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

2012-10-19 Thread Jason Dusek 
2012/10/19 Donn Cave d...@avvanta.com:
 Quoth Jason Dusek jason.du...@gmail.com,

 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

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

2012-10-18 Thread Gwern Branwen 
On Thu, Oct 18, 2012 at 5:03 PM, Jason Dusek jason.du...@gmail.com wrote:
 For diagnostic purposes, I'd like to print the PID of the
 process attached to this handle -- how best to do that?

In Mueval when I wanted the PID (so I could later send sigkills), I did this:

  hdl - runProcess mueval-core args Nothing Nothing Nothing
Nothing Nothing
  _ - forkIO $ do
 threadDelay (7 * 70)
 status - getProcessExitCode hdl
 case status of
 Nothing - do terminateProcess hdl
   _ - withProcessHandle hdl (\x
- case x of

OpenHandle pid - signalProcess 9 pid  return (undefined, undefined)

_ - return (undefined,undefined))
   exitWith (ExitFailure 1)
 Just a - exitWith a
  stat - waitForProcess hdl
  exitWith stat

The key is the poorly documented withProcessHandle ::
System.Process.Internals.ProcessHandle - (ProcessHandle__ - IO
(ProcessHandle__, a)) - IO a

The implementation:

data ProcessHandle__ = OpenHandle PHANDLE | ClosedHandle ExitCode
type PHANDLE = CPid

Well, my code seems to work, anyway...

-- 
gwern
http://www.gwern.net

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

2012-10-18 Thread Donn Cave 
Quoth Jason Dusek jason.du...@gmail.com,

 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.

Donn



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