globalvar_wait_5s.c

Some simple source code to show specific function like mouse and graphic.

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <time.h>
#include <math.h>

void function()
{
unsigned int i,j;
double y;
for(i=0; i<5000; i++)
 for(j=0; j<4000; j++)
	y=1+1;
}

main()
{
int fd, num;
fd_set rfds;
struct timeval tv;
#if 0
time_t t;
struct tm nowtime, *pt=&nowtime;
char *sTime;
struct timeval tpstart, tpend;
float timeuse;

t=time(NULL);
//pt=&nowtime;
pt=localtime(&t);

sTime=asctime(pt);
printf("Now time is %s \n",sTime);

gettimeofday(&tpstart,NULL);
function();
gettimeofday(&tpend,NULL);
timeuse=1000000*(tpend.tv_sec-tpstart.tv_sec)+tpend.tv_usec-tpstart.tv_usec;//1 t.tv_sec = 1000000 t.tv_usec 

timeuse/=1000000;

printf("Used Time:%f\n",timeuse);

#endif

fd = open("/dev/globalvar", O_RDWR, S_IRUSR | S_IWUSR);
if (fd != - 1)
{

	while (1)
	{
	FD_ZERO(&rfds);
	FD_SET(fd, &rfds);
	tv.tv_sec = 2;
	tv.tv_usec = 0;
	
	select(fd + 1, &rfds, NULL, NULL, &tv);

	if (FD_ISSET(fd, &rfds))
	{
		read(fd, &num, sizeof(int));
		printf("The globalvar is %d\n", num);	

		if (num == 0)
		{
			close(fd);
			break;
		}
	}
	else
	printf("No data within 5 seconds.\n");
	}

}
else
{
	printf("device open failure\n");
}
}