c - 为什么使用 timer_settime() 会影响 sleep() 函数

Question

我正在尝试创建带有回调函数的周期性计时器，它运行良好。但是在 main() 中我有 sleep() 函数，它不能像往常一样工作。它不是休眠 10 秒，而是休眠 500 毫秒，这个时间是为 timer_settime() 函数设置的。这是错误还是正常行为？

volatile sig_atomic_t timer_flag = false;
volatile int total_cnt = 0;
timer_t gTimerid;

void start_timer(void)
{
    struct itimerspec value;
    value.it_value.tv_sec = 0;
    value.it_value.tv_nsec = 500000000;
    value.it_interval.tv_sec = 0;
    value.it_interval.tv_nsec = 500000000;
    timer_create(CLOCK_REALTIME, NULL, &gTimerid);
    timer_settime(gTimerid, 0, &value, NULL);
}

void stop_timer(void)
{
    struct itimerspec value;
    value.it_value.tv_sec = 0;
    value.it_value.tv_nsec = 0;
    value.it_interval.tv_sec = 0;
    value.it_interval.tv_nsec = 0;
    timer_settime(gTimerid, 0, &value, NULL);
}

void timer_callback(int sig) 
{
    timer_flag = true;  
}

static void *count(void *ptr)
{   
    for(;;) {
        if(timer_flag == true) {                    
            timer_flag = false;
            printf("%d\n", total_cnt++);
        }
        usleep(1000);
    }

    return NULL;
}

int main(void)
{   
    (void) signal(SIGALRM, timer_callback);
    start_timer();

    pthread_t thread_cnt;
    int thread_num = 1;

    pthread_create(&thread_cnt, NULL, count, (void*)&thread_num);

    clock_t begin, end;
    double time_spent;
    struct timeval  tv1, tv2;

    for(;;) {
        printf("Main loop\n");
        gettimeofday(&tv1, NULL);           
        sleep(10);
        gettimeofday(&tv2, NULL);
        printf ("Total time = %f seconds\n",
         (double) (tv2.tv_usec - tv1.tv_usec) / 1000000 +
         (double) (tv2.tv_sec - tv1.tv_sec));
    }

    return 0;
}

Answer 1

这是正常的(=按标准工作)。 sleep 是一个可中断的阻塞函数。

Here's what POSIX says about it:

If sleep() returns because the requested time has elapsed, the value returned shall be 0. If sleep() returns due to delivery of a signal, the return value shall be the "unslept" amount (the requested time minus the time actually slept) in seconds.

如果你想不间断地休眠，你需要阻塞信号(或者你需要在第一次调用被打断后的剩余时间内再次休眠，但你可能需要更高分辨率的休眠函数，例如 nanosleep或 clock_nanosleep )。