Run or Raise using DBus

activate_app_if_running.py

"""
Allow an application to activate a running instance of itself instead of
starting another instance.
"""
## Usage ##
# import sys
# APP_ID = "com.example.application"
# if activate_if_already_running(APP_ID):
#     sys.exit(0)
# 
# def activateHandler():
#     print "I was activated!"
# listen_for_activation(APP_ID, activateHandler)

import dbus.service
from dbus.mainloop.glib import DBusGMainLoop

def listen_for_activation(app_id, activateHandler):
    """
    Listen for 'activate' events. If one is sent, call 'activate'.
    """
    class DBUSService(dbus.service.Object):
        def __init__(self, activateHandler):
            self.activateHandler = activateHandler
            
            bus_name = dbus.service.BusName(app_id, bus=dbus.SessionBus())
            dbus.service.Object.__init__(self, bus_name, '/' + app_id.replace('.', '/'))
    
        @dbus.service.method(app_id)
        def activate(self):
            self.activateHandler()
    
    DBusGMainLoop(set_as_default=True)
    _myservice = DBUSService(activateHandler)

def activate_if_already_running(app_id, appName):
    """
    Activate the existing application if it's already running. Return True if found
    an existing application, and False otherwise.
    """
    bus = dbus.SessionBus()
    try:
        programinstance = bus.get_object(app_id, '/' + app_id.replace('.', '/'))
        activate = programinstance.get_dbus_method('activate', app_id)
    except dbus.exceptions.DBusException:
        return False
    else:
        print "An existing instance of " + appName + " is already running. Activating it."
        activate()
        return True
    finally:
        bus.close()