boost asio 学习(二)了解boost::bind

2.了解boost::bind
使用boost::bind封装一个函数，考虑以下例子
示例2a

#include <iostream>
#include <boost/bind.hpp>
 
void F1()
{
    std::cout << __FUNCTION__ << std::endl;
}
 
int main( int argc, char * argv[] )
{
    boost::bind( &F1 );
    return 0;
}

运行代码无输出，这是因为我们创建一个函数触发对象，但是没有实际调用。我们需要使用()操作符调用函数.
示例2b

#include <iostream>
#include <boost/bind.hpp>
 
void F1()
{
    std::cout << __FUNCTION__ << std::endl;
}
 
int main( int argc, char * argv[] )
{
    boost::bind( &F1 )();
    return 0;
}

现在运行示例，将输出文本。下面示例介绍如何传输参数
示例2C

#include <iostream>
#include <boost/bind.hpp>
 
void F2( int i, float f )
{
    std::cout << "i: " << i << std::endl;
    std::cout << "f: " << f << std::endl;
}
 
int main( int argc, char * argv[] )
{
    boost::bind( &F2, 42, 3.14f )();
    return 0;
}

运行程序将输出预期的文本。

下个示例显示bind类成员函数
示例2d

#include <iostream>
#include <boost/bind.hpp>
 
class MyClass
{
public:
    void F3( int i, float f )
    {
        std::cout << "i: " << i << std::endl;
        std::cout << "f: " << f << std::endl;
    }
};
 
int main( int argc, char * argv[] )
{
    MyClass c;
    boost::bind( &MyClass::F3, &c, 42, 3.14f )();
    return 0;
}

我们必须传递类对象的地址以便调用。如果是在类内部调用，则调用this指针或者shared_from_this().
在多线程中，io_service作为全局对象。在实际应用中，这种做法是不推荐的。如果我们尝试应用bind io_service对象，则会发生错误，因为io_service不能被拷贝，所以我们需要使用
shred_ptr.
示例2e

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/bind.hpp>
#include <iostream>
 
void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service )
{
    std::cout << "Thread Start\n";
    io_service->run();
    std::cout << "Thread Finish\n";
}
 
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 )
        );
 
    std::cout << "Press [return] to exit." << std::endl;
 
    boost::thread_group worker_threads;
    for( int x = 0; x < 4; ++x )
    {
        worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
    }
 
    std::cin.get();
 
    io_service->stop();
 
    worker_threads.join_all();
 
    return 0;
}

异步程序中，需要确认全局和共享数据的同步访问。下列示例示范了mutex对象的使用方法。
示例2f

#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();
}
 
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() 
        << "] Press [return] to exit." << std::endl;
    global_stream_lock.unlock();
 
    boost::thread_group worker_threads;
    for( int x = 0; x < 4; ++x )
    {
        worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
    }
 
    std::cin.get();
 
    io_service->stop();
 
    worker_threads.join_all();
 
    return 0;
}