python socketio和Flask:如何在后台线程中停止循环？

from flask import Flask, render_template
from flask_socketio import SocketIO, emit
import threading

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret'
socketio = SocketIO(app)

# 后台线程
thread = None
thread_stop_event = threading.Event()

def background_thread():
    count = 0
    while not thread_stop_event.is_set():
        count += 1
        socketio.emit('server_response', {'data': count}, namespace='/test')
        socketio.sleep(1)

@app.route('/')
def index():
    return render_template('index.html')

@socketio.on('connect', namespace='/test')
def test_connect():
    global thread
    if thread is None:
        thread = socketio.start_background_task(target=background_thread)
    emit('server_response', {'data': 'Connected'})

@socketio.on('disconnect', namespace='/test')
def test_disconnect():
    thread_stop_event.set()

if __name__ == '__main__':
    socketio.run(app)