boost中多线程下post与dispatch(转载)

  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。

#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.