提高:: io_service对象::后函数内绑定组成 [英] boost::bind composition inside io_service::post function

问题描述

考虑下面的类

 类task_counter
{
        上市：
                task_counter（短，提高:: ASIO :: io_service对象和放大器;）;
                〜task_counter（无效）;
      模板＆LT; typename的CompletionHandler＆GT;
        无效exec_task（CompletionHandler处理）
        {
                授予访问权限（）;
                io_.post（升压::绑定（安培; task_counter :: exec_and_decrease_counter＆LT; CompletionHandler＆gt;中这一点，处理程序））;
        }        模板＆LT; typename的CompletionHandler＆GT;
        无效exec_and_decrease_counter（CompletionHandler处理）
        {
                处理程序（）;
                decrease_counter（）;
        }    私人的：
           ....
}
 

方法exec_task通过这种方式另一类称为：

  tc_msg-＆GT; exec_task（的boost ::绑定（安培; message_receiver :: HANDLE_MSG，对此，味精））;
 

编译失败在bind.hpp指出无效使用作废前pression的
我搞清楚这个问题应该是io_post函数，其参数是两个不同的boost ::绑定对象的组成里面。但我无法通过现实问题深深地去了。

解决方案

而不是：

<$p$p><$c$c>io_.post(boost::bind(&task_counter::exec_and_decrease_counter<CompletionHandler>,这一点，处理程序））;

请尝试以下操作：

 的#include＆LT;升压/绑定/ protect.hpp＆GT;
// ...io_.post(boost::bind(&task_counter::exec_and_decrease_counter<boost::_bi::protected_bind_t<CompletionHandler> ＆gt;中此，提振::保护（处理）））;
 

Given the following class

class task_counter                                                                                                                                           
{                                                                                                                                                            
        public:                                                                                                                                                      
                task_counter(short, boost::asio::io_service&);                                                                                                       
                ~task_counter(void);                                                                                                                                 


      template<typename CompletionHandler>                                                                                                                 
        void exec_task(CompletionHandler handler)                                                                                                            
        {                                                                                                                                                    
                grant_access();                                                                                                                              
                io_.post(boost::bind(&task_counter::exec_and_decrease_counter<CompletionHandler>, this, handler));                                           
        }                                                                                                                                                    

        template<typename CompletionHandler>                                                                                                                 
        void exec_and_decrease_counter(CompletionHandler  handler)                                                                                           
        {                                                                                                                                                    
                handler();                                                                                                                                   
                decrease_counter();                                                                                                                          
        }                                                                                                                                                    

    private:
           ....
}

Method exec_task is called by another class in this way:

 tc_msg->exec_task(boost::bind(&message_receiver::handle_msg, this, msg)); 

Compilation fails stating "invalid use of void expression" in bind.hpp I'm figuring out that the problem should be inside the io_post function whose argument is a composition of two different boost::bind objects. But I was unable to go deeply through the real problem.

解决方案

Instead of:

io_.post(boost::bind(&task_counter::exec_and_decrease_counter<CompletionHandler>, this, handler));

Try the following:

#include <boost/bind/protect.hpp>
//...

io_.post(boost::bind(&task_counter::exec_and_decrease_counter<boost::_bi::protected_bind_t<CompletionHandler> >, this, boost::protect(handler)));

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