Does not work with async exceptions

[ndmitchell]

Given the code Proc.hs:

import System.Process
import System.Time.Extra

main = do
    (t, e) <- duration $ timeout 2 $ system "sleep 5s"
    print (showDuration t, e)
    (t, e) <- duration $ timeout 2 $ do
        (_, _, _, pid) <- createProcess (proc "sleep" ["5s"])
        waitForProcess pid
    print (showDuration t, e)
    (t, e) <- duration $ timeout 2 $ do
        withCreateProcess (proc "sleep" ["5s"]) $ \_ _ _ pid -> waitForProcess pid
    print (showDuration t, e)

I observe:

C:\Neil\temp>ghc Proc.hs -package=process-1.6.2.0 && proc
[1 of 1] Compiling Main             ( Proc.hs, Proc.o )
Linking Proc.exe ...
("5.06s",Just ExitSuccess)
("5.05s",Just ExitSuccess)
("5.04s",Just ExitSuccess)

C:\Neil\temp>ghc Proc.hs -package=process-1.6.2.0 -threaded && proc
[1 of 1] Compiling Main             ( Proc.hs, Proc.o )
Linking Proc.exe ...
("5.48s",Nothing)
("5.49s",Nothing)
proc: terminateProcess: permission denied (Permission denied)

Running Windows 10, 64bit GHC 8.2.1, process 1.6.2.0. Requires the extra library to be installed and the sleep binary to be on %PATH%. I would expect all these functions to die around 2s, but none of the timeouts are effective.

Originally found when debugging an upstream bug in Shake: ndmitchell/shake#538

[nh2]

Possibly related to https://ghc.haskell.org/trac/ghc/ticket/8684?

That one is about not being able to timeout hWaitForInput, but it's possible that waitpid() also should be interruptible.

[simonmar]

This relies on the interruptible extension to the FFI to allow the wait to be interrupted by the async exception. See https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ffi-chap.html#interruptible-foreign-calls

It works on Linux (I just checked), but perhaps not Windows. I don't remember off hand whether it is supposed to work or not.