Sockets & Inter communication Among Threads

Question

I am using Multithreaded TCP Server. Each socket is created as a separate thread for each client. I would like send data to all clients via send() method of socket. Problem I am facing here is, it sends data to current thread (from which it received) only.

I could not find good documentation for inter thread communication for Python.

Any solution to my problem so that I can send data to all clients.

Thanks.

    #!/usr/bin/env python

    """
    A server with multithreading to handle multiple clients.
    """

    import select
    import socket
    import sys
    import threading
    import logging
    import datetime

    class Server:
        def __init__(self):
            self.host = ''
            self.port = 25000
            self.backlog = 5
            self.size = 1024
            self.server = None

        def open_socket(self):
            try:
                self.server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                self.server.bind((self.host,self.port))
                self.server.listen(5)
                lc.append(self.server)
            except socket.error, (value,message):
                if self.server:
                    self.server.close()
                print "Could not open socket: " + message
                sys.exit(1)

        def run(self):
            self.open_socket()
            input = [self.server,sys.stdin]
            running = 1
            while running:
                inputready,outputready,exceptready = select.select(input,[],[])

                for s in inputready:
                    if s == self.server:
                        c = Client(self.server.accept())
                        c.start()
                        threads.append(c)

            # close all threads
            self.server.close()
            for c in threads:
                c.join()

    class Client(threading.Thread):
        def __init__(self,(client,address)):
            threading.Thread.__init__(self)
            self.client = client
            self.address = address
            self.size = 1024
            dc[address[0]]=client#address[1]
            logging.info('%s added successfully...',address[0])


        def run(self):
            running = 1
            print dc
            while running:
                data = str(self.client.recv(self.size))
                #print dc

                if data.strip() == '0x01':
                    sendtoAll()
                elif data.strip() == '0x02':
                    self.client.send("version"+data)
                elif data.strip() == '0x03':#return current time
                    print datetime.datetime.now()
                    self.client.send(str(datetime.datetime.now()))
                else:
                    self.client.send("empty")
                    #self.client.close()
                    #running = 0
def sendtoAll():
        for i, sock in dc.items():
            print "Address:Sockets = ", i,sock
            try:
                print "sending to %s by Thread "%i
                sock.send("data"+str(threading.current_thread().getName()))
            except socket.error,e:
                print "error socket %s\n" % e
                sock.close()
                del lc[i]

if __name__ == "__main__":
        dc={}       #dict to store ip-address:scokets pair
        lc=[]       #tuples to store all sockets
        threads=[]  #holds threads
        logging.basicConfig(level=logging.INFO)
        logging.info('Starting Server Object...')
        s = Server()
        s.run()

And Client Code is

import socket
import sys

host = '192.168.1.4'
port = 25000
size = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host,port))
sys.stdout.write('%')

while 1:
    # read from keyboard
    line = sys.stdin.readline()
    if line == '\n':
        break
    s.send(line)
    data = s.recv(size)
    sys.stdout.write(data)
    sys.stdout.write('\n%')
s.close()

Answer 1

A TCP socket is one of two endpoints. There is no such thing as "broadcast" in TCP. If you want to send a single message to all your clients, you will have to send it to every one of them individually.

If you use a suitable container for all your client objects, it shoudl "just" be a matter of iterating across this, sending your message to each one.

Answer 2

You could make your threads objects (if any) iterable and you make a "broadcast" function that just iterate through your threads and use their sockets to send the information.

Or if you don't have an object per threads you can always just have a list of sockets and do pretty much the same thing.

Make sure that you use locks correctly based on your needs (Either for all the socket or each individual sockets)