人体有多少癌细胞:linux socket的select函数例子

1. 程序使用了一个数组fd_A，通信开始后把需要通信的多个socket描述符都放入此数组。

2. 首先生成一个叫sock_fd的socket描述符，用于监听端口。

3. 将sock_fd和数组fd_A中不为0的描述符放入select将检查的集合fdsr。

4. 处理fdsr中可以接收数据的连接。如果是sock_fd，表明有新连接加入，将新加入连接的socket描述符放置到fd_A。

#include
#include
#include
#include
#include
#include
#include
#include
#include

#define MYPORT 1234    // the port users will be connecting to

#define BACKLOG 5     // how many pending connections queue will hold

#define BUF_SIZE 200

int fd_A[BACKLOG];    // accepted connection fd
int conn_amount;    // current connection amount

void showclient()
{
    int i;
     printf("client amount: %d\n", conn_amount);
    for (i = 0; i < BACKLOG; i++) {
         printf("[%d]:%d  ", i, fd_A[i]);
     }
     printf("\n\n");
}

int main(void)
{
    int sock_fd, new_fd;  // listen on sock_fd, new connection on new_fd
    struct sockaddr_in server_addr;    // server address information
    struct sockaddr_in client_addr; // connector's address information
     socklen_t sin_size;
    int yes = 1;
    char buf[BUF_SIZE];
    int ret;
    int i;

    if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
         perror("socket");
         exit(1);
     }

    if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
         perror("setsockopt");
         exit(1);
     }
    
     server_addr.sin_family = AF_INET;         // host byte order
     server_addr.sin_port = htons(MYPORT);     // short, network byte order
     server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
     memset(server_addr.sin_zero, '\0', sizeof(server_addr.sin_zero));

    if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
         perror("bind");
         exit(1);
     }

    if (listen(sock_fd, BACKLOG) == -1) {
         perror("listen");
         exit(1);
     }

     printf("listen port %d\n", MYPORT);

     fd_set fdsr;
    int maxsock;
    struct timeval tv;

     conn_amount = 0;
     sin_size = sizeof(client_addr);
     maxsock = sock_fd;
    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);
}