I/O多路复用模型之select（一）

#include<stdio.h>
 
#include<stdlib.h>
 
#include<unistd.h>
 
#include<errno.h>
 
#include<netdb.h>
 
#include<sys/types.h>
 
#include<sys/socket.h>
 
#include<netinet/in.h>
 
#include<arpa/inet.h>
 
#include<netdb.h>
 
#include<sys/time.h>
 
#include<string.h>
 
#include<sys/select.h>
 
#include<pthread.h>
 
 
 
 
/*************************
*用于返回最大文件描述值
*
*************************/
int max_fd(int a[], int num)
{
    int max = -1;
    int i = 0;
    for(i = 0; i < num; i++)
    {
        if(a[i] > max)
        {
            max = a[i];
 
        }
    }
 
    return max;
}
 
int main(int argc, char *argv[])
{
    int sockfd = 0;
    int confd = 0;
    int i = 0, j = 0;
    fd_set fd_read[2];
    int clifd[FD_SETSIZE]; /*存放监听以及已与客户连接的套接字*/
    int fd_count = 0; /*已经连接的套接字个数*/
    struct sockaddr_in seradd, cliadd;
    int fd_ret = 0;
    socklen_t cli_len = sizeof(cliadd);
    char readbuf[1024];
    char writebuf[1024];
    /*create sock;*/
    sockfd = socket(AF_INET, SOCK_STREAM, 0); /*此套接字是阻塞的*/
    if(sockfd < 0)
    {
        perror("sock create fail !!");
        exit(-1);
    }
 
 
    seradd.sin_family = AF_INET;
    seradd.sin_port = htons(8080);
    seradd.sin_addr.s_addr = htonl(INADDR_ANY);
 
    /*bind*/
    if(-1 == (bind(sockfd, (struct sockaddr *)&seradd, sizeof(struct sockaddr))))
    {
        perror("bind error");
        exit(-1);
    }
 
    /*listen*/
    if(-1 == (listen(sockfd, 5)))
    {
        perror("listen error");
        exit(-1);
    }
 
    //memset(&fd_read[0],0,sizeof(fd_read[0]));
 
    FD_ZERO(&fd_read[0]); /*清空fd_read[0]所有位*/
    FD_SET(sockfd, &fd_read[0]); /*将sockfd添加到fd_read[0]描述集中，也就是说将sockfd对应的fd_read[0]位中置位*/
    for(i = 0; i < FD_SETSIZE; i++)
    {
        clifd[i] = -1;
    }
 
    clifd[0] = sockfd;
    printf("--ser start work---\n");
    while(1)
    {
        FD_ZERO(&fd_read[1]);
        fd_read[1] = fd_read[0]; /*每次select后，没有达到条件的描述将被清空，所以每次都需要重新赋值*/
        /*进程将阻塞在select函数处，直到在整个队列中有读描述符可用为止，个人理解--内核检测整个队列，然后将可用的描述符返回（一个或多个，一个没有时将阻塞）*/
        fd_ret = select(max_fd(clifd, FD_SETSIZE) + 1, &fd_read[1], NULL, NULL, NULL); /*我们只关心读描述符集*/
 
        if(fd_ret < 0)
        {
            perror("select error");
        }
        else if(fd_ret > 0)
        {
            /*是监听套接字可读*/
            if(FD_ISSET(sockfd, &fd_read[1]) && (fd_count < FD_SETSIZE - 1))
            {
 
                confd = accept(sockfd, (struct sockaddr *)&cliadd, &cli_len); /*获取与客户端连接套接字*/
                if(-1 == confd)
                {
                    perror("confd error");
                }
 
                for(i = 1; i < FD_SETSIZE; i++)
                {
                    if(clifd[i] == -1)
                    {
                        clifd[i] = confd; /*将获得新连接套接字放到clifd数组中*/
                        FD_SET(confd, &fd_read[0]); /*将获得新连接套接字添加到读描述集中*/
                        fd_count++;
                        break;
                    }
                }
            }
 
            /*连接套接字可读*/
            for(j = 1; j < FD_SETSIZE; j++)
            {
                if(FD_ISSET(clifd[j], &fd_read[1]))
                {
                    /*从clifd[i]套接字中读取数据*/
                    if(read(clifd[j], readbuf, sizeof(readbuf)) <= 0)
                    {
                        perror("read data error");
                        FD_CLR(clifd[j], &fd_read[0]); /*将clifd[j]描述从读描述符集中删除*/
                        close(clifd[j]); /*关闭该套接字*/
                        clifd[j] = -1;
                        fd_count--;
                        continue;
 
                    }
 
                    strcpy(writebuf, readbuf);
                    printf("read data:%s\n", readbuf);
                    if(write(clifd[j], writebuf, sizeof(writebuf)) <= 0)
                    {
                        perror("write data error");
                        FD_CLR(clifd[j], &fd_read[0]);
                        close(clifd[j]);
                        clifd[j] = -1;
                        fd_count--;
                        continue;
                    }
                }
            }
        }
 
 
    }
 
}