Add a chapter on optimising communication (multiflight, packet queing)

Summary: related to T12804

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen, iljazovic

Differential Revision: https://repo.mireo.local/D28440

example/multiflight_client.cpp

@@ -0,0 +1,40 @@
+//[multiflight_client
+#include <iostream>
+
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/detached.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/signal_set.hpp>
+
+#include <async_mqtt5.hpp>
+
+int main() {
+	boost::asio::io_context ioc;
+
+	async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket> client(ioc);
+
+	client.brokers("<your-mqtt-broker>", 1883)
+		.async_run(boost::asio::detached);
+
+	// Publish with QoS 2 five times in a row without waiting for the handler
+	// of the previous async_publish call to be invoked.
+	for (auto i = 1; i <= 5; ++i)
+		client.async_publish<async_mqtt5::qos_e::exactly_once>(
+			"<topic>", "Hello world!",
+			async_mqtt5::retain_e::no, async_mqtt5::publish_props {},
+			[i](async_mqtt5::error_code ec, async_mqtt5::reason_code rc, async_mqtt5::pubcomp_props) {
+				std::cout << "Publish number " << i << " completed with: " << std::endl;
+				std::cout << "\t ec: " << ec.message() << std::endl;
+				std::cout << "\t rc: " << rc.message() << std::endl;
+			}
+		);
+
+	// We can stop the Client by using signals.
+	boost::asio::signal_set signals(ioc, SIGINT, SIGTERM);
+	signals.async_wait([&client](async_mqtt5::error_code, int) {
+		client.async_disconnect(boost::asio::detached);
+	});
+
+	ioc.run();
+}
+//]