CODEWITHSUNDEEP
pythonmqttpaho
schumacherj
schumacherj

Reputation: 1324

Using Paho's message_callback_add() function, but no results

I am attempting to catch messages by topic by using the message_callback_add() function in this library. Below is my entire module that I am using to deal with my mqtt subscribe and publishing needs. I have been able to test that the publish works, but I can't seem to catch any incoming messages. There are no warnings/errors of any kind and the print("position") statements are working for 1 and 2 only.

import sys
import os
import time
import Things
import paho.mqtt.client as paho

global mqttclient;
global broker;
global port;

broker = "10.64.16.199";
port = 1883;

mypid = os.getpid()
client_uniq = "pubclient_"+str(mypid)
mqttclient = paho.Client(client_uniq, False) #nocleanstart
mqttclient.connect(broker, port, 60)
mqttclient.subscribe("Commands/#")

def Pump_callback(client, userdata, message):
    #print("Received message '" + str(message.payload) + "' on topic '"
    #    + message.topic + "' with QoS " + str(message.qos))
    print("position 3")
    Things.set_waterPumpSpeed(int(message.payload))

def Valve_callback(client, userdata, message):
    #print("Received message '" + str(message.payload) + "' on topic '"
    #    + message.topic + "' with QoS " + str(message.qos))
    print("position 4")
    Things.set_valvePosition(int(message.payload))

mqttclient.message_callback_add("Commands/PumpSpeed", Pump_callback)
mqttclient.message_callback_add("Commands/ValvePosition", Valve_callback)

print("position 1")
mqttclient.loop_start()
print("position 2")


def pub(topic, value):
  mqttclient.publish(topic, value, 0, True)

Upvotes: 4

Views: 10939

Answers (2)

schumacherj
schumacherj

Reputation: 1324

I called loop_start in the wrong place.

I moved the call to right after the connect statement and it now works.

Here is the snippet:

client_uniq = "pubclient_"+str(mypid)
mqttclient = paho.Client(client_uniq, False) #nocleanstart
mqttclient.connect(broker, port, 60)

mqttclient.loop_start()
mqttclient.subscribe("FM_WaterPump/Commands/#")

In the documentation on loop_start it alludes to calling loop_start() after or before connect though it should say immediately before or after to clarify.

Snippet of the documentation:

These functions implement a threaded interface to the network loop. Calling loop_start() once, before or after connect*(), runs a thread in the background to call loop() automatically. This frees up the main thread for other work that may be blocking. This call also handles reconnecting to the broker. Call loop_stop() to stop the background thread.

Upvotes: 3

ralight
ralight

Reputation: 11608

loop_start() will return immediately, so your program will quit before it gets chance to do anything.

You've also called subscribe() before message_callback_add() which doesn't make sense, although in this specific example it probably doesn't matter.

Upvotes: 1

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