Cleanup zmq

#Respond with final error message if any, close sockets, and terminate context
def clean_up(manager_name, exit_level, error_message):
    global context, frontend, backend
    print ("%s: closing sockets.... then exiting" % manager_name)
    if (error_message != ""):
        data = "%s" % str(error_message)
        frontend.send_multipart([b"error", data.encode()])

    #Todo: maybe wrap this in a try/except
    frontend.close()
    backend.close()
    context.term()

    sys.exit(exit_level)

#Signal handler
def receive_signal(signum, stack):
    #Todo: mask interrupts
    print ("Interrupt Handler: received interrupt")
    #Do not send an error messaage because we are exiting abnormally
    clean_up("Interrupt Handler", 1, "")

#Register signal handler with signals
def register_signals():
    signal.signal(signal.SIGINT, receive_signal)
    signal.signal(signal.SIGTERM, receive_signal)
    signal.signal(signal.SIGHUP, receive_signal)