Linux Select

Linux Select

在Linux中，我们可以使用select函数实现I/O端口的复用，传递给 select函数的参数会告诉内核：

      •我们所关心的文件描述符
      •对每个描述符，我们所关心的状态。(我们是要想从一个文件描述符中读或者写，还是关注一个描述符中是否出现异常)
      •我们要等待多长时间。(我们可以等待无限长的时间，等待固定的一段时间，或者根本就不等待)
   从 select函数返回后，内核告诉我们一下信息：
      •对我们的要求已经做好准备的描述符的个数
      •对于三种条件哪些描述符已经做好准备.(读，写，异常)

select
——用于IO多路复用
（1）函数原型

＃include<sys/time.h>＃include<sys/types.h>＃include<unistd.h>int select(int n,fd_set * readfds,fd_set * writefds,fd_set * exceptfds,struct timeval * timeout);

（2）参数
        n：最大的文件描述词加1；
        readfds、writefds 和exceptfds：称为描述词组，是用来回传该描述词的读，写或例外的状况；
        timeout：用来设置select()的等待时间。

struct timeval{  time_t tv_sec;  time_t tv_usec;};

（3）返回值
        如果参数timeout设为NULL则表示select（）没有timeout。
执行成功则返回文件描述词状态已改变的个数，如果返回0代表在描述词状态改变前已超过timeout时间，当有错误发生时则返回-1，错误原因存于errno，此时参数readfds，writefds，exceptfds和timeout的值变成不可预测。
EBADF 文件描述词为无效的或该文件已关闭
EINTR 此调用被信号所中断
EINVAL 参数n 为负值。

ENOMEM 核心内存不足

常见的程序片段:fs_set readset；FD_ZERO(&readset);FD_SET(fd,&readset);select(fd+1,&readset,NULL,NULL,NULL);if(FD_ISSET(fd,readset){……}

#ifndef _SELECT_H_#define _SELECT_H_#include "wrap.h"#include "client_list.h"#include "server_queue.h"#define SERVER_PORT     6780#define MAXLINE         100#define OPEN_MAX        65535#define TCP_FRAME_SIZE  1200typedef struct{  int sockfd;  // server socket  int port;    // server port  struct sockaddr_in addr; // server addr    int maxi;  // select max  int maxfd;  int aggregate[FD_SETSIZE];   // select aggregation  fd_set allset;  server_queue_t send_queue; // server send data queue to client  server_queue_t recv_queue; // server recv data queue from client  pthread_t send_thread;  pthread_t recv_thread;  client_t *client;  // client list -- save all client info} server_t;/* recv and send queue frame */typedef struct{  int sockfd;  // client socket  uint16_t length;  char data[TCP_FRAME_SIZE];} __packed tcp_frame_t;//==========================================================server_t *SocketInit(void);#endif /* _SELECT_H_ */

#include "select.h"#include "debug.h"static server_t *socket_init(void){  int opt = 1, i;  server_t *current;  current = (server_t *)malloc(sizeof(server_t));  current->port = SERVER_PORT;  current->sockfd = Socket(AF_INET, SOCK_STREAM, 0);  // SOL_SOCKET: port can same, ip not  Setsockopt(current->sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));  current->addr.sin_family = AF_INET;  current->addr.sin_port = htons(current->port);  current->addr.sin_addr.s_addr = INADDR_ANY;  Bind(current->sockfd, (struct sockaddr *)¤t->addr, sizeof(current->addr));  Listen(current->sockfd, MAXLINE);  current->maxi = -1;  current->maxfd = current->sockfd;  for(i = 0; i < FD_SETSIZE; ++i)  {    current->aggregate[i] = -1;  }  FD_ZERO(current->allset);  FD_SET(current->sockfd , ¤t->allset);  ServerQueueInit(&current->send_queue, TCP_FRAME_SIZE);  ServerQueueInit(&current->recv_queue, TCP_FRAME_SIZE);  return current;}static void socket_accept(server_t *arg, fd_set *rset){  server_t *current = arg;  struct sockaddr_in addr;  int len = sizeof(struct sockaddr_in), i;  int new_fd = Accept(current->sockfd, (struct sockaddr *)&addr, &len);  debug("new connection client_fd ( %d ) %s: %d\n", new_fd, inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));  for(i = 0; i < FD_SETSIZE; ++i)  {    if(current->aggregate[i] < 0)    {      // add new_fd to aggregate      current->aggregate[i] = new_fd;      break;    }  }  if(FD_SETSIZE == i)  {    printf("too many connects\n");    Close(new_fd);    return;  }  FD_SET(new_fd , current->allset);  if(new_fd > current->maxfd)  {    current->maxfd = new_fd;  }  if(i > current->maxi)  {    current->maxi = i;  }  /* add client node */  client_t *node = (client_t *)malloc(sizeof(client_t));  node->sockfd = new_fd;  memcpy(&node->addr, &addr, sizeof(struct sockaddr_in));  ClientAdd(node);}static void socket_recv(server_t *arg, fd_set *rset, int ret){  server_t *current = arg;  int i, sockfd, length = 0;  tcp_frame_t write;  for(i = 0; i <= current->maxi; ++i)  {    if((sockfd = current->aggregate[i]) < 0)    {      continue;    }    if(FD_ISSET(sockfd , rset))    {      length = recv(sockfd, write.data, TCP_FRAME_SIZE, 0);      if(0 == length)      {        /* delete client node, close connect socket */        debug("client[%d] close\n", sockfd);        ClientDel(sockfd);        Close(sockfd);        FD_CLR(sockfd , current->allset);        current->aggregate[i] = -1;        continue;      }      else if(length > 0)      {        write.sockfd = sockfd;        write.length = length;        server_debug(write.data, write.length);        // add data to recv_queue, pop in other,        if(ServerQueueWrite(&current->recv_queue, (uint8_t *)&write, sizeof(tcp_frame_t)) == 0)        {          debug("push failure...queue full...\n");        }      }      if(--ret <= 0)      {        break;      }    }  }}static void *server_recv_thread(void *arg){  server_t *current = (server_t *)arg;  fd_set rset;  struct timeval timeout;  while(1)  {    rset = current->allset;    timeout.tv_sec = 0;    timeout.tv_usec = 200;    int ret = Select(current->maxfd + 1 , &rset, NULL , NULL , &timeout);    if(0 == ret)    {      continue;    }    if(FD_ISSET(current->sockfd, &rset))    {      socket_accept(current, &rset); // a new connect come    }    if(--ret < 0)    {      continue;    }    socket_recv(current, &rset, ret); // a exsit connect send data to us  }  Close(current->sockfd);  return NULL;}static void *server_send_thread(void *arg){  server_t *current = (server_t *)arg;  tcp_frame_t *read = NULL;  while(1)  {    //read = (tcp_frame_t*)ServerQueueRead(&current->send_queue, sizeof(tcp_frame_t));    if(read != NULL)    {      //server_debug(read->data, read->length);    }    usleep(100);  }  return NULL;}server_t * SocketInit(void){  server_t *current = socket_init();  debug("create thread...\r\n");  pthread_create(&current->send_thread, NULL, server_send_thread, current);  pthread_create(&current->recv_thread, NULL, server_recv_thread, current);  return current;}