初学socket时, 只会 read, write, 那是阻塞的工作方式, 想和多个socket 工作, 要用到多线程,
今天来学习一下使用select方式进行非阻塞方式的socket交互
核心概念就是使用一个fd_set 去管理所有socket的fd.
select 方法本身是阻塞型的, 但当它管理的从多socket中有一个有读写事件时, 就会返回.
这样做的好处就是一个线程,管理多个socket的io.
- 几个方法
FD_ZERO(&all_set); // 初始化 fd_set
FD_SET(listen_fd, &all_set); // 把fd 添加到 fd_set
FD_ISSET(listen_fd, &r_set); // 检测新fd , 是否已经在 fd_set中存在
FD_CLR(fd, &all_set); 从fd_set中移除一个fd
话不多说, 上代码 :
- wrap.h
//
// Created by gg on 26/12/2019.
//
#ifndef CHAT_WRAP_H
#define CHAT_WRAP_H
void perr_exit(const char *s);
struct sockaddr_in * ServerAddr(int port);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
void Bind(int fd, const struct sockaddr *sa, socklen_t salen);
void Connect(int fd, const struct sockaddr *sa, socklen_t salen);
void 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);
void Close(int fd);
#endif //CHAT_WRAP_H
- wrap.c
//
// Created by gg on 26/12/2019.
//
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include "wrap.h"
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
struct sockaddr_in *ServerAddr(int port) {
struct sockaddr_in *server_addr = (struct sockaddr_in *) malloc(sizeof(struct sockaddr_in));
bzero(server_addr, sizeof(struct sockaddr_in));
server_addr->sin_family = AF_INET;
server_addr->sin_addr.s_addr = htonl(INADDR_ANY);
server_addr->sin_port = htons(port);
return server_addr;
}
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) {
if ((errno == ECONNABORTED) || (errno == EINTR))
goto again;
else
perr_exit("accept error");
}
return n;
}
void Bind(int fd, const struct sockaddr *sa, socklen_t salen) {
if (bind(fd, sa, salen) < 0)
perr_exit("bind error");
}
void Connect(int fd, const struct sockaddr *sa, socklen_t salen) {
if (connect(fd, sa, salen) < 0)
perr_exit("connect error");
}
void Listen(int fd, int backlog) {
if (listen(fd, backlog) < 0)
perr_exit("listen error");
}
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;
}
void Close(int fd) {
if (close(fd) == -1)
perr_exit("close error");
}
- main.c
#pragma clang diagnostic push
#pragma ide diagnostic ignored "hicpp-signed-bitwise"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>
#include "wrap.h"
#define MAX_LINE 80
#define SERVER_PORT 7890
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wmissing-noreturn"
int main(int argc, char *argv[]) {
int i, maxi, maxfd, listen_fd, conn_fd, sock_fd;
int n_ready, client[FD_SETSIZE];
ssize_t n;
/** r_set : read sets, all_set : all i/o sets*/
fd_set r_set, all_set;
char buf[MAX_LINE];
char str[INET_ADDRSTRLEN];
socklen_t cli_addr_len;
struct sockaddr_in cli_addr;
struct sockaddr_in *server_addr;
/** 1. create socket */
listen_fd = Socket(AF_INET, SOCK_STREAM, 0);
server_addr = ServerAddr(SERVER_PORT);
/** 2. bind address and port */
Bind(listen_fd, (struct sockaddr *) server_addr, sizeof(struct sockaddr_in));
free(server_addr);
/** 3. listening on */
Listen(listen_fd, 20);
maxfd = listen_fd;
maxi = -1;
/** init every client fd : -1 */
for (i = 0; i < FD_SETSIZE; i++)
client[i] = -1;
/** 4.1 init all_set */
FD_ZERO(&all_set);
/** 4.2 register server fd to all_set */
FD_SET(listen_fd, &all_set);
printf("Stand by ... \n");
for (;;) {
/** 5.1 copy all_set to read set */
r_set = all_set;
/** 5.2 waiting for client connection ...
* the first param is always the max active socket fd + 1
* first param: "select" will monitor fd io event from 0 to maxfd + 1, the "maxfd + 1" equals the new connection fd
*/
n_ready = select(maxfd + 1, &r_set, NULL, NULL, NULL);
if (n_ready < 0)
perr_exit("select error");
/* new client connection, check listen_fd is readable */
if (FD_ISSET(listen_fd, &r_set)) {
cli_addr_len = sizeof(cli_addr);
conn_fd = Accept(listen_fd, (struct sockaddr *) &cli_addr, &cli_addr_len);
printf("new client_fd : %d receive from %s at PORT %d\n", conn_fd, inet_ntop(AF_INET, &cli_addr.sin_addr, str, sizeof(str)), ntohs(cli_addr.sin_port));
/* add client fd to client array */
for (i = 0; i < FD_SETSIZE; i++)
if (client[i] < 0) {
client[i] = conn_fd;
break;
}
/* max client count exceed */
if (i == FD_SETSIZE) {
fputs("too many clients\n", stderr);
exit(1);
}
/* add to all_set */
FD_SET(conn_fd, &all_set);
if (conn_fd > maxfd)
maxfd = conn_fd;
/* update client count index */
if (i > maxi)
maxi = i;
/* always true ? */
if (--n_ready == 0)
continue;
}
for (i = 0; i <= maxi; i++) { /* check all clients for data */
if ((sock_fd = client[i]) < 0)
continue;
if (FD_ISSET(sock_fd, &r_set)) {
/** close lost socket client */
if ((n = Read(sock_fd, buf, MAX_LINE)) == 0) {
Close(sock_fd);
FD_CLR(sock_fd, &all_set);
client[i] = -1;
}
else {
for (int k = 0; k <= maxi; ++k) {
int client_fd = client[k];
if (client_fd > -1 && client_fd != sock_fd)
Write(client_fd, buf, n);
}
}
if (--n_ready == 0)
break;
}
}
}
return 0;
}
#pragma clang diagnostic pop
#pragma clang diagnostic pop
