Using Processes as Threads with Networking in Python

Question

Basically, my idea was to write some sort of basic server where I could connect to my computer and then run a command remotely. This didn't seem to be much of a problem; but then I had the bright idea that the next step would logically be to add some sort of threading so I could spawn multiple connections.

I read that, because of the GIL, multiprocessing.Process would be the best to try to do this. I don't completely understand threading and it's hard to find good documentation on it; so I'm kind of just throwing stuff and trying to figure out how it works.

Well, it seems like I might be close to doing this right; but I have a feeling I'm just as likely to be no where near doing this correctly. My program now does allow multiple connections, which it didn't when I first started working with threading; but once a connection is established, and then another is established, the first connection is no longer able to send a command to the server. I would appreciate it if someone could give me any help, or point me in the right direction on what I need to learn and understand.

Here's my code:

class server:
    def __init__(self):
        self.s = socket.socket()
        try:
            self.s.bind(("",69696))
            self.s.listen(1)
        except socket.error,(value,message):
            if self.s:
                self.s.close()
    def connection(self):
        while True:
            client , address = self.s.accept()

            data = client.recv(5)
            password = 'hello'
            while 1:
                if data == password:
                    subprocess.call('firefox')
                    client.close()
                else:
                    client.send('wrong password')
                    data = client.recv(5)
            p = Process(target=x.connection())
            p.start()
x = server()

if __name__ == '__main':
    main()

PS: That while 1: loop is going to go on infinitely if the condition data == password is true. It will just keep on spawning firefox processes ad-infinitum. You may want to add a break after client.close() — entropy
– entropy, Commented Mar 4, 2013 at 23:27
Mainly I've been trying it out on Linux/Ubuntu, but I did try it on my VirtualBox Windows 7 also. — Russ Adams
– Russ Adams, Commented Mar 4, 2013 at 23:29
And yeah, I know, the reason I added that was to make sure I could check whether or not I was getting disconnected for the right reasons or not. Or well, the reason I wanted to be getting disconnected for, if that makes sense. I didn't think about adding break though, will do. — Russ Adams
– Russ Adams, Commented Mar 4, 2013 at 23:30
Consider twistedmatrix.com to avoid having to solve a number of boring problems related to writing network applications. — Jean-Paul Calderone
– Jean-Paul Calderone, Commented Mar 4, 2013 at 23:52

entropy · Accepted Answer · 2013-03-04 23:44:04Z

1

Well, this answer only applies if you're on a unix or unix-like operating system(windows does not have os.fork() which we use).

One of the most common approaches for doing these things on unix platforms is to fork a new process to handle the client connection while the master process continues to listen for requests.

Below is code for a simple echo server that can handle multiple simultaneous connections. You just need to modify handle_client_connection() to fit your needs

import socket
import os

class ForkingServer:
    def serve_forever(self):
        self.s = socket.socket()
        try:
            self.s.bind(("", 9000))
            self.s.listen(1)
        except socket.error, (value,message):
            print "error:", message
            if self.s:
                self.s.close()
            return

        while True:
            client,address = self.s.accept()
            pid = os.fork()
            # You should read the documentation for how fork() works if you don't
            # know it already
            # The short version is that at this point in the code, there are 2 processes
            # completely identical to each other which are simulatenously executing
            # The only difference is that the parent process gets the pid of the child
            # returned from fork() and the child process gets a value of 0 returned
            if pid == 0:
                # only the newly spawned process will execute this
                self.handle_client_connection(client, address)
                break
            # In the meantime the parent process will continue on to here
            # thus it will go back to the beginning of the loop and accept a new connection

    def handle_client_connection(self, client,address):
        #simple echo server
        print "Got a connection from:", address
        while True:
            data = client.recv(5)
            if not data:
                # client closed the connection
                break
            client.send(data)
        print "Connection from", address, "closed"


server = ForkingServer()
server.serve_forever()

answered Mar 4, 2013 at 23:44

entropy

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5 Comments

Russ Adams Over a year ago

The water just gets deeper and deeper! First it was Threading, then it was Process is better, now there's os.fork(). So many choices, how am I supposed to decide what to learn! But thank you though for the response, this works well and seems much less confusing than Threading.

entropy Over a year ago

You can probably achieve the same effect as os.fork() with Process() in a more portable way(since os.fork() does not exist on windows). However, I'm most familiar with os.fork() and it's 2am here so I don't want to go on giving advice about things I have no experience in :)

Russ Adams Over a year ago

I completely understand, it seems good to know os.fork() anyways, it's simple and doesn't come with a lot of baggage. I'll still try to find some good documentation on Process() but for now this is good. Thanks again!

entropy Over a year ago

glad to have been of help :)

Honest Abe Over a year ago

@RussAdams I recommend checking out PyMOTW.

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