void accept_thread() {
       ip::tcp::acceptor acceptor(service,

                                  ip::tcp::endpoint(ip::tcp::v4(),

   8001));
       while ( true) {

           client_ptr new_( new talk_to_client);
           acceptor.accept(new_->sock());
           boost::recursive_mutex::scoped_lock lk(cs);
           clients.push_back(new_);

} }

   void handle_clients_thread() {
       while ( true) {

           boost::this_thread::sleep( millisec(1));
           boost::recursive_mutex::scoped_lock lk(cs);
           for(array::iterator b = clients.begin(),e = clients.end(); b

!= e; ++b)

               (*b)->answer_to_client();
           // 删除已经超时的客户端
           clients.erase(std::remove_if(clients.begin(), clients.end(),

                      boost::bind(&talk_to_client::timed_out,_1)),

   clients.end());
       }

   }
   int main(int argc, char* argv[]) {

       boost::thread_group threads;
       threads.create_thread(accept_thread);
       threads.create_thread(handle_clients_thread);
       threads.join_all();

}