http://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-started-with-boostasio?pg=4
本章节为io_service添加任务，并且区分dispatch与post的区别.如果说io_service是asio库的大脑，那么post与dispatch就是asio库的手和脚。
先看看示例1
#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(); io_service->run(); global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] Thread Finish" << std::endl;
global_stream_lock.unlock();
} size_t fib( size_t n )
{
if ( n <= 1 )
{
return n;
}
boost::this_thread::sleep(
boost::posix_time::milliseconds( 1000 )
);
return fib( n - 1 ) + fib( n - 2);
} void CalculateFib( size_t n )
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] Now calculating fib( " << n << " ) " << std::endl;
global_stream_lock.unlock(); size_t f = fib( n ); global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] fib( " << n << " ) = " << f << std::endl;
global_stream_lock.unlock();
} 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( CalculateFib, 3 ) );
io_service->post( boost::bind( CalculateFib, 4 ) );
io_service->post( boost::bind( CalculateFib, 5 ) ); work.reset(); worker_threads.join_all(); return 0;
}
代码使用智能指针控制io_service，使用mutex控制各个进程间的输出互斥。work类维持io_service的生命周期, 然后使用post添加执行任务。
在此基础上我们再查看post与dispatch的区别：
post 优先将任务排进处理队列，然后返回，任务会在某个时机被完成。
dispatch会即时请求io_service去调用指定的任务。
示例2
#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(); io_service->run(); global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] Thread Finish" << std::endl;
global_stream_lock.unlock();
} void Dispatch( int x )
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id() << "] "
<< __FUNCTION__ << " x = " << x << std::endl;
global_stream_lock.unlock();
} void Post( int x )
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id() << "] "
<< __FUNCTION__ << " x = " << x << std::endl;
global_stream_lock.unlock();
} void Run3( boost::shared_ptr< boost::asio::io_service > io_service )
{
for( int x = 0; x < 3; ++x )
{
io_service->dispatch( boost::bind( &Dispatch, x * 2 ) );
io_service->post( boost::bind( &Post, x * 2 + 1 ) );
boost::this_thread::sleep( boost::posix_time::milliseconds( 1000 ) );
}
} 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 < 1; ++x )
{
worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
} io_service->post( boost::bind( &Run3, io_service ) ); work.reset(); worker_threads.join_all(); return 0;
}
我们可以看到结果是先显示dispatch的结果然后才显示post结果，与预想的是一致的.