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

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#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

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#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

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#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

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#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

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#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

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#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; }

　　此类mutex对象不可递归锁定。如果递归锁定将造成死锁。