Example of a script being able to hand-over to a second instance of itself

handover.py

"""
Python `hand-over` strategy example
"""
import os
import sys
import socket

SOCKFILE = "/tmp/handover.sock"

# Check for this script already running
# by trying to receive one byte of data over the socket
try:
    client = socket.socket(socket.AF_UNIX,
                           socket.SOCK_STREAM)
    client.connect(SOCKFILE)
    client.recv(1)
except socket.error:
    pass

# Remove socket if already exists since now we are
# the only code that runs after the previous check
if os.path.exists(SOCKFILE):
    os.remove(SOCKFILE)

# Recreate socket
server = socket.socket(socket.AF_UNIX,
                       socket.SOCK_STREAM)
server.bind(SOCKFILE)
server.listen(5)
server.setblocking(False)

def heavylifting():
    """ Main task to run within this application
    """
    i = 0
    while True:
        print("Doing some work, count to {}".format(i))
        i += 1

        # Handover check
        try:
            # Try to send data over the socket
            conn = server.accept()[0]
            conn.close()
            break
        except socket.error:
            # Other end of socket not connected,
            # continue looping
            pass

# Run the main task in a loop
heavylifting()

###
# Release resources for handover:
# * Close file handles
# * Close serial port
# * ...
#
# In the real application finally create this file
# to signal being ready to retire:
# open('/data/resin-kill-me', 'w+').close()
###

# Exit
# Force exit all threads
sys.exit(0)