CODEWITHSUNDEEP
pythonsocketsudplistener
dingerjunkie
dingerjunkie

Reputation: 31

Python overlapping timer with UDP listener

I'm looking for insight on including a timer with/within the WHILE loop of a UDP listener service. The service is part of a device auto-discovery system I need to interact with.

The process requiring the listener has three requirements/responsibilities:

Each of these tasks alone are no problem, and the first two are easy to include. What I'm not comfortable with is "interrupting the listener" or modifying the WHILE loop of the listener to send the "alive" packet.

If I "wait" for the interval, I suspend other processes. Will a Scheduler object do the same, or allow us to continue? I can't multi-thread, because I need to receive and send on a specific port, which is bound within the thread.

here is what I have...

import time
import socket
import sys 
import shutil
import signal
import string
import re
import os
import socket
import fcntl
import struct

HOST = ''
PORT = 8888
RESPONSE_MSG = 'Yes, I'm here'
ALIVE_MSG = 'I'm alive'
IDENTIFY_MSG = 'It's me'
IP_ADDR = ''
INTERVAL = 1800

# Datagram (udp) socket
try :
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    print 'Socket created'
except socket.error, msg :
    print 'Failed to create socket. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
    sys.exit() 

try:
    s.bind((HOST, PORT))
except socket.error , msg:
    print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
    sys.exit()

# broadcast wake-up message
s.sendto(IDENTIFY_MSG,'239.255.255.250')

#now keep listening...how do I not stop listening while sending a packet on an interval?
while 1:
    # receive data from client (data, addr)
    d = s.recvfrom(1024)
    data = d[0]
    source_addr = d[1]

    if not data: 
        break

    s.sendto(RESPONSE_MSG, source_addr)

Upvotes: 2

Views: 793

Answers (1)

dingerjunkie
dingerjunkie

Reputation: 31

I think I have what is a working solution. It "punts" on the looping complexity a bit, but I believe it is a clean, maintainable, readable solution.

I've created three specific .py scripts; one opens a socket to send the "wake-up" packet, second opens a socket to send the "alive" packet, and a third that opens up a socket to listen/respond to device search requests.

These are then imported into a "calling script" with a timer-based interrupt.

Here's how it looks...

import udp_wakeup
import udp_listen
import udp_alive
import shutil
import string
from threading import Timer
import thread, time, sys
from datetime import datetime as dt

#dummy flag to ensure constant looping
restart = 1

def timeout():
    thread.interrupt_main()

#Call and execute the wake-up packet broadcast
udp_wakeup.main()

#Initiate timer for 1800 seconds, or 30 minutes
while restart = 1
  try:
    #Call and execute the listener routine
    Timer(1800, timeout).start()
    udp_listen.main()
  except:
    #On Timer expire, break from listener, call Alive-broadcast, reset timer and restart listener
    udp_alive.main()

Upvotes: 1

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