select函式(一)
阿新 • • 發佈:2018-12-13
#include <sys/select.h>
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
引數:
- nfds:監控的檔案描述符集裡最大檔案描述符加1,因為此引數會告訴核心檢測前多少個檔案檔案描述符
- readfs:監控有讀資料到達檔案描述符集合,傳入傳出引數
- writefds:監控寫資料到達檔案描述符集合,傳入傳出引數
- exceptfds:監控異常發生到達檔案描述符集合,如帶外資料到達異常,傳入傳出引數
- timeout:定時阻塞監控時間。
#include <sys/select.h>
void FD_CLR(int fd, fd_set *set); //把檔案描述符集裡fd位清0
int FD_ISSET(int fd, fd_set *set); //測試檔案描述符集裡fd是否置1
void FD_SET(int fd, fd_set *set); //把檔案描述符集合裡fd位置1
void FD_ZERO(fd_set *set); //把檔案描述符集合裡所有位清0
二、select函式用法圖解
三、實驗一
#include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <errno.h> #include <sys/socket.h> void perr_exit(const char *s) { perror(s); exit(-1); } int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr) { int n; again: if ((n = accept(fd, sa, salenptr)) < 0) { //ECONNABORTED 發生在重傳(一定次數)失敗後,強制關閉套接字 //EINTR 程序被訊號中斷 if ((errno == ECONNABORTED) || (errno == EINTR)) { goto again; } else { perr_exit("accept error"); } } return n; } int Bind(int fd, const struct sockaddr *sa, socklen_t salen) { int n; if ((n = bind(fd, sa, salen)) < 0) { perr_exit("bind error"); } return n; } int Connect(int fd, const struct sockaddr *sa, socklen_t salen) { int n; n = connect(fd, sa, salen); if (n < 0) { perr_exit("connect error"); } return n; } int Listen(int fd, int backlog) { int n; if ((n = listen(fd, backlog)) < 0) { perr_exit("listen error"); } return n; } int Socket(int family, int type, int protocol) { int n; if ((n = socket(family, type, protocol)) < 0) { perr_exit("socket error"); } return n; } ssize_t Read(int fd, void *ptr, size_t nbytes) { ssize_t n; again: if ( (n = read(fd, ptr, nbytes)) == -1) { if (errno == EINTR) goto again; else return -1; } return n; } ssize_t Write(int fd, const void *ptr, size_t nbytes) { ssize_t n; again: if ((n = write(fd, ptr, nbytes)) == -1) { if (errno == EINTR) goto again; else return -1; } return n; } int Close(int fd) { int n; if ((n = close(fd)) == -1) perr_exit("close error"); return n; } /*參三: 應該讀取的位元組數*/ //socket 4096 readn(cfd, buf, 4096) nleft = 4096-1500 ssize_t Readn(int fd, void *vptr, size_t n) { size_t nleft; //usigned int 剩餘未讀取的位元組數 ssize_t nread; //int 實際讀到的位元組數 char *ptr; ptr = vptr; nleft = n; //n 未讀取位元組數 while (nleft > 0) { if ((nread = read(fd, ptr, nleft)) < 0) { if (errno == EINTR) //在讀取到資料以前呼叫被訊號所中斷 { nread = 0; } else { return -1; } } else if (nread == 0) { break; } nleft -= nread; //nleft = nleft - nread ptr += nread; } return n - nleft; } ssize_t Writen(int fd, const void *vptr, size_t n) { size_t nleft; ssize_t nwritten; const char *ptr; ptr = vptr; nleft = n; while (nleft > 0) { if ( (nwritten = write(fd, ptr, nleft)) <= 0) { if (nwritten < 0 && errno == EINTR) nwritten = 0; else return -1; } nleft -= nwritten; ptr += nwritten; } return n; } static ssize_t my_read(int fd, char *ptr) { static int read_cnt; static char *read_ptr; static char read_buf[100]; if (read_cnt <= 0) { again: if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) //"hello\n" { if (errno == EINTR) goto again; return -1; } else if (read_cnt == 0) return 0; read_ptr = read_buf; } read_cnt--; *ptr = *read_ptr++; return 1; } /*readline --- fgets*/ //傳出引數 vptr ssize_t Readline(int fd, void *vptr, size_t maxlen) { ssize_t n, rc; char c, *ptr; ptr = vptr; for (n = 1; n < maxlen; n++) { if ((rc = my_read(fd, &c)) == 1) //ptr[] = hello\n { *ptr++ = c; if (c == '\n') break; } else if (rc == 0) { *ptr = 0; return n-1; } else return -1; } *ptr = 0; return n; }
#ifndef __WRAP_H_
#define __WRAP_H_
void perr_exit(const char *s);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
int Bind(int fd, const struct sockaddr *sa, socklen_t salen);
int Connect(int fd, const struct sockaddr *sa, socklen_t salen);
int Listen(int fd, int backlog);
int Socket(int family, int type, int protocol);
ssize_t Read(int fd, void *ptr, size_t nbytes);
ssize_t Write(int fd, const void *ptr, size_t nbytes);
int Close(int fd);
ssize_t Readn(int fd, void *vptr, size_t n);
ssize_t Writen(int fd, const void *vptr, size_t n);
ssize_t my_read(int fd, char *ptr);
ssize_t Readline(int fd, void *vptr, size_t maxlen);
#endif
- 服務端server.c
//server.c
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/select.h>
#include "wrap.h"
#define SERV_PROT 6666
int main(int argc, char *argv[])
{
int i, j, n, nread;
int maxfd = 0;
int listenfd, connfd;
char buf[BUFSIZ];
struct sockaddr_in clie_addr, serv_addr;
socklen_t clie_addr_len;
listenfd = Socket(AF_INET, SOCK_STREAM, 0);
int opt = 1;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(SERV_PROT);
Bind(listen, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
Listen(listenfd, 128);
fd_set rset, allset;
maxfd = listenfd;
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
while (1)
{
rset = allset;
nread = select(maxfd + 1, &rset, NULL, NULL, NULL); //每次迴圈都從新設定select監控訊號集
if(nread < 0)
perr_exit("select error");
if (FD_ISSET(listenfd, &rset)) //說明有新的客戶端連線請求
{
clie_addr_len = sizeof(clie_addr);
connfd = Accept(listenfd, (struct sockaddr *)&clie_addr, &clie_addr_len);
FD_SET(connfd, &allset); //向監控檔案描述符集合allset新增新的檔案描述符connfd
if (maxfd < connfd)
maxfd = connfd;
if (0 == --nread) //說明select只返回一個,並且listenfd,後續執行無須執行
continue;
}
for (i = listenfd + 1; i <= maxfd; i++)
{
if (FD_ISSET(i, &rset))
{
if ((n = Read(i, buf, sizeof(buf))) == 0) //當client關閉連結時, 服務端也關閉對應連結
{
Close(i);
FD_CLR(i, &allset); //解除select對此檔案描述符的監控
}
else if(n == -1)
perr_exit("read error");
for (j = 0; j < n; ++j)
buf[j] = toupper(buf[j]);
Write(i, buf, n);
}
}
}
Close(listenfd);
return 0;
}
- 客戶端:clent.c
#include <arpa/inet.h>
#include "wrap.h"
#define SERV_IP "192.168.245.139"
#define SERV_PORT 6666
int main(void)
{
int sfd, len;
struct sockaddr_in serv_addr;
char buf[BUFSIZ];
sfd = Socket(AF_INET, SOCK_STREAM, 0);
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr.s_addr);
serv_addr.sin_port = htons(SERV_PORT);
Connect(sfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
while (1)
{
fgets(buf, sizeof(buf), stdin);
int r = Write(sfd, buf, strlen(buf));
printf("Write r ======== %d\n", r);
len = Read(sfd, buf, sizeof(buf));
printf("Read len ========= %d\n", len);
Write(STDOUT_FILENO, buf, len);
}
Close(sfd);
return 0;
}
- 公共標頭檔案集程式:wrap.h、wrap.c
輸出結果:
客戶端:
服務端: