linux socket的select函数例子

用select函数可以以非阻塞的方式和多个socket通信。程序只是演示select函数的使用，功能非常简单，即使某个连接关闭以后也不会修改当前连接数，连接数达到最大值后会终止程序。

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);

}