boost asio 学习(五) 错误处理

http://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-started-with-boostasio?pg=6

5. Error handling

接下来我们需要注意的话题是错误处理。换句话说就是函数抛出异常时发生了什么

Boost::asio 给予用户两种选择来处理。错误通过handler传播，指出线程呼叫run或者poll系列函数的位置。用户可以能处理通过异常抛出的状态或者是接收返回的错误变量。更多关于BOOST的信息，可以参考boost 的错误与异常处理。

首先我们看看异常处理错误的方法

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service )
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	try
	{
		io_service->run();
	}
	catch( std::exception & ex )
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] Exception: " << ex.what() << std::endl;
		global_stream_lock.unlock();
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void RaiseAnException( boost::shared_ptr< boost::asio::io_service > io_service )
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] " << __FUNCTION__ << std::endl;
	global_stream_lock.unlock();

	io_service->post( boost::bind( &RaiseAnException, io_service ) );

	throw( std::runtime_error( "Oops!" ) );
}

int main( int argc, char * argv[] )
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work( *io_service )
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] The program will exit when all work has finished." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for( int x = 0; x < 2; ++x )
	{
		worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
	}

	io_service->post( boost::bind( &RaiseAnException, io_service ) );

	worker_threads.join_all();

	return 0;
}

这个例子里，因为异常通过run函数释放，work线程因此退出。所有线程退出后，程序由于join_all的返回而结束。

下面看看使用错误变量返回异常的例子

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service )
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	boost::system::error_code ec;
	io_service->run( ec );

	if( ec )
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] Exception: " << ec << std::endl;
		global_stream_lock.unlock();
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void RaiseAnException( boost::shared_ptr< boost::asio::io_service > io_service )
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] " << __FUNCTION__ << std::endl;
	global_stream_lock.unlock();

	io_service->post( boost::bind( &RaiseAnException, io_service ) );

	throw( std::runtime_error( "Oops!" ) );
}

int main( int argc, char * argv[] )
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work( *io_service )
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] The program will exit when all work has finished." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for( int x = 0; x < 2; ++x )
	{
		worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
	}

	io_service->post( boost::bind( &RaiseAnException, io_service ) );

	worker_threads.join_all();

	return 0;
}

上面这个代码将引起程序崩溃。通过调试，我们可以发现抛出的异常没有被处理

正确处理如下

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread(boost::shared_ptr< boost::asio::io_service > io_service)
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	while (true)
	{
		try
		{
			boost::system::error_code ec;
			io_service->run(ec);
			if (ec)
			{
				global_stream_lock.lock();
				std::cout << "[" << boost::this_thread::get_id()
					<< "] Error: " << ec << std::endl;
				global_stream_lock.unlock();
			}
			break;
		}
		catch (std::exception & ex)
		{
			global_stream_lock.lock();
			std::cout << "[" << boost::this_thread::get_id()
				<< "] Exception: " << ex.what() << std::endl;
			global_stream_lock.unlock();
		}
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void RaiseAnException(boost::shared_ptr< boost::asio::io_service > io_service)
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] " << __FUNCTION__ << std::endl;
	global_stream_lock.unlock();

	io_service->post(boost::bind(&RaiseAnException, io_service));
	throw(std::runtime_error("Oops!"));

}

int main(int argc, char * argv[])
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work(*io_service)
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] The program will exit when all work has finished." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for (int x = 0; x < 2; ++x)
	{
		worker_threads.create_thread(boost::bind(&WorkerThread, io_service));
	}

	io_service->post(boost::bind(&RaiseAnException, io_service));

	worker_threads.join_all();

	return 0;
}