树莓派systemd单元Python脚本time.sleep超60秒失效求助

在树莓派上运行一个由systemd管理的Python脚本，实现通电自动发送温湿度数据。当time.sleep(60)时一切正常，但设置为120秒及更长时间后，仅脚本启动时发送一次数据，后续不再发送任何数据。

代码示例 #

import paho.mqtt.client as mqtt
import Adafruit_DHT
import time
import ssl

# 配置DHT22传感器
dht_sensor = Adafruit_DHT.DHT22
dht_pin = 4  # 传感器连接的GPIO引脚号

username = 'master:mqttuser'
secret = 'ifYrtDSc'
host = '192.168.0.65'
port = 8883
clientID = 'raspi_ka'
assetID = '3nRdfjgE0Ga'


def on_connect(client, userdata, flags, rc):
    print("连接成功，返回码: " + str(rc))

    # 在on_connect中订阅，断开重连后会自动重新订阅
    mqtt_client.subscribe("$SYS/#")


def on_publish(client, userdata, msg):
    print(msg.topic + " " + str(msg.payload))


mqtt_client = mqtt.Client(clientID)
mqtt_client.username_pw_set(username, password=secret)
context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
mqtt_client.tls_set_context(context)
mqtt_client.on_connect = on_connect
mqtt_client.on_publish = on_publish
mqtt_client.connect(host, port=port)

# 循环读取并发送温湿度数据
while True:
    humidity, temperature = Adafruit_DHT.read_retry(dht_sensor, dht_pin)
    if humidity is not None and temperature is not None:
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/temperature/{assetID}", temperature)
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/humidity/{assetID}", humidity)
    else:
        print("读取传感器数据失败")
    time.sleep(120)

# 断开MQTT客户端连接
mqtt_client.disconnect()

问题根源是MQTT客户端未处理网络心跳。paho-mqtt客户端需要定期和Broker交换心跳包维持连接，当time.sleep时间过长时，客户端被阻塞，无法响应Broker的ping请求，导致Broker判定连接断开，后续publish操作自然失效。

方案1：启动后台loop线程处理网络通信 #

这是最可靠的解决方式，让客户端在后台持续处理心跳、重连等网络操作，不受time.sleep阻塞影响。修改代码如下：

import paho.mqtt.client as mqtt
import Adafruit_DHT
import time
import ssl

# 配置DHT22传感器
dht_sensor = Adafruit_DHT.DHT22
dht_pin = 4  # 传感器连接的GPIO引脚号

username = 'master:mqttuser'
secret = 'ifYrtDSc'
host = '192.168.0.65'
port = 8883
clientID = 'raspi_ka'
assetID = '3nRdfjgE0Ga'


def on_connect(client, userdata, flags, rc):
    print("连接成功，返回码: " + str(rc))
    mqtt_client.subscribe("$SYS/#")


def on_publish(client, userdata, msg):
    print(msg.topic + " " + str(msg.payload))


def on_disconnect(client, userdata, rc):
    if rc != 0:
        print(f"意外断开连接，返回码: {rc}")
        # 自动尝试重连
        client.reconnect()


mqtt_client = mqtt.Client(clientID)
mqtt_client.username_pw_set(username, password=secret)
context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
mqtt_client.tls_set_context(context)
mqtt_client.on_connect = on_connect
mqtt_client.on_publish = on_publish
mqtt_client.on_disconnect = on_disconnect  # 添加断开回调
mqtt_client.connect(host, port=port)

# 启动后台线程处理MQTT网络循环
mqtt_client.loop_start()

while True:
    humidity, temperature = Adafruit_DHT.read_retry(dht_sensor, dht_pin)
    if humidity is not None and temperature is not None:
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/temperature/{assetID}", temperature)
        mqtt_client.publish(f"master/{clientID}/writeattributevalue/humidity/{assetID}", humidity)
    else:
        print("读取传感器数据失败")
    time.sleep(120)

# 程序结束时停止loop线程并断开连接（实际循环不会走到这里）
mqtt_client.loop_stop()
mqtt_client.disconnect()

• loop_start()启动后台线程，持续处理MQTT协议的网络交互，包括心跳包、重连逻辑。
• 添加on_disconnect回调，能监控连接状态，连接异常时自动尝试重连。

方案2：调整心跳超时时间（备选） #

如果不想修改线程逻辑，可以延长Broker的连接超时时间，让它等待更久才判定连接断开：
在connect方法中添加keepalive参数：

# 设置keepalive为300秒（Broker会在1.5倍该时间后断开，即450秒）
mqtt_client.connect(host, port=port, keepalive=300)

这种方法只能缓解问题，无法彻底解决网络波动导致的连接断开，不如方案1可靠。

内容的提问来源于stack exchange，提问作者deputy-chief-hardy