选择c:wfds始终处于打开状态,导致阻塞

由于某种原因,FD_ISSET总是为&wfds,即使没有什么可发送的。这是代码片段(在客户端和服务器上都相同)。客户端和服务器都遇到了相同的问题,select表示wfds已打开。难道它不应该只在我在键盘上键入消息并按enter键时激活吗?

while (1) {
            //trying select..
            tv.tv_sec = 29;
            tv.tv_usec = 500000;
            FD_ZERO(&rfds);
            FD_ZERO(&wfds);
            FD_SET(new_sockfd, &rfds);
            FD_SET(new_sockfd, &wfds);

            n = select(new_sockfd + 1, &rfds, &wfds, NULL, &tv);

            if (n > 0) {
                if (FD_ISSET(new_sockfd, &rfds)) {

                    while (1) {
                        if ((num = recv(new_sockfd, buffer, 10240, 0)) == -1) {
                            //fprintf(stderr,"Error in receiving message!!\n");
                            perror("recv");
                            exit(1);
                        } else if (num == 0) {
                            printf("Connection closed\n");
                            return 0;
                        }
                        buffer[num] = '\0';
                        printf("Message received: %s\n", buffer);
                        break;
                    }
                }
                //this always returns true on client and host
                if (FD_ISSET(new_sockfd, &wfds)) {

                    while (1) {
                        fgets(buffer, MAXDATASIZE - 1, stdin);
                        if ((send(new_sockfd, buffer, strlen(buffer), 0)) == -1) {
                            fprintf(stderr, "Failure Sending Message\n");
                            close(new_sockfd);
                            exit(1);
                        } else {
                            printf("Message being sent: %s\n", buffer);
                            break;
                        }
                    }
                } 
            }
        }