如何在一个间隔内停止多次调用一个函数？

Question

How could I ensure that one one call of a function in an interval can run at once?

My code looks like this:

var promisePutTestQuestion;

   onEnter: ['$interval', 'questionService',
             ($interval, qus: IQuestionService) => {
      promisePutTestQuestion = $interval(() => {
         qus.putTestQuestionResponses();
      }, 5 * 1000);
   }],
   onExit: ['$interval',
            ($interval) => {
             $interval.cancel(promisePutTestQuestion);             
   }],

The problem I am having is if the putTestQuestionResponse (which returns a promise) is slow then I have multiple putTestQuestionResponse function calls one after the other.

Would appreciate if anyone has any ideas on this. Thanks

Answer 1

In javascript it's safe to use state variable for this purpose. Whenever qus.putTestQuestionResponses operation takes a lot of time next call will be skipped. So just maintain right state of processing variable, and if it's true quit the interval callback without running task again.

var promisePutTestQuestion;
let processing = false;

onEnter: ['$interval', 'questionService',
         ($interval, qus: IQuestionService) => {
  promisePutTestQuestion = $interval(() => {
     if (processing)
         return;
     processing = true;
     qus.putTestQuestionResponses()
     .then(() => processing = false)
  }, 5 * 1000);
}],
onExit: ['$interval', ($interval) => {
        $interval.cancel(promisePutTestQuestion);
}]

Not sure what promise framework you're using, but () => processing = false should be either in finally() for $q I guess, and in the then that should be after catch to ensure it is executed in any case. So one of these:

qus.putTestQuestionResponses().finally(() => processing = false)

or

qus.putTestQuestionResponses().catch(...).then(() => processing = false)`

or even

qus.putTestQuestionResponses().then(() => processing = false).catch(() => processing = false)