Stopping a dash server inside a thread does not work

Question

I'm trying to stop a dash server within a thread, but it doesn't work:

Here's a minor example of the issue :

import threading
import requests
from dash import Dash, html
from flask import Flask, request
import logging
import time

# Setup Logger
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(threadName)s, %(levelname)s] %(message)s",
    handlers=[
        logging.StreamHandler()
    ]
)

# Create Flask server and associate it with the Dash app
flask_app = Flask(__name__)
app = Dash(__name__, server=flask_app)

# Define a simple layout
app.layout = html.Div(children=[
    html.H1(children='Hello Dash'),
    html.P(children='This is a simple Dash app for testing.'),
    html.Button('Click Me', id='button')
])

# Define a shutdown route
@app.server.route('/shutdown', methods=['POST'])
def shutdown():
    shutdown_server = request.environ.get('werkzeug.server.shutdown')
    if shutdown_server is None:
        raise RuntimeError('Not running with the Werkzeug Server')
    shutdown_server()
    return 'Server shutting down...'

# Function to run the server
def run_server():
    logging.info("Starting Dash server")
    app.run_server(debug=True, use_reloader=False)

# Function to stop the server
def stop_server():
    logging.info("Sending shutdown request")
    try:
        requests.post('http://127.0.0.1:8050/shutdown')
    except requests.RequestException as e:
        logging.error(f"Error sending shutdown request: {e}")
    logging.info("Joining server thread")
    server_thread.join()

# Start the server in a new thread
server_thread = threading.Thread(target=run_server)
server_thread.start()

# Start the server, wait a few seconds, then stop it
time.sleep(5)
stop_server()
logging.info("Server stopped")

When I run this script, the program hangs at server_thread.join() and does not exit. Using kill pid is not practical for me because I am running my program within a GUI application. Killing the pid would destroy the gui as well.

Answer 1

How about starting flask_app as a separate process instead of a thread. And then kill this process using pid.

from dash import Dash, html
from flask import Flask, request
import logging
import time
from multiprocessing import Process, current_process
import os

# Setup Logger
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(threadName)s, %(levelname)s] %(message)s",
    handlers=[
        logging.StreamHandler()
    ]
)

# Create Flask server and associate it with the Dash app
flask_app = Flask(__name__)
app = Dash(__name__, server=flask_app)

# Define a simple layout
app.layout = html.Div(children=[
    html.H1(children='Hello Dash'),
    html.P(children='This is a simple Dash app for testing.'),
    html.Button('Click Me', id='button')
])


# Define a shutdown route
@app.server.route('/shutdown', methods=['POST'])
def shutdown():
    proc = current_process()


# Function to run the server
def run_server():
    logging.info("Starting Dash server")
    app.run_server(debug=True, use_reloader=False)


# Function to stop the server
def stop_server(pid):
    logging.info("Sending shutdown request")
    os.kill(pid, 9)
    # requests.post('http://127.0.0.1:8050/shutdown')
    

if __name__ == '__main__':    
    # Start the server in a new thread
    server_proc = Process(target=run_server, 
                            name='dash_server', 
                            daemon=True)

    server_proc.start()
    pid = server_proc.pid
    # Start the server, wait a few seconds, then stop it
    time.sleep(5)
    stop_server(pid)
    logging.info("Server stopped")
    time.sleep(30)

To kill process on Windows try replacing with this lines:

import signal
os.kill(pid, signal.CTRL_C_EVENT)
# or signal.CTRL_BREAK_EVENT