如何制作paho-mqtt循环超时？

Question

使用Python Paho-MQTT，我试图从一个主题中获得1个消息，然后退出。如果在5秒内未收到消息，那么我想超时并退出。我遇到的问题是，即使发消息会更早收到，该代码也总是等待5秒。如果我删除了

sleep()

线，则根本不会收到任何消息。

import paho.mqtt.client as mqtt
import logging
import time

def on_message(client, userdata, message):
    logging.info(f"Received message: {message.payload}")
    client.loop_stop()

logging.basicConfig(level=logging.DEBUG, format="%(asctime)s [%(levelname)s] %(message)s")

mqttc = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
mqttc.enable_logger()
mqttc.on_message = on_message

mqttc.connect("mqtt.eclipseprojects.io")
mqttc.subscribe("#")
mqttc.loop_start()

time.sleep(5)

logging.info('Complete!')

输出：

2025-01-28 01:39:33,511 [DEBUG] Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b''
2025-01-28 01:39:33,511 [DEBUG] Sending SUBSCRIBE (d0, m1) [(b'#', 0)]
2025-01-28 01:39:33,632 [DEBUG] Received CONNACK (0, 0)
2025-01-28 01:39:33,634 [DEBUG] Received SUBACK
2025-01-28 01:39:33,634 [DEBUG] Received PUBLISH (d0, q0, r1, m0), 'AhoyDTU0600-Streusser/version', ...  (6 bytes)
2025-01-28 01:39:33,634 [INFO] Received message: b'0.8.83'
2025-01-28 01:39:38,517 [INFO] Complete!

Answer 1

在您的代码中，即使您在新线程中与

loop_start()

关闭连接

loop_stop()

，您的主线程仍将执行

time.sleep(5)

.

。

可能的解决方案是添加一个线程事件，该事件将在收到消息

并在5秒后等待事件或超时之后设置。

import paho.mqtt.client as mqtt
import logging
import threading

# Create an event to signal when a message is received
message_received_event = threading.Event()

def on_message(client, userdata, message):
    logging.info(f"Received message: {message.payload}")

    # Signal that a message has been received
    message_received_event.set()

    client.loop_stop()

logging.basicConfig(level=logging.DEBUG, format="%(asctime)s [%(levelname)s] %(message)s")

mqttc = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
mqttc.enable_logger()
mqttc.on_message = on_message

mqttc.connect("mqtt.eclipseprojects.io")
mqttc.subscribe("#")
mqttc.loop_start()

# Wait for a message or timeout after 5 seconds
message_received_event.wait(timeout=5)

logging.info('Complete!')