工作代码片段-epoll

测试的实例：

        int fd =  open("a.txt", 'r');
        epoll_event ev;
        int efd = epoll_create(1);
        ev.events = EPOLLIN | EPOLLOUT;
        ev.data.fd = fd;
        epoll_ctl(efd, EPOLL_CTL_ADD, fd, &ev);
        epoll_event evs[3];
        int r = epoll_wait(efd, evs, 1, 0);
        if(r == -1) {
            std::cout << "error" << std::endl;
        }
        for(int i =0; i < 1; ++i) {
            std::cout << " >>>"<< evs[i].data.fd << std::endl;
            std::cout << "===" << evs[i].events << std::endl;
            char buff[300];
            read(fd, buff, 12);
            std::cout << buff<< std::endl;
        }
        epoll_ctl(efd, EPOLL_CTL_MOD, fd, &ev);

       int m = epoll_wait(efd, evs, 1, 0);
       if(m == -1) {
             std::cout << "error" << std::endl;
        }
       for(int i =0; i < 1; ++i) {
           std::cout << " >>>"<< evs[i].data.fd << std::endl;
           std::cout << "===" << evs[i].events << std::endl;
       }
       close(sfd);