以特定时间间隔执行函数 [英] Executing a function at specific intervals

问题描述

任务是每 x(比如 x=10)秒执行一个函数(比如 Processfunction()).

The task is to execute a function (say Processfunction()) every x (say x=10) seconds.

使用下面的代码，我可以每 x 秒调用一次 Processfunction().

With below code, I'm able to call Processfunction() every x seconds.

问题:函数执行时间超过10秒的情况如何处理?

Question: How to handle the case where the function takes more than 10 seconds to finish execution?

一种方法是使用一个标志来指示 Processfunction() 执行的结束并在调用 Processfunction() 之前检查它.有一个更好的方法吗 ?

One way would be to have a flag to indicate the end of Processfunction() execution and check for it before calling Processfunction(). Is there a better way to do this ?

#include <pthread.h>
#include <unistd.h> // for sleep() and usleep()

void *timerthread(void *timer_parms) {  

  struct itimerspec new_value;
  int max_exp, fd;
  struct timespec now;
  uint64_t exp;
  ssize_t s;

  struct timer_params *p =(struct timer_params*)timer_parms;

  printf("starttimer Start\n");
  /* Create a CLOCK_REALTIME absolute timer with initial
     expiration and interval as specified in command line */
  if (clock_gettime(CLOCK_REALTIME, &now) == -1)
    handle_error("clock_gettime");

  new_value.it_value.tv_sec = now.tv_sec;
  new_value.it_value.tv_nsec = now.tv_nsec + p->tv_nsec;
  new_value.it_interval.tv_sec = p->tv_sec;
  new_value.it_interval.tv_nsec = p->tv_nsec;
  //max_exp = 5; //No of times

  fd = timerfd_create( CLOCK_REALTIME , 0);
  if (fd == -1)
    handle_error("timerfd_create");

  if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1)
    handle_error("timerfd_settime");

  printf("timer started\n");

  while(1) // keep checking
  {
    s = read(fd, &exp, sizeof(uint64_t));
    if (s != sizeof(uint64_t))
      handle_error("read");
    Processfunction(); // Say after X seconds call this function
  }
  return NULL;
}

int main() {

  struct timer_params timer_params_obj;
  int res;void *thread_result;
  timer_params_obj.tv_sec = 10; 
  //timer_params_obj.tv_nsec = 10000000  ; //10ms
  timer_params_obj.tv_nsec = 0  ; 

  pthread_t pt;
  pthread_create(&pt, NULL, timerthread, &timer_params_obj);
  // thread is running and will call Processfunction() every 10 sec
}

推荐答案

为什么需要计时器?

您可以只测量执行时间并根据经过时间与所需间隔持续时间的关系进行睡眠.

You could just measure the execution time and take a sleep according to the relation of elapsed time to desired interval duration.

示例:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

int main() {
    srand(1);
    for (;;) {
        double interval = 10; /* seconds */

        /* start time */
        time_t start = time(NULL);

        /* do something */
        int duration = rand() % 13;
        printf("%2d seconds of work started at %s", duration, ctime(&start));
        sleep(duration);

        /* end time */
        time_t end = time(NULL);

        /* compute remaining time to sleep and sleep */
        double elapsed = difftime(end, start);
        int seconds_to_sleep = (int)(interval - elapsed);
        if (seconds_to_sleep > 0) { /* don't sleep if we're already late */
            sleep(seconds_to_sleep);
        }
    }
    return 0;
}

输出:

$ gcc test.c && ./a.out
 0 seconds of work started at Sun Mar 17 21:20:28 2013
 9 seconds of work started at Sun Mar 17 21:20:38 2013
11 seconds of work started at Sun Mar 17 21:20:48 2013
 4 seconds of work started at Sun Mar 17 21:20:59 2013
 1 seconds of work started at Sun Mar 17 21:21:09 2013
^C

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