Pending messages not published when using threading

[Viatorus]

We have got a reproducible issue when publishing messages right before the end of a mosquitto connection.

Pending messages will not published after calling disconnect or loop_stop().

We are looking for a functionality to flush all messages before a connection is closed.

Check out the following example.
Only if you uncomment the thread sleep, all messages will be published.

Mosquitto v. 1.4.14

#include <mosquittopp.h>

#include <iostream>
#include <thread>

using namespace std::chrono_literals;

int main() {
	mosqpp::mosquittopp mqo("foobar");
	try {
		if (mosqpp::lib_init() != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not init");
		}
		if (mqo.connect("0.0.0.0") != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not connect to server");
		}
		if (mqo.loop_start() != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not start loop");
		}

		mqo.publish(nullptr, "hello");
		mqo.publish(nullptr, "world");
		mqo.publish(nullptr, "how");
		mqo.publish(nullptr, "are");
		mqo.publish(nullptr, "you");

		// Uncomment this for a "workaround"
		// std::this_thread::sleep_for(1s);

		if (mqo.disconnect() != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not disconnect from server");
		}
		if (mqo.loop_stop(false) != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not stop loop");
		}
		if (mosqpp::lib_cleanup() != MOSQ_ERR_SUCCESS) {
			throw std::runtime_error("could not cleanup");
		}

	} catch (std::exception &e) {
		std::cerr << e.what() << "\n";
	}
}

[karlp]

I was under the impression you had to call stop before disconnect?

[Viatorus]

@karlp Not necessary but, lets try it out...

I tried many ways of "closing the connection" without success. Overall this is an annoying issue. :(

Not publishing all messages

if (mqo.disconnect() != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not disconnect from server");
}
if (mqo.loop_stop(true) != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not stop loop");
}

if (mqo.disconnect() != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not disconnect from server");
}
if (mqo.loop_stop(false) != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not stop loop");
}

Endless hangs but publish all messages

if (mqo.loop_stop(false) != MOSQ_ERR_SUCCESS) { // Hangs here forever
	throw std::runtime_error("could not stop loop");
}
if (mqo.disconnect() != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not disconnect from server");
}

Endless hangs and not publishing all messages

if (mqo.loop_stop(true) != MOSQ_ERR_SUCCESS) { // Hangs here forever
	throw std::runtime_error("could not stop loop");
}
if (mqo.disconnect() != MOSQ_ERR_SUCCESS) {
	throw std::runtime_error("could not disconnect from server");
}