Is it safe to call getProcessExitCode more than once?
simons at cryp.to
Sat Oct 30 08:37:19 EDT 2004
Glynn Clements writes:
> Although, depending upon the OS, setting SIGCHLD to
> SIG_IGN may cause processes to be reaped automatically
> (i.e. not become zombies), so that's a possible
I think I've got it under control now. I'm using this
wrapper to make sure there are no unwaited-for child
type ExternHandle = MVar (Handle, Handle, Handle, ProcessHandle)
-- |Run an external process and store its handle in an
-- 'MVar' with a finalizer attached to it that will close
-- the handles and kill the process when the MVar falls out
-- of scope.
extern :: FilePath -> [String] -> IO ExternHandle
extern path args = do
r <- runInteractiveProcess path args (Just "/") (Just )
mv <- newMVar r
addMVarFinalizer mv (catch (cleanup r) (const (return ())))
cleanup (hin, hout, herr, pid) = do
terminateProcess pid >> safeWaitForProcess pid
hClose hin >> hClose hout >> hClose herr
-- |Wait 10 seconds max. If the process hasn't terminated by
-- then, throw an exception. If the child process has been
-- terminated by a signal, return @ExitFailure 137 at . This is
-- a kludge. So it will probably be in here forever.
safeWaitForProcess :: ProcessHandle -> IO ExitCode
safeWaitForProcess pid =
timeout maxwait loop >>= maybe badluck return
loop = catch loop' (\_ -> return (ExitFailure 137))
loop' = wait >> getProcessExitCode pid >>= maybe loop' return
wait = threadDelay 1000000 -- 1/10 second
maxwait = 10000000 -- 10 seconds
badluck = fail "timeout while waiting for external process"
It's ugly, but it seems to work.
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