usleep 不准确,本来想slepp 50us, 但结果是20ms
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
int main(void)
{
struct timezone tz;
struct timeval now;
for(int i=0; i<100000; i++)
{
usleep(50);
gettimeofday(&now, &tz);
printf("%d, %d.%d\n",i, now.tv_sec, now.tv_usec);
}
return(1);
}