IO多路复用之select全面总结(必看篇)

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include <netinet/in.h>

#include <sys/socket.h>

#include <sys/select.h>

#include <sys/types.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <assert.h>

#define IPADDR   "127.0.0.1"

#define PORT    8787

#define MAXLINE   1024

#define LISTENQ   5

#define SIZE    10

typedef struct server_context_st

{

  int cli_cnt;    /*客户端个数*/

  int clifds[SIZE];  /*客户端的个数*/

  fd_set allfds;   /*句柄集合*/

  int maxfd;     /*句柄最大值*/

} server_context_st;

static server_context_st *s_srv_ctx = NULL;

/*===========================================================================

 * ==========================================================================*/

static int create_server_proc(const char* ip,int port)

{

  int fd;

  struct sockaddr_in servaddr;

  fd = socket(AF_INET, SOCK_STREAM,0);

  if (fd == -1) {

    fprintf(stderr, "create socket fail,erron:%d,reason:%s\n",

        errno, strerror(errno));

    return -1;

  }

  /*一个端口释放后会等待两分钟之后才能再被使用，SO_REUSEADDR是让端口释放后立即就可以被再次使用。*/

  int reuse = 1;

  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) == -1) {

    return -1;

  }

  bzero(&servaddr,sizeof(servaddr));

  servaddr.sin_family = AF_INET;

  inet_pton(AF_INET,ip,&servaddr.sin_addr);

  servaddr.sin_port = htons(port);

  if (bind(fd,(struct sockaddr*)&servaddr,sizeof(servaddr)) == -1) {

    perror("bind error: ");

    return -1;

  }

  listen(fd,LISTENQ);

  return fd;

}

static int accept_client_proc(int srvfd)

{

  struct sockaddr_in cliaddr;

  socklen_t cliaddrlen;

  cliaddrlen = sizeof(cliaddr);

  int clifd = -1;

  printf("accpet clint proc is called.\n");

ACCEPT:

  clifd = accept(srvfd,(struct sockaddr*)&cliaddr,&cliaddrlen);

  if (clifd == -1) {

    if (errno == EINTR) {

      goto ACCEPT;

    } else {

      fprintf(stderr, "accept fail,error:%s\n", strerror(errno));

      return -1;

    }

  }

  fprintf(stdout, "accept a new client: %s:%d\n",

      inet_ntoa(cliaddr.sin_addr),cliaddr.sin_port);

  //将新的连接描述符添加到数组中

  int i = 0;

  for (i = 0; i <SIZE; i++) {

    if (s_srv_ctx->clifds[i] <0) {

      s_srv_ctx->clifds[i] = clifd;

      s_srv_ctx->cli_cnt++;

      break;

    }

  }

  if (i == SIZE) {

    fprintf(stderr,"too many clients.\n");

    return -1;

  }

101 }

static int handle_client_msg(int fd, char *buf)

{

  assert(buf);

  printf("recv buf is :%s\n", buf);

  write(fd, buf, strlen(buf) +1);

  return 0;

}

static void recv_client_msg(fd_set *readfds)

{

  int i = 0, n = 0;

  int clifd;

  char buf[MAXLINE] = {0};

  for (i = 0;i <= s_srv_ctx->cli_cnt;i++) {

    clifd = s_srv_ctx->clifds[i];

    if (clifd <0) {

      continue;

    }

    /*判断客户端套接字是否有数据*/

    if (FD_ISSET(clifd, readfds)) {

      //接收客户端发送的信息

      n= read(clifd, buf, MAXLINE);

      if (n <= 0) {

        /*n==0表示读取完成，客户都关闭套接字*/

        FD_CLR(clifd, &s_srv_ctx->allfds);

        close(clifd);

        s_srv_ctx->clifds[i] = -1;

        continue;

      }

      handle_client_msg(clifd, buf);

    }

  }

}

static void handle_client_proc(int srvfd)

{

  int clifd = -1;

  int retval = 0;

  fd_set *readfds = &s_srv_ctx->allfds;

  struct timeval tv;

  int i = 0;

  while (1) {

    /*每次调用select前都要重新设置文件描述符和时间，因为事件发生后，文件描述符和时间都被内核修改啦*/

    FD_ZERO(readfds);

    /*添加监听套接字*/

    FD_SET(srvfd, readfds);

    s_srv_ctx->maxfd = srvfd;

    tv.tv_sec = 30;

    tv.tv_usec = 0;

    /*添加客户端套接字*/

    for (i = 0; i <s_srv_ctx->cli_cnt; i++) {

      clifd = s_srv_ctx->clifds[i];

      /*去除无效的客户端句柄*/

      if (clifd != -1) {

        FD_SET(clifd, readfds);

      }

      s_srv_ctx->maxfd = (clifd > s_srv_ctx->maxfd ? clifd : s_srv_ctx->maxfd);

    }

    /*开始轮询接收处理服务端和客户端套接字*/

    retval = select(s_srv_ctx->maxfd + 1, readfds, NULL, NULL, &tv);

    if (retval == -1) {

      fprintf(stderr, "select error:%s.\n", strerror(errno));

      return;

    }

    if (retval == 0) {

      fprintf(stdout, "select is timeout.\n");

      continue;

    }

    if (FD_ISSET(srvfd, readfds)) {

      /*监听客户端请求*/

      accept_client_proc(srvfd);

    } else {

      /*接受处理客户端消息*/

      recv_client_msg(readfds);

    }

  }

}

static void server_uninit()

{

  if (s_srv_ctx) {

    free(s_srv_ctx);

    s_srv_ctx = NULL;

  }

}

static int server_init()

{

  s_srv_ctx = (server_context_st *)malloc(sizeof(server_context_st));

  if (s_srv_ctx == NULL) {

    return -1;

  }

  memset(s_srv_ctx, 0, sizeof(server_context_st));

  int i = 0;

  for (;i <SIZE; i++) {

    s_srv_ctx->clifds[i] = -1;

  }

  return 0;

}

int main(int argc,char *argv[])

{

  int srvfd;

  /*初始化服务端context*/

  if (server_init() < 0) {

    return -1;

  }

  /*创建服务,开始监听客户端请求*/

  srvfd = create_server_proc(IPADDR, PORT);

  if (srvfd < 0) {

    fprintf(stderr, "socket create or bind fail.\n");

    goto err;

  }

  /*开始接收并处理客户端请求*/

  handle_client_proc(srvfd);

  server_uninit();

  return 0;

err:

  server_uninit();

  return -1;

}