Skip to content

Process package

The Process package provides support for handling Unix style processes. For each external process that you want to handle, you need to create a ProcessMonitor and a corresponding ProcessNotify object. Each ProcessMonitor runs as it own actor and upon receiving data will call its corresponding ProcessNotify's method.

Example program

The following program will spawn an external program and write to it's STDIN. Output received on STDOUT of the child process is forwarded to the ProcessNotify client and printed.

use "process"
use "files"

actor Main
  new create(env: Env) =>
    // create a notifier
    let client = ProcessClient(env)
    let notifier: ProcessNotify iso = consume client
    // define the binary to run
      let path = FilePath(env.root as AmbientAuth, "/bin/cat")?
      // define the arguments; first arg is always the binary name
      let args: Array[String] val = ["cat"]
      // define the environment variable for the execution
      let vars: Array[String] val = ["HOME=/"; "PATH=/bin"]
      // create a ProcessMonitor and spawn the child process
      let auth = env.root as AmbientAuth
      let pm: ProcessMonitor = ProcessMonitor(auth, auth, consume notifier,
      path, args, vars)
      // write to STDIN of the child process
      pm.write("one, two, three")
      pm.done_writing() // closing stdin allows cat to terminate
      env.out.print("Could not create FilePath!")

// define a client that implements the ProcessNotify interface
class ProcessClient is ProcessNotify
  let _env: Env

  new iso create(env: Env) =>
    _env = env

  fun ref stdout(process: ProcessMonitor ref, data: Array[U8] iso) =>
    let out = String.from_array(consume data)
    _env.out.print("STDOUT: " + out)

  fun ref stderr(process: ProcessMonitor ref, data: Array[U8] iso) =>
    let err = String.from_array(consume data)
    _env.out.print("STDERR: " + err)

  fun ref failed(process: ProcessMonitor ref, err: ProcessError) =>

  fun ref dispose(process: ProcessMonitor ref, child_exit_status: ProcessExitStatus) =>
    let code: I32 = consume child_exit_code
    match child_exit_status
    | let exited: Exited =>
      _env.out.print("Child exit code: " + exited.exit_code().string())
    | let signaled: Signaled =>
      _env.out.print("Child terminated by signal: " + signaled.signal().string())

Process portability

The ProcessMonitor supports spawning processes on Linux, FreeBSD, OSX and Windows.

Shutting down ProcessMonitor and external process

When a process is spawned using ProcessMonitor, and it is not necessary to communicate to it any further using stdin and stdout or stderr, calling done_writing() will close stdin to the child process. Processes expecting input will be notified of an EOF on their stdin and can terminate.

If a running program needs to be canceled and the ProcessMonitor should be shut down, calling dispose will terminate the child process and clean up all resources.

Once the child process is detected to be closed, the process exit status is retrieved and ProcessNotify.dispose is called.

The process exit status can be either an instance of Exited containing the process exit code in case the program exited on its own, or (only on posix systems like linux, osx or bsd) an instance of Signaled containing the signal number that terminated the process.

Public Types