Improved transport examples

example/transport_eh.cpp

@@ -0,0 +1,90 @@
+//Copyright (c) 2018 Emil Dotchevski
+//Copyright (c) 2018 Second Spectrum, Inc.
+
+//Distributed under the Boost Software License, Version 1.0. (See accompanying
+//file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+//This is a simple program that demonstrates the use of LEAF to transport error info between threads,
+//without using exception handling. See transport_eh.cpp for the (simpler) exception-handling variant.
+
+#include <boost/leaf/transport.hpp>
+#include <boost/leaf/expect.hpp>
+#include <boost/leaf/put.hpp>
+#include <string>
+#include <future>
+#include <vector>
+#include <algorithm>
+#include <iterator>
+#include <iostream>
+
+namespace leaf = boost::leaf;
+
+//Define several error info types.
+struct failed_thread_id { std::thread::id value; };
+struct failure_info1 { std::string value; };
+struct failure_info2 { int value; };
+
+//A type that represents a successfully generated value from a task.
+struct task_result { };
+
+//An exception type thrown in case of task failure.
+struct failure : virtual std::exception { };
+
+//This is a test task which succeeds or fails depending on its argument. In case of success, it returns
+//task_result, in case of error it throws failure.
+task_result
+task( bool succeed )
+	{
+	auto put = leaf::preload( failed_thread_id{std::this_thread::get_id()} ); //Report this thread's id (if expected).
+
+	if( succeed )
+		return task_result { };
+	else
+		leaf::throw_with_info( failure(), failure_info1{"info"}, failure_info2{42} ); //Also report both failure_info1 and failure_info2 (if expected).
+	}
+
+//Launch the specified number of asynchronous tasks. In case an asynchronous task throws, its error info
+//(of the types used to instantiate leaf::transport) will be automatically captured and transported to the
+//main thread.
+std::vector<std::future<task_result>>
+launch_async_tasks( int thread_count )
+	{
+	std::vector<std::future<task_result>> fut;
+	std::generate_n( std::inserter(fut,fut.end()), thread_count, [ ]
+		{
+		return std::async( std::launch::async,
+			leaf::transport<failed_thread_id,failure_info1,failure_info2>( [ ] { return task(rand()%4); } ) );
+		} );
+	return fut;
+	}
+
+int
+main()
+	{
+	//Launch asynchronous tasks.
+	auto fut = launch_async_tasks(42);
+
+	//Collect results or deal with failures.
+	for( auto & f : fut )
+		{
+		f.wait();
+		try
+			{
+			//Get the result, or setup any exception info from the task thread into this thread.
+			task_result r = leaf::get(f);
+
+			//No exception, consume the result.
+			std::cout << "Success!" << std::endl;
+			}
+		catch( failure const & )
+			{
+			//Caught exception from the task. Inspect and print the info.
+			leaf::available info;
+
+			unwrap( info.match<failure_info1,failure_info2,failed_thread_id>( [ ] ( std::string const & v1, int v2, std::thread::id tid )
+				{
+				std::cerr << "Error in thread " << tid << "! failure_info1: " << v1 << ", failure_info2: " << v2 << std::endl;
+				} ) );
+			}
+		}
+	}