以下代码定期休眠到预期时间点(ts
),并立即获取系统时间(tm2
)。ts
为什么在和之间存在固定时间误差(~52us)tm2
,因为两个时间点相邻。
运行环境是实时打补丁的linux,如果我改变周期性时间间隔的大小,固定时间误差几乎没有变化。
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define US 100 /* sleep US micro-seconds */
#define LOOP 20
double delayed[LOOP];
int main(void)
{
int loop = 0;
struct timespec tm1, tm2, tm2_old;
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &tm1);
ts.tv_sec = tm1.tv_sec;
ts.tv_nsec = tm1.tv_nsec;
while(1){
ts.tv_nsec = ts.tv_nsec + US * 1000L;
ts.tv_sec = ts.tv_sec + (ts.tv_nsec)/1000000000L;
ts.tv_nsec = (ts.tv_nsec)%1000000000;
clock_gettime(CLOCK_MONOTONIC, &tm1);
clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &ts, NULL);
clock_gettime(CLOCK_MONOTONIC, &tm2);
delayed[loop] = (tm2.tv_sec-ts.tv_sec)*1000000.0 + \
(tm2.tv_nsec - ts.tv_nsec)/1000.0;
++loop;
if(loop >= LOOP) break;
}
for(int ii=0; ii<LOOP; ++ii){
printf("delayed %4.2f\n", delayed[ii]);
}
}
运行结果:
delayed 55.62
delayed 53.02
delayed 52.47
delayed 52.30
delayed 52.25
delayed 52.32
delayed 52.30
delayed 52.45
delayed 52.28
delayed 52.29
delayed 52.16
delayed 52.16
delayed 52.19
delayed 52.28
delayed 52.26
delayed 52.23
delayed 52.24
delayed 52.26
delayed 52.32
delayed 52.15