CODEWITHSUNDEEP
pythonmqttpaho
Maxinger15
Maxinger15

Reputation: 33

Publish in on_message with Paho Mqtt Client not working

The publish call in the main method dosen't send a message to the broker, but returns (0,2). on_publish won't be called. I am not sure how I should look where the error is. I tried qos=2 and run the main method async but it didn't fixed it. The base connection work, because the on_message is called. The mqtt-server works fine with other projects too. Has anyone some ideas?

import paho.mqtt.client as mqtt
import subprocess
import shutil
import os
import glob
import logging
from datetime import datetime
import RPi.GPIO as GPIO
import time
from multiprocessing import Pool
GPIO.setmode(GPIO.BCM)

direction = 19
pwm = 26
GPIO.setup(direction, GPIO.OUT)
GPIO.setup(pwm, GPIO.OUT)

pwm = GPIO.PWM(pwm,19000)
speed = 0
pwm.start(speed)
running = False

client = mqtt.Client()
#First: pip3 install paho-mqtt
print("Starte Listener")

def start():
    GPIO.output(direction, GPIO.LOW)
    for dc in range(10, 40, 1):
        speed = dc 
        pwm.ChangeDutyCycle(speed)
        time.sleep(0.25)

def end():
    GPIO.output(direction, GPIO.LOW)
    for dc in list(reversed(range(0,40,1))):
        speed = dc 
        pwm.ChangeDutyCycle(speed)
        time.sleep(0.5)


def main(mqttClient):
    print("Started Spinning")
    running = True
    start()
    print(mqttClient.publish("scanner","shoot"))
    print("Waiting 124 seconds")
    time.sleep(124)
    print("ending spinning")
    end()
    print("finished spinning")
    running = False 

def on_connect2(client, userdata, flags, rc):
    client.subscribe("scanner",2)
    print("Connected "+str(rc))
    

# The callback for when a PUBLISH message is received from the server.
def on_message(mqttClient, userdata, msg):
    print("Recived message: "+str(msg.payload,'UTF-8'))
    if(str(msg.payload,'UTF-8') == "spin" and running == False):
        main(mqttClient)

def disconnected():
    print("Disconneted")

def on_publish(self, client, userdata, mid):
    print("onPublish")
    print(client,userdata,mid)

logger = logging.getLogger(__name__)
client.enable_logger(logger)

client.on_connect = on_connect2
client.on_message = on_message
client.on_publish = on_publish
client.on_disconnect = disconnected
client.username_pw_set("....","....")
client.connect("gx1", 1883,60)
client.loop_forever()

Upvotes: 1

Views: 4138

Answers (2)

hardillb
hardillb

Reputation: 59608

This is because you are blocking the MQTT client thread.

When you call client.loop_forever() it takes over the processes main thread and uses it to handle all the MQTT communication. When a new message is received it is picked up from the network stack by the MQTT client thread and turned into the message object that is then passed to the on_message() callback. This function runs on the client thread.

When you call client.publish() this will do one of 2 things

  1. If the message is QOS 0 and smaller than the network MTU it will publish the message.
  2. If the message is QOS 1 or 2 or larger than the network MTU then it will queue the message to be handled by the client thread.

The problem* in your code is that you are blocking the return from main() by 124 seconds which in turn is blocking the return of the on_message() function so the client thread can not get to publishing your message.

If you want to do things the take a long time or block in the on_message() (or any of the callback functions) you should start a separate thread to run them on.

*In theory your message looks like it should fall into case 1 listed above, but there may be other factors that are causing it to queue)

Upvotes: 1

Maxinger15
Maxinger15

Reputation: 33

As a quickfix I created a new Client:

def main(mqttClient):
    print("Started Spinning")
    running = True
    start()
    mq = mqtt.Client("shot_idicator")
    mq.username_pw_set("...","...")
    mq.connect("gx1", 1883,60)
    mq.publish("scanner","shoot")
    mq.disconnect()
    mq = None
    print("Waiting 124 seconds")
    time.sleep(124)
    print("ending spinning")
    end()
    print("finished spinning")
    running = False

Now it works but I think this is not how it should be done.

Upvotes: 0

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