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Calling a Process by means of a MailboxProcessor
f#async

I'm attempting, as several others have, to host an fsi process but wanted to do so through a MailboxProcessor. My first question is "Is this a good idea?" The second "What's wrong with my attempt?" I've not used Processes much, so I am likely missing something.

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open System
open System.Diagnostics
open System.IO
open System.Threading

#if INTERACTIVE
#r @"C:\Program Files (x86)\FSharpPowerPack-2.0.0.0\bin\FSharp.PowerPack.dll"
#endif

open Microsoft.FSharp.Control

type ProcessAgent(appPath, out:TextWriter, err:TextWriter) =
  let psi = new ProcessStartInfo(FileName = appPath,
                                 CreateNoWindow = true,
                                 RedirectStandardInput = true,
                                 RedirectStandardOutput = true,
                                 RedirectStandardError = true,
                                 UseShellExecute = false,
                                 ErrorDialog = true)
  let agent = MailboxProcessor.Start(fun inbox ->
    let rec loop () = async {
      let! msg = inbox.Receive()
      let proc = Process.Start(psi)
      let stdOutThread = new Thread(ThreadStart(fun () -> out.WriteLine(proc.StandardOutput.ReadToEnd())), IsBackground = true)
      let stdErrThread = new Thread(ThreadStart(fun () -> err.WriteLine(proc.StandardError.ReadToEnd())), IsBackground = true)
      proc.Start() |> ignore
      stdOutThread.Start()
      stdErrThread.Start()
      let expr = msg + ";;\r\n"
      proc.StandardInput.Write(expr :> obj)
      proc.StandardInput.Flush()
      proc.WaitForExit()
      stdOutThread.Join()
      stdErrThread.Join()
      printfn "Exit code: %A" proc.ExitCode
      printfn "Expression: %s" msg
      proc.Dispose()
      return! loop () }
    loop () )
  member this.Post(msg) = agent.Post(msg)

let fsiPath = Environment.GetFolderPath(Environment.SpecialFolder.ProgramFiles) + "/FSharp-2.0.0.0/bin/fsi.exe"
let output = new StringWriter()
let error = new StringWriter()
let agent = new ProcessAgent(fsiPath, output, error)

agent.Post("printfn \"Hello\"")
printfn "Output: %s" (output.ToString())
printfn "Error: %s" (error.ToString())
Console.ReadKey() |> ignore
printfn "Finished!"

I'm sure someone might point out that I'm creating a new process for each call. I have moved that direction to try to localize the immediate exit problem I'm experiencing. Ideally, I'll have one process handling all requests. I tried starting without the explicit threads and using AsyncReadToEnd. I know you can't get both the output and error streams synchronously. Any other thoughts there? Finally, I was wondering if I'm sniffing up the wrong path? Does fsi output anything to either stream? I'm getting nothing back, and when I tried other command line tools earlier, they were returning things.
Thanks,
Ryan

.

I found an excellent solution in the FAKE (F# Make) project by Steffen Forkmann:

[link:github.com]

[link:github.com]

By on 11/17/2010 6:01 PM ()

ReadToEnd call is blocking, so it will not return until stream is closed from the other side. Try read from output stream by lines or by chars.

By on 9/21/2010 8:23 AM ()

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