Permission denied error with runProcess/openFile

Given this program:

module Main() where

import Control.Concurrent
import System.IO
import System.Process

main = do
    hSetBuffering stdout NoBuffering
    forkIO $ f "foo1.txt"
    forkIO $ f "foo2.txt"
    threadDelay $ 100*1000000
    putStrLn "Finished successfully"

f file = do
    h <- openFile file AppendMode
    hPutStrLn h "fakdjsklj"
    putChar '.'
    pid <- runProcess "sh" ["-c","sleep 0.1s"] Nothing Nothing Nothing (Just h) (Just h)
    waitForProcess pid
    f file

Running under Cygwin, in GHC 6.10.2, I get:

$ runhaskell Test.hs
..Test.hs: foo1.txt: openFile: permission denied (Permission denied)

It shouldn't - the openFile calls should always succeed. This bug is a reduced test case from a real system, which I papered over with:

retryIO :: IO a -> IO a
retryIO act = catchIO act $ \x -> do
    threadDelay $ 1 * 1000000 -- 1 second
    performGC
    act

Now calling retryIO $ openFile ... works reliably. These problems are occurring sufficiently often that retryIO is about to go in to our standard library :-)

This may be related to #2924 (closed), but has the advantage of replicating easily.

Trac metadata

Trac field	Value
Version	6.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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