Examples rework

Summary:
related to T15261, T15262
- all examples are added to CI checks
	- as a result, CMakeLists.txt in example folder is reworked to build all examples instead of one
	- also removed chapter Building with CMake temporarily (it will be back)
- all examples accept runtime arguments (brokers, port, clientid) (default: hivemq public broker)
- implemented example suggestions by R.Perez, most notable:
	- all examples include mqtt headers they use (no more unified headers)
	- multithreaded examples use thread_pool instead of asio::io_context
- all examples use logger with log_level::info by default

Reviewers: ivica

Reviewed By: ivica

Subscribers: iljazovic, miljen

Differential Revision: https://repo.mireo.local/D32602

example/hello_world_in_multithreaded_env.cpp

@@ -7,89 +7,98 @@
 
 //[hello_world_in_multithreaded_env
 #include <iostream>
-#include <vector>
+#include <string>
 #include <thread>
+#include <vector>
 
+#include <boost/asio/bind_executor.hpp>
 #include <boost/asio/detached.hpp>
-#include <boost/asio/io_context.hpp>
-#include <boost/asio/post.hpp>
+#include <boost/asio/dispatch.hpp>
+#include <boost/asio/thread_pool.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/asio/ip/tcp.hpp>
 
-#include <async_mqtt5.hpp>
+#include <async_mqtt5/logger.hpp>
+#include <async_mqtt5/mqtt_client.hpp>
+#include <async_mqtt5/reason_codes.hpp>
+#include <async_mqtt5/types.hpp>
 
-int main() {
-	// Create a multithreaded environment where 4 threads
-	// will be calling ioc.run().
+struct config {
+	std::string brokers = "broker.hivemq.com";
+	uint16_t port = 1883;
+	std::string client_id = "async_mqtt5_tester";
+};
 
-	// Number of threads that will call io_context::run().
-	int thread_num = 4;
-	boost::asio::io_context ioc(4);
+int main(int argc, char** argv) {
+	config cfg;
 
-	// Create the remaining threads (aside of this one).
-	std::vector<std::thread> threads;
-	threads.reserve(thread_num - 1);
+	if (argc == 4) {
+		cfg.brokers = argv[1];
+		cfg.port = uint16_t(std::stoi(argv[2]));
+		cfg.client_id = argv[3];
+	}
+
+	// Create a thread pool with 4 threads.
+	boost::asio::thread_pool tp(4);
 	
-	// Create an explicit strand from io_context's executor.
+	// Create an explicit strand from thread_pool's executor.
 	// The strand guarantees a serialised handler execution regardless of the 
-	// number of threads running in the io_context.
-	boost::asio::strand strand = boost::asio::make_strand(ioc.get_executor());
+	// number of threads running in the thread_pool.
+	boost::asio::strand strand = boost::asio::make_strand(tp.get_executor());
 
 	// Create the Client with the explicit strand as the default associated executor.
-	async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket> client(strand);
+	async_mqtt5::mqtt_client<
+		boost::asio::ip::tcp::socket, std::monostate /* TlsContext */, async_mqtt5::logger
+	> client(strand, {} /* tls_context */, async_mqtt5::logger(async_mqtt5::log_level::info));
 
 	// Configure the client.
-	client.brokers("<your-mqtt-broker>", 1883);
+	client.brokers(cfg.brokers, cfg.port) // Broker that we want to connect to.
+		.credentials(cfg.client_id); // Set the Client Identifier. (optional)
 
 	// Start the Client.
 	// The async_run function call must be posted/dispatched to the strand.
-	boost::asio::post(
-		strand,
-		[&client, &strand] { 
-			// Considering that the default associated executor of all completion handlers is the strand,
-			// it is not necessary to explicitly bind it to async_run or other async_xxx's handlers.
-			client.async_run(boost::asio::detached);
-		}
+	boost::asio::dispatch(
+		boost::asio::bind_executor(
+			strand,
+			[&client, &strand, &cfg] { 
+				// Considering that the default associated executor of all completion handlers is the strand,
+				// it is not necessary to explicitly bind it to async_run or other async_xxx's handlers.
+				client.async_run(boost::asio::detached); // Start the Client.
+			}
+		)
 	);
 	
 	// The async_publish function call must be posted/dispatched to the strand.
 	// The associated executor of async_publish's completion handler must be the same strand.
-	boost::asio::post(
-		strand,
-		[&client, &strand] { 
-			assert(strand.running_in_this_thread());
+	boost::asio::dispatch(
+		boost::asio::bind_executor(
+			strand,
+			[&client, &strand, &cfg] { 
+				assert(strand.running_in_this_thread());
 
-			client.async_publish<async_mqtt5::qos_e::at_least_once>(
-				"<your-mqtt-topic>", "Hello world!", async_mqtt5::retain_e::no,
-				async_mqtt5::publish_props {},
-				// You may bind the strand to this handler, but it is not necessary
-				// as the strand is already the default associated handler.
-				// However, you must not bind it to any other executor!
-				[&client, &strand](
-					async_mqtt5::error_code ec, async_mqtt5::reason_code rc,
-					async_mqtt5::puback_props props
-				) {
-					assert(strand.running_in_this_thread());
+				client.async_publish<async_mqtt5::qos_e::at_least_once>(
+					"async-mqtt5/test", "Hello World!", async_mqtt5::retain_e::no,
+					async_mqtt5::publish_props {},
+					// You may bind the strand to this handler, but it is not necessary
+					// as the strand is already the default associated handler.
+					[&client, &strand](
+						async_mqtt5::error_code ec, async_mqtt5::reason_code rc,
+						async_mqtt5::puback_props props
+					) {
+						assert(strand.running_in_this_thread());
 
-					std::cout << ec.message() << std::endl;
-					std::cout << rc.message() << std::endl;
+						std::cout << ec.message() << std::endl;
+						std::cout << rc.message() << std::endl;
 
-					// Stop the Client. This will cause ioc.run() to return.
-					client.cancel();
-				}
-			);
-		}
+						// Stop the Client.
+						client.cancel();
+					}
+				);
+			}
+		)
 	);
 
-	// Call ioc.run() on the other threads.
-	for (int i = 0; i < thread_num - 1; ++i)
-		threads.emplace_back([&ioc] { ioc.run(); });
-
-	// Call ioc.run() on this thread.
-	ioc.run();
-
-	for (auto& t : threads)
-		if (t.joinable()) t.join();
+	tp.join();
 
 	return 0;
 }