wait_for_publish() never ends and is_publish return False

[kessero]

My simple script for test without any logic only get message and send message. Hangs my script on wait_for_publish() or if i set ex. wait_for_publish(1) after 1 seconds goes further but message is published on server but info.is_published() return False

I made some tests and if I turn off client.loop_forever() and only make publish_data_to_broker() then everything works

broker = config.mqtt_broker

def on_connect(client, userdata, flags, rc, properties):
    if rc == 0:
        print("connected to topics")
        client.subscribe(config.main_topic + config.bileterka + "/#")
        client.subscribe(config.main_topic + config.terminal + "/#")
    else:
        print("errror")


def publish_data_to_broker(topic, msg, retain):
    global ostatnia_wiadomosc
    """
    Publikuje dane do brokera
    :param: topic, msg, retain
    """
    print(topic + " " + msg)
    info = client.publish("test", msg, qos=2, retain=retain)
    info.wait_for_publish()
    print(info)

    if info.is_published():
        print("published OK")
        return True
    else:
        logging.info(f"Pub fail {topic} {msg}")
    return False


def on_message(client, userdata, msg):
    msgIn = msg.payload.decode("utf-8")
    try:
        if "numerrej" in msg.topic:
            print("----")
            publish_data_to_broker(msg.topic, "test", False)
    except Exception as e:
        logging.error(f"on message {e}")


if __name__ == "__main__":
    client.username_pw_set(username=config.mqtt_login, password=config.mqtt_passwd)
    client.on_connect = on_connect
    client.on_message = on_message
    try:
        client.connect(broker, config.mqtt_port, config.mqtt_keepalive)
    except:
        logging.info("ERROR: Connect error")
    client.loop_forever()

Why wait_for_publish not work and is_publish return False with loop_forever ?
Is it possible to use wait_for_publish with loop or should i use threads?
Ubuntu server 24.04.01LTS
Python 3.10.12
paho-mqtt 2.1.0
mosquitto server 2.0.20

[MattBrittan]

on_message is called from within the network loop, if your handler code blocks, then the network loop is blocked (so nothing will be sent/received). You are calling wait_for_publish, which will block until the message is published, but as this blocks the network loop the message will not be sent (so you have a deadlock).

I'd suggest moving the stuff that needs to be done when the publish is complete off to an on_publish() callback. The alternative would be to perform the operation in a seperate thread.