摘要：
pg=65.Errorhandling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。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#include#include#include#include#includeboost::mutexglobal_stream_lock;voidWorkerThread{global_stream_lock.lock();std::cout˂˂"["˂˂boost::this_thread::get_id()˂˂"]ThreadStart"˂run();}catch{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()˂˂"]ThreadFinish"˂˂std::endl;global_stream_lock.unlock();}voidRaiseAnException{global_stream_lock.lock();std::cout˂˂"["˂˂boost::this_thread::get_id()˂˂"]"˂˂__FUNCTION__˂post;throw(std::runtime_error("Oops!"));}intmain{boost::shared_ptrio_service;boost::shared_ptrwork;global_stream_lock.lock();std::cout˂˂"["˂˂boost::this_thread::get_id()˂˂"]Theprogramwillexitwhenallworkhasfinished."˂post;worker_threads.join_all();return0;}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。
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;
}