Tracking application launched with a python file

Question

I've encountered a situation where I thought it would be a good idea to create a launcher for an application which I tend to run several instances of. This is to ensure that I and the application get access to the wanted environment variables that can be provided and set for each instance.

import os
import subprocess


def launch():
    """
    Launches application.
    """
    # create environment
    os.environ['APPLICATION_ENVIRON'] = 'usr/path'

    # launch application
    application_path = 'path/to/application'
    app = subprocess.Popen([application_path])
    pid = app.pid
    app.wait()

    print 'done with process: {}'.format(pid)


if __name__ == '__main__':
    launch()

I want to be able to track the applications, do I dump the pids in a file and remove them when the process closes? Do I launch a service that I communicate with?

Being fairly new to programming in general I don't know if I'm missing a term in the lingo or just thinking wrong. But I was reading up on Daemons and services to track the applications and couldn't come up with a proper answer. Put simply, a bit lost how to approach it.

Answer 1

What you're doing already seems reasonable. I'd probably extend it to something like this:

import os
import subprocess


def launch_app():
    os.environ['APPLICATION_ENVIRON'] = 'usr/path'
    application_path = 'path/to/application'
    return subprocess.Popen([application_path])


def _purge_finished_apps(apps):
    still_running = set()
    for app in apps:
        return_code = app.poll()
        if return_code is not None:
            print "  PID {} no longer running (return code {})".format(app.pid, return_code)
        else:
            still_running.add(app)
    return still_running


def ui():
    apps = set()

    while True:
        print
        print "1. To launch new instance"
        print "2. To view all instances"
        print "3. To exit, terminating all running instances"
        print "4. To exit, leaving instances running"
        opt = int(raw_input())

        apps = _purge_finished_apps(apps)

        if opt == 1:
            app = launch_app()
            apps.add(app)
            print "  PID {} launched".format(app.pid)

        elif opt == 2:
            if not apps:
                print "There are no instances running"
            for app in apps:
                print "  PID {} running".format(app.pid)

        elif opt == 3:
            for app in apps:
                print "Terminating PID {}".format(app.pid)
                app.terminate()
            for app in apps:
                app.wait()
                print "PID {} finished".format(app.pid)
            return

        elif opt == 4:
            return


if __name__ == "__main__":
    ui()