just_the_call_proxy.h

template <class U> class CallProxy
{   
     U *_p;
     std::recursive_mutex &_mtx;
     mutable bool _own;
 
public:
     CallProxy(U *pp, std::mutex &mtx) : _p(pp), _mtx(mtx), _own(true)
     {   
     }   
     CallProxy(CallProxy const &other)
         : _p(other._p), _mtx(other._mtx), _own(true)
     {   
         other._own = false;
     }   
     ~CallProxy()
     {   
         if (_own)
         {   
             _mtx.unlock();                                                                                                    
         }   
     }   
 
     CallProxy &operator=(CallProxy const &) = delete;
 
     U *operator->()
     {   
         return _p; 
     }   
};