn't attempt to read more than 4 bytes)? Tim Newsham http://www.thenewsh.com/~newsham/