CODEWITHSUNDEEP
multithreadingpython-3.xwebsocketshared-memory
Pithikos
Pithikos

Reputation: 20300

Can't share variable between threads with websockify

I have been fighting with Websockify the last days trying to make it work. There is no apparent documentation so I end up doing things with trial & error.

I have a server which runs on two threads. One thread always sends and receives information while the second thread does other work. However I can't seem to make the two threads talk with each other.

#!/usr/bin/env python

from websocket import WebSocketServer
from threading import Thread
from time import sleep

class Server(WebSocketServer):

    a=10

    def new_client(self):
        while True:
            sleep(1)
            print("Thread 2:    ", self.a)

server = Server('', 9017)
Thread(target=server.start_server).start()

# Main thread continues
while 1:
   sleep(1)
   server.a+=2
   print("Main thread: ", server.a)

Output:

Main thread:  18
Thread 2:     16
Main thread:  20
Thread 2:     16
Main thread:  22
Thread 2:     16
Main thread:  24
Thread 2:     16

Obviously the two threads don't share the same attribute a. Why?

Upvotes: 1

Views: 205

Answers (1)

kanaka
kanaka

Reputation: 73187

By default websockify spawns a new process for each new client connection (websockify connections tend to be long-lived so the process creation overhead isn't generally an issue). This provides some security isolation to reduce the risk that bugs in websockify can be exploited to allow one client to listen in or otherwise affect other client connections.

You can find the process creation code in the top_new_client method. There is an option called --run-once that will handle the a single client in the same process. However, it is designed to exit the main loop in top_new_client after a single connection. You could remove the break statement in the self.run_once conditional check but it means you won't be able to connect more than one client at a time, but perhaps that is sufficient for what you are trying to do.

I also have some unpushed in-progress code to switch WebSocketServer to be more like the HTTPServer class where you provide your own threading or multiprocessing mixin. If you think that might help, let me know and I can push that out to a branch.

Another option for your case would be to use some form of IPC communication to communicate between each client process and the parent process.

Upvotes: 1

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