Re: [Haskell-cafe] Getting PID of a child process

2012/10/19 Donn Cave :

Quoth Jason Dusek ,

...

Using `System.Process.runInteractiveProcess', I can start a process and get a handle to it:

runInteractiveProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> IO (Handle, Handle, Handle, ProcessHandle)

For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that?

There's a good chance this isn't the best way, but it seems to work:

import System.Process import System.Process.Internals (ProcessHandle__(..), PHANDLE, withProcessHandle)

-- for use with withProcessHandle getPID :: ProcessHandle__ -> IO (ProcessHandle__, Maybe PHANDLE) getPID h@(OpenHandle t) = return (h, Just t) getPID h@(ClosedHandle t) = return (h, Nothing)

main = do (h0, h1, h2, hp) <- runInteractiveProcess "/bin/date" [] Nothing Nothing mp <- withProcessHandle hp $ getPID print mp

Seems like more scaffolding than this application really ought to require.

It seems wrong that in the definition of ProcessHandle__, the PID is not recoverable once the process has exited. I wonder if this has something to do with Windows compatibility. -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B