Linux C高级io-有限状态机

1，非阻塞io

流程图：1，rl-wr-rr-wl 可以变换成 2，rl-wr rr-wl

#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define TTY1 "/dev/tty11"
#define TTY2 "/dev/tty12"

#define BUFSIZE 1024

enum 
{
	STATE_R=1,
	STATE_W,
	STATE_E,
	STATE_T
};

struct fsm_st
{
	int state;
	int sfd;
	int dfd;
	char buf[BUFSIZE];
	int len;
	int pos;
	char *errstr;
};

void fsm_driver(struct fsm_st *fsm)
{
	int ret;
	switch(fsm->state)
	{
		case STATE_R:
			ret = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(ret == 0)
			{
				fsm->state = STATE_T;
			}
			else{
				fsm->state = STATE_W;
				fsm->len = ret;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
				 if(ret < fsm->len)
				 {
					 fsm->pos += ret;
					 fsm->len -= ret;
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;
		case STATE_E:
				perror(fsm->errstr);
				fsm->state = STATE_T;
			break;
		case STATE_T:
			break;
		default:
			abort();				
	}
	
}

void relay(int fd1, int fd2)
{
	int fd1_save, fd2_save;
	struct fsm_st fsm12, fsm21;
	
	fd1_save = fcntl(fd1, F_GETFL);
	fcntl(fd1, F_SETFL, fd1_save | O_NONBLOCK);
	
	fd2_save = fcntl(fd2, F_GETFL);
	fcntl(fd2, F_SETFL, fd2_save | O_NONBLOCK);
	
	fsm12.state = STATE_R;
	fsm12.sfd = fd1;
	fsm12.dfd = fd2;
	
	fsm21.state = STATE_R;
	fsm21.sfd = fd2;
	fsm21.dfd = fd1;
	
	while(fsm12.state != STATE_T || fsm21.state != STATE_T)
	{
		fsm_driver(&fsm12);
		fsm_driver(&fsm21);
	}
	
	
	fcntl(fd1, F_SETFL, fd1_save);
	fcntl(fd2, F_SETFL, fd2_save);
}

int main()
{
	int fd1, fd2;
	
	fd1 = open(TTY1, O_RDWR);
	if(fd1 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd1, "TTY1n", 5);
	
	fd2 = open(TTY2, O_RDWR);
	if(fd2 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd2, "TTY2n", 5);
	
	relay(fd1, fd2);
	
	close(fd1);
	close(fd2);
	exit(0);
	
}

注意运行时要加上sudo权限，切换tty11和tty12要用到ctrl+alt+f11/f12

读写那一块代码可以优化下

        case STATE_R:
			fsm->len = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(fsm->len < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(fsm->len == 0)
			{
				fsm->state = STATE_T;
			}
			else
            {
				fsm->state = STATE_W;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
                 fsm->pos += ret;
				 fsm->len -= ret;
				 if(fsm->len != 0)
				 {
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;

上述程序由于一直在忙读，读没有数据返回errno(EAGAIN)，所以程序所占用cpu核很多。

2 采用select多路复用

以事件为单位，监听文件描述符。

select返回时，监视现场不再是原来的了，会被清空。因为监视现场和监视结果放在同一个空间

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define TTY1 "/dev/tty2"
#define TTY2 "/dev/tty3"

#define BUFSIZE 1024

enum 
{
	STATE_R=1,
	STATE_W,
	STATE_AUTO, //由于select 只能监听读写变化，
	STATE_E,
	STATE_T
};

struct fsm_st
{
	int state;
	int sfd;
	int dfd;
	char buf[BUFSIZE];
	int len;
	int pos;
	char *errstr;
};

void fsm_driver(struct fsm_st *fsm)
{
	int ret;
	switch(fsm->state)
	{
		case STATE_R:
			ret = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(ret == 0)
			{
				fsm->state = STATE_T;
			}
			else{
				fsm->state = STATE_W;
				fsm->len = ret;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
				 if(ret < fsm->len)
				 {
					 fsm->pos += ret;
					 fsm->len -= ret;
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;
		case STATE_E:
				perror(fsm->errstr);
				fsm->state = STATE_T;
			break;
		case STATE_T:
			break;
		default:
			abort();				
	}
	
}

static int max(int a, int b)
{
	if(a > b)
		return a;
	return b;
}

void relay(int fd1, int fd2)
{
	int fd1_save, fd2_save;
	struct fsm_st fsm12, fsm21;
	fd_set rdset, wrset;
	
	fd1_save = fcntl(fd1, F_GETFL);
	fcntl(fd1, F_SETFL, fd1_save | O_NONBLOCK);
	
	fd2_save = fcntl(fd2, F_GETFL);
	fcntl(fd2, F_SETFL, fd2_save | O_NONBLOCK);
	
	fsm12.state = STATE_R;
	fsm12.sfd = fd1;
	fsm12.dfd = fd2;
	
	fsm21.state = STATE_R;
	fsm21.sfd = fd2;
	fsm21.dfd = fd1;
	
	while(fsm12.state != STATE_T || fsm21.state != STATE_T)
	{
		FD_ZERO(&rdset);
		FD_ZERO(&wrset);
		
		if(fsm12.state == STATE_R)
			FD_SET(fsm12.sfd, &rdset);  // 有事情才去监听，不是加上所有的
		if(fsm12.state == STATE_W)
			FD_SET(fsm12.dfd, &wrset);
		if(fsm21.state == STATE_R)
			FD_SET(fsm21.sfd, &rdset);
		if(fsm21.state == STATE_W)
			FD_SET(fsm21.dfd, &wrset);
		
		if(fsm12.state < STATE_AUTO || fsm21.state < STATE_AUTO)
		{
			if (select(max(fd1, fd2) +1, &rdset, &wrset, NULL, NULL)  < 0) // 最大文件描述符+1
			{
				if(errno == EINTR)
					continue;
				perror("select");
				exit(1);
			}
		}
		
		if(FD_ISSET(fsm12.sfd, &rdset)||FD_ISSET(fsm12.dfd, &wrset)||fsm12.state > STATE_AUTO)
			fsm_driver(&fsm12);
		if(FD_ISSET(fsm21.sfd, &rdset)||FD_ISSET(fsm21.dfd, &wrset)||fsm21.state > STATE_AUTO)
			fsm_driver(&fsm21);
	}
	
	
	fcntl(fd1, F_SETFL, fd1_save);
	fcntl(fd2, F_SETFL, fd2_save);
}

int main()
{
	int fd1, fd2;
	
	fd1 = open(TTY1, O_RDWR);
	if(fd1 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd1, "TTY1n", 5);
	
	fd2 = open(TTY2, O_RDWR);
	if(fd2 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd2, "TTY2n", 5);
	
	relay(fd1, fd2);
	
	close(fd1);
	close(fd2);
	exit(0);
	
}

3，poll多路复用

以文件描述符为单位组织事件

poll里面的文件描述符数组，用来组织事件

事件是一个short长度的位图，所以要按位&发现事件，|来置位事件

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define TTY1 "/dev/tty2"
#define TTY2 "/dev/tty3"

#define BUFSIZE 1024

enum 
{
	STATE_R=1,
	STATE_W,
	STATE_AUTO, //由于select 只能监听读写变化，
	STATE_E,
	STATE_T
};

struct fsm_st
{
	int state;
	int sfd;
	int dfd;
	char buf[BUFSIZE];
	int len;
	int pos;
	char *errstr;
};

void fsm_driver(struct fsm_st *fsm)
{
	int ret;
	switch(fsm->state)
	{
		case STATE_R:
			ret = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(ret == 0)
			{
				fsm->state = STATE_T;
			}
			else{
				fsm->state = STATE_W;
				fsm->len = ret;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
				 if(ret < fsm->len)
				 {
					 fsm->pos += ret;
					 fsm->len -= ret;
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;
		case STATE_E:
				perror(fsm->errstr);
				fsm->state = STATE_T;
			break;
		case STATE_T:
			break;
		default:
			abort();				
	}
	
}

static int max(int a, int b)
{
	if(a > b)
		return a;
	return b;
}

void relay(int fd1, int fd2)
{
	int fd1_save, fd2_save;
	struct fsm_st fsm12, fsm21;
	struct pollfd pfd[2];
	
	fd1_save = fcntl(fd1, F_GETFL);
	fcntl(fd1, F_SETFL, fd1_save | O_NONBLOCK);
	
	fd2_save = fcntl(fd2, F_GETFL);
	fcntl(fd2, F_SETFL, fd2_save | O_NONBLOCK);
	
	fsm12.state = STATE_R;
	fsm12.sfd = fd1;
	fsm12.dfd = fd2;
	
	fsm21.state = STATE_R;
	fsm21.sfd = fd2;
	fsm21.dfd = fd1;
	
	pfd[0].fd = fd1;
	pfd[1].fd = fd2;
	
	while(fsm12.state != STATE_T || fsm21.state != STATE_T)
	{
		pfd[0].events = 0;
		pfd[1].events = 0;
		if(fsm12.state == STATE_R)
			pfd[0].events |= POLLIN;
		if(fsm12.state == STATE_W)
			pfd[1].events |= POLLOUT;
		if(fsm21.state == STATE_R)
			pfd[1].events |= POLLIN;
		if(fsm21.state == STATE_W)
			pfd[0].events |= POLLOUT;
		
		if(fsm12.state < STATE_AUTO || fsm21.state < STATE_AUTO)
		{
			while(poll(pfd, 2, -1) < 0) // 最大文件描述符+1
			{
				if(errno == EINTR)
					continue;
				perror("select");
				exit(1);
			}
		}
		
		if( pfd[0].revents & POLLIN || pfd[1].revents & POLLOUT||fsm12.state > STATE_AUTO)
			fsm_driver(&fsm12);
		if( pfd[1].revents & POLLIN || pfd[0].revents & POLLOUT||fsm21.state > STATE_AUTO)
			fsm_driver(&fsm21);
	}
	
	
	fcntl(fd1, F_SETFL, fd1_save);
	fcntl(fd2, F_SETFL, fd2_save);
}

int main()
{
	int fd1, fd2;
	
	fd1 = open(TTY1, O_RDWR);
	if(fd1 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd1, "TTY1n", 5);
	
	fd2 = open(TTY2, O_RDWR);
	if(fd2 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd2, "TTY2n", 5);
	
	relay(fd1, fd2);
	
	close(fd1);
	close(fd2);
	exit(0);
	
}

4，epoll多路复用

以文件描述符为单位，监听事件

epoll把poll文件描述符数组封装到了kernel上，并提供epoll方法

epoll_create(int size) size不是数组（poll文件描述符数组）大小，正数就可以了。返回的是epoll文件描述符。

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define TTY1 "/dev/tty12"
#define TTY2 "/dev/tty13"

#define BUFSIZE 1024

enum 
{
	STATE_R=1,
	STATE_W,
	STATE_AUTO, //由于select 只能监听读写变化，
	STATE_E,
	STATE_T
};

struct fsm_st
{
	int state;
	int sfd;
	int dfd;
	char buf[BUFSIZE];
	int len;
	int pos;
	char *errstr;
};

void fsm_driver(struct fsm_st *fsm)
{
	int ret;
	switch(fsm->state)
	{
		case STATE_R:
			ret = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(ret == 0)
			{
				fsm->state = STATE_T;
			}
			else{
				fsm->state = STATE_W;
				fsm->len = ret;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
				 if(ret < fsm->len)
				 {
					 fsm->pos += ret;
					 fsm->len -= ret;
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;
		case STATE_E:
				perror(fsm->errstr);
				fsm->state = STATE_T;
			break;
		case STATE_T:
			break;
		default:
			abort();				
	}
	
}

static int max(int a, int b)
{
	if(a > b)
		return a;
	return b;
}

void relay(int fd1, int fd2)
{
	int fd1_save, fd2_save;
	struct fsm_st fsm12, fsm21;
	int epfd;
	struct epoll_event ev;
	
	fd1_save = fcntl(fd1, F_GETFL);
	fcntl(fd1, F_SETFL, fd1_save | O_NONBLOCK);
	
	fd2_save = fcntl(fd2, F_GETFL);
	fcntl(fd2, F_SETFL, fd2_save | O_NONBLOCK);
	
	fsm12.state = STATE_R;
	fsm12.sfd = fd1;
	fsm12.dfd = fd2;
	
	fsm21.state = STATE_R;
	fsm21.sfd = fd2;
	fsm21.dfd = fd1;
	
	epfd = epoll_create(10);
	if(epfd < 0)
	{
		perror("epoll_create");
		exit(1);
	}
	
	ev.events = 0;
	ev.data.fd = fd1;
	epoll_ctl(epfd, EPOLL_CTL_ADD, fd1, &ev);
	
	ev.events = 0;
	ev.data.fd = fd2;
	epoll_ctl(epfd, EPOLL_CTL_ADD, fd2, &ev);
	
	while(fsm12.state != STATE_T || fsm21.state != STATE_T)
	{
		ev.data.fd = fd1;
		ev.events = 0;
		if(fsm12.state == STATE_R)
			ev.events |= EPOLLIN;
		if(fsm21.state == STATE_W)
			ev.events |= EPOLLOUT;
		epoll_ctl(epfd, EPOLL_CTL_MOD, fd1, &ev);
		
		ev.data.fd = fd2;
		ev.events = 0;
		if(fsm21.state == STATE_R)
			ev.events |= EPOLLIN;
		if(fsm12.state == STATE_W)
			ev.events |= EPOLLOUT;
		epoll_ctl(epfd, EPOLL_CTL_MOD, fd2, &ev);
			
		
		if(fsm12.state < STATE_AUTO || fsm21.state < STATE_AUTO)
		{
			while(epoll_wait(epfd, &ev, 2, -1) < 0) // 最大文件描述符+1
			{
				if(errno == EINTR)
					continue;
				perror("select");
				exit(1);
			}
		}
		
		if( (ev.data.fd == fd1 && ev.events == EPOLLIN) || (ev.data.fd == fd2 && ev.events == EPOLLOUT)||fsm12.state > STATE_AUTO)
			fsm_driver(&fsm12);
		if( (ev.data.fd == fd2 && ev.events == EPOLLIN) || (ev.data.fd == fd1 && ev.events == EPOLLOUT)||fsm21.state > STATE_AUTO)
			fsm_driver(&fsm21);
	}
	
	
	fcntl(fd1, F_SETFL, fd1_save);
	fcntl(fd2, F_SETFL, fd2_save);
	close(epfd);
}

int main()
{
	int fd1, fd2;
	
	fd1 = open(TTY1, O_RDWR);
	if(fd1 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd1, "TTY1n", 5);
	
	fd2 = open(TTY2, O_RDWR);
	if(fd2 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd2, "TTY2n", 5);
	
	relay(fd1, fd2);
	
	close(fd1);
	close(fd2);
	exit(0);
	
}

6，中继引擎

忙等状态，因为一直在轮训，轮序查看每个读写状态机，每个状态机都推动一次。

主程序要pause()停止，否则程序就停止工作了。开启的线程不断在工作，跟前面的用多线程实现mytbf一样，线程工作。

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include "relay.h"

#define BUFSIZE 1024

enum 
{
	STATE_R=1,
	STATE_W,
	STATE_E,
	STATE_T
};

enum
{
	STATE_RUNNING=1,
	STATE_CANCELED,
	STATE_OVER
};

struct fsm_st
{
	int state;
	int sfd;
	int dfd;
	char buf[BUFSIZE];
	int len;
	int pos;
	char *errstr;
};

struct rel_job_st
{
	int fd1, fd2;
	int job_state;
	struct fsm_st fsm12, fsm21;
	int fd1_save, fd2_save;
};

static struct rel_job_st *rel_job[REL_JOBMAX];
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
static pthread_once_t once_init=PTHREAD_ONCE_INIT;

void fsm_driver(struct fsm_st *fsm)
{
	int ret;
	switch(fsm->state)
	{
		case STATE_R:
			ret = read(fsm->sfd, fsm->buf, BUFSIZE);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_R;
				else
				{
					fsm->errstr = "read()";
					fsm->state = STATE_E;
				}
			}
			else if(ret == 0)
			{
				fsm->state = STATE_T;
			}
			else{
				fsm->state = STATE_W;
				fsm->len = ret;
				fsm->pos = 0;
			}
			break;
		case STATE_W:
			ret = write(fsm->dfd, fsm->buf + fsm->pos, fsm->len);
			if(ret < 0)
			{
				if(errno == EAGAIN)
					fsm->state = STATE_W;
				else
				{
					fsm->errstr = "write()";
					fsm->state = STATE_E;
				}
			}
			else
			{
				 if(ret < fsm->len)
				 {
					 fsm->pos += ret;
					 fsm->len -= ret;
					 fsm->state = STATE_W;
				 }
				 else
					 fsm->state = STATE_R;
			}
			break;
		case STATE_E:
				perror(fsm->errstr);
				fsm->state = STATE_T;
			break;
		case STATE_T:
			break;
		default:
			abort();				
	}
	
}

static int get_pos_unlock()
{
	int i;
	for(i=0; ijob_state == STATE_RUNNING)
				{
					fsm_driver(&rel_job[i]->fsm12);
					fsm_driver(&rel_job[i]->fsm21);
					if(rel_job[i]->fsm12.state == STATE_T && rel_job[i]->fsm21.state == STATE_T)
					{
						rel_job[i]->job_state = STATE_OVER;
					}
				}
			}
		}
		pthread_mutex_unlock(&mtx);
	}
}

static void module_load(void)
{
	printf("%s:%dn", __FUNCTION__, __LINE__);
	int err;
	pthread_t tid_relayer;
	err = pthread_create(&tid_relayer, NULL, thr_worker, NULL);
	if(err)
	{
		fprintf(stderr, "pthread_create():%sn", strerror(err));
		exit(1);
	}
}

int rel_addjob(int fd1, int fd2)
{
	struct rel_job_st *me;
	int pos;
	
	pthread_once(&once_init, module_load);
	
	printf("%s:%dn", __FUNCTION__, __LINE__);
	
	me = malloc(sizeof(*me));
	if(me == NULL)
		return -ENOMEM;
	
	me->fd1 = fd1;
	me->fd2 = fd2;
	me->job_state = STATE_RUNNING;
	
	me->fd1_save = fcntl(me->fd1, F_GETFL);
	fcntl(me->fd1, F_SETFL, me->fd1_save|O_NONBLOCK);
	me->fd2_save = fcntl(me->fd2, F_GETFL);
	fcntl(me->fd2, F_SETFL, me->fd2_save|O_NONBLOCK);
	
	me->fsm12.sfd = me->fd1;
	me->fsm12.dfd = me->fd2;
	me->fsm12.state = STATE_R;
	me->fsm21.sfd = me->fd2;
	me->fsm21.dfd = me->fd1;
	me->fsm21.state = STATE_R;
	
	pthread_mutex_lock(&mtx);
	pos = get_pos_unlock();
	if(pos < 0)
	{
		pthread_mutex_unlock(&mtx);
		fcntl(me->fd1, F_SETFL, me->fd1_save);
		fcntl(me->fd2, F_SETFL, me->fd2_save);
		free(me);
		return -ENOSPC;
	}
	rel_job[pos] = me;
	pthread_mutex_unlock(&mtx);
	return pos;
}

main函数

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "relay.h"

#define TTY1 "/dev/tty9"
#define TTY2 "/dev/tty8"

#define TTY3 "/dev/tty10"
#define TTY4 "/dev/tty11"
int main()
{
	int fd1, fd2, fd3, fd4;
	int job1, job2;
	
	fd1 = open(TTY1, O_RDWR);
	if(fd1 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd1, "TTY1n", 5);
	
	fd2 = open(TTY2, O_RDWR);
	if(fd2 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd2, "TTY2n", 5);
	
	job1 = rel_addjob(fd1, fd2);
	if(job1 <0)
	{
		fprintf(stderr, "rel_addjob():%sn", strerror(-job1));
		exit(1);
	}
	
	//job2
	
	fd3 = open(TTY3, O_RDWR);
	if(fd3 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd3, "TTY3n", 5);
	
	fd4 = open(TTY4, O_RDWR);
	if(fd4 < 0)
	{
		perror("open()");
		exit(1);
	}
	
	write(fd4, "TTY4n", 5);
	
	job2 = rel_addjob(fd3, fd4);
	if(job2 <0)
	{
		fprintf(stderr, "rel_addjob():%sn", strerror(-job2));
		exit(1);
	}
	
	while (1)
		pause();
	
	close(fd1);
	close(fd2);
	close(fd3);
	close(fd4);
	exit(0);
	
}

Linux C高级io-有限状态机

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