CODEWITHSUNDEEP
pythonmultithreadingpython-2.7backgroundudp
Ricardo Martinez Muñoz
Ricardo Martinez Muñoz

Reputation: 51

Receive UDP packets in background (PYTHON)

I want to have a thread that waits for a UDP packet in background and while the packet is not received I want the script be able to do another things. But when I start the thread the script waits for an UDP packet and stop.

import threading
import socket


def rec_UDP():
    while True:
        # UDP commands for listening
        UDP_PORT = 5005
        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        sock.bind(('10.0.0.15', UDP_PORT))
        data, addr = sock.recvfrom(1024)
        print "received message:", data
        return data


# The thread that ables the listen for UDP packets is loaded
listen_UDP = threading.Thread(target=rec_UDP())
listen_UDP.start()

data = 'Nothing received'

while True:
    print 'The packet received is: ' + data

Upvotes: 5

Views: 8832

Answers (2)

M61Vulcan
M61Vulcan

Reputation: 337

This doesn't work for Python 3, but it set me on the right path. here's my Python 3 version.

#!/usr/bin/python3

import _thread, time, socket

data = ''   # Declare an empty variable
# UDP setup for listening
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(('', 12345))  # I'm using port 12345 to bind to

# Define a function for the thread
def listening_thread():
    global data     # data needs to be defined as global inside the thread
    while True:
        data_raw, addr = sock.recvfrom(1024)
        data = data_raw.decode()    # My test message is encoded
        print ("Received message inside thread:", data)

try:
   _thread.start_new_thread(listening_thread, ())
except:
    print ("Error: unable to start thread")
    quit()


while 1:
    print ('Now I can do something useful while waiting in the main body.')
    if data:
        print ('THE PACKET RECEIVED BY THE MAIN BODY IS: ' + data)
        data = ''   # Empty the variable ready for the next one
    time.sleep(2)

Upvotes: 1

falsetru
falsetru

Reputation: 369274

By appending () after the function, the code calls the function directly and therefore blocking the main thread instead of running the function in a separated thread.

Remove the () after the function name.

listen_UDP = threading.Thread(target=rec_UDP)

Upvotes: 3

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