selcect并发理解
假设backlog=10，selcet的并发是指什么呢？
同时有10个用户请求连接，selcet之后，对有数据的描述符进行统一的循环处理，不也会出现read write阻塞主循环的情形么？还是在一个个处理啊。如果没有selcet，也是在排队等待处理呀？
在accept之后得到新的fd，这个fd会一直保留么？还是超时了就把他清除掉了呢？
并发不应该是多线程来解决的事么
达人帮忙解惑啊，多谢了
while (1) { // initialize file descriptor set FD_ZERO(&fdsr); FD_SET(sock_fd, &fdsr); // timeout setting tv.tv_sec = 30; tv.tv_usec = 0; // add active connection to fd set for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { FD_SET(fd_A[i], &fdsr); } } ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv); if (ret < 0) { perror("select"); break; } else if (ret == 0) { printf("timeout\n"); continue; } // check every fd in the set for (i = 0; i < conn_amount; i++) { if (FD_ISSET(fd_A[i], &fdsr)) { ret = recv(fd_A[i], buf, sizeof(buf), 0); if (ret <= 0) { // client close printf("client[%d] close\n", i); close(fd_A[i]); FD_CLR(fd_A[i], &fdsr); fd_A[i] = 0; } else { // receive data if (ret < BUF_SIZE) memset(&buf[ret], '\0', 1); printf("client[%d] send:%s\n", i, buf); } } } // check whether a new connection comes if (FD_ISSET(sock_fd, &fdsr)) { new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size); if (new_fd <= 0) { perror("accept"); continue; } // add to fd queue if (conn_amount < BACKLOG) { fd_A[conn_amount++] = new_fd; printf("new connection client[%d] %s:%d\n", conn_amount, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port)); if (new_fd > maxsock) maxsock = new_fd; } else { printf("max connections arrive, exit\n"); send(new_fd, "bye", 4, 0); close(new_fd); break; } } showclient(); } // close other connections for (i = 0; i < BACKLOG; i++) { if (fd_A[i] != 0) { close(fd_A[i]); } } exit(0);}