Originally posted by **byew** January 9, 2023
**Describe the question**
I am trying to complete a python backend server so that it could send messages to the front webpage when I receive data from Kafka.
I found that when I use ```time.sleep(1)``` or don't use ```socketio.sleep(1)``` or use ```eventlet.monkey_patch()```+```socketio.sleep(1)``` , the backend cannot use socketio.emit to send messages to the frontend webpage.. But when I use ```socketio.sleep(1)``` or use ```eventlet.monkey_patch()``` or use ```eventlet.monkey_patch()```+```time.sleep(1)``` , the program runs fine.
I don't know why this happens, so I want to ask everyone what the reason is?
Below is my code：
```
import time
from flask import Flask, render_template
from flask_socketio import SocketIO
from flask_socketio import emit, send
from threading import Lock
import threading
from flask_cors import CORS
from kafka import KafkaConsumer
import json
#improt eventlet
#eventlet.monkey_patch()
app = Flask(__name__, template_folder='templates')
app.config['SECRET_KEY'] = 'secret!'
CORS(app, resources=r'/*')
socketio = SocketIO(app)
thread = None
thread_lock = Lock()
# print(socketio.async_mode)#### eventlet
@app.route('/')
def index():
print("hello world")
return render_template('index1.html', async_mode=socketio.async_mode)
@socketio.on('message')
def handle_message(message):
send(message)
def background_thread():
consumer = KafkaConsumer(
'test',
consumer_timeout_ms=1 * 1000
)
# while True:
for msg in consumer:
data = json.loads(msg.value.decode('utf8'))
print(data)
socketio.emit("test", data)
socketio.sleep(1)
print("kafka timeout")
@socketio.on('connect')
def test_connect():
print("socket io connect")
# background_thread()
global thread
with thread_lock:
if thread is None:
thread = socketio.start_background_task(target=background_thread)
@socketio.on('disconnect', namespace='/test')
def test_disconnect():
print('Client disconnected')
@socketio.on('my event')
def handle_my_custom_event(json):
print('received json: ' + str(json))
if __name__ == '__main__':
# socketio.run(app, debug=True)
socketio.run(app, debug=True, host='0.0.0.0',port=5555)
```
Discussed in https://github.com/miguelgrinberg/Flask-SocketIO/discussions/1927