RuntimeError: threads can only be started once Python Tkinter webserver

Question

I am trying to create a webserver in python which can be started and stopped using a tkinter GUI. In tkinter I have a button which will call start() and a button that will call stop(). Initially everything works fine, the server starts when I click the button and it also stops when I click the stop button. When I try to restart the server again using the start button, I get a runtime error

RuntimeError: threads can only be started once

I believe it has something to do with the fact that I have already initialized threading in my init, and I can not figure out how to get this to work.

I have read through the threading docs multiple times, but I am struggling to understand it entirely. Any assistance would be greatly appreciated.

Thank you!

import threading
import socketserver
import http.server
import os


class WebServer(object):

    def __init__(self, host, port):
        self.host = host
        self.port = port
        self.handler = http.server.SimpleHTTPRequestHandler
        self.server = socketserver.TCPServer((self.host, self.port), self.handler)
        socketserver.TCPServer.allow_reuse_address = True
        self.server_thread = threading.Thread(target=self.server.serve_forever, name="Server_Thread")
        self.server_thread.setDaemon(True)

    def start(self):
        web_dir = os.path.join(os.path.dirname(__file__), 'www')
        os.chdir(web_dir)
        self.server_thread.start()

    def stop(self):
        os.chdir('..')
        self.server.shutdown()
        self.server.server_close()

Vladimir Poghosyan Vladimir Poghosyan · Accepted Answer · 2018-08-09T14:16:27

As the python documentation states, the start method of the Thread object can only be called once.

In your case, you can create new instance of the Thread object in the start method:

def start(self):
    web_dir = os.path.join(os.path.dirname(__file__), 'www')
    os.chdir(web_dir)
    self.server_thread = threading.Thread(target=self.server.serve_forever, name="Server_Thread")
    self.server_thread.start()

In addition you also may clean the reference to the thread in stop method:

self.server_thread = None

RuntimeError: threads can only be started once Python Tkinter webserver

1 Answers