Node.js从事件中取消setTimeout

Question

I have some code that polls a service and I need a way to cancel that interval clearTimeout via events. The timeouts act as an interval, calling setTimeout again within the function.

So for example, I have another object that that's exposed as an event emitter and this process polls and emits some data along the way. Here's a simplified example:

function events() {

  var timer = true;
  events.on('cancel', function() {
    timer = false;
  });

  function polling() {
    //Get some data
    events.emit('data', data);

    if (timer || typeof timer == 'number') {
      timer = setTimeout(polling, 1000);
    }
  }

  polling();

}

This can work, basically when this service receives the cancel event, it sets the timer to false, which due to the check it won't continue. However, there could be a chance where it passed the condition, event fired, timer reset and now it continues on.

Any idea if there's a more bulletproof way to handle this kind of thing? Basically canceling the polling based on an event.

Answer 1

However, there could be a chance where it passed the condition, event fired, timer reset and now it continues on.

Nope. Node.js is single-threaded and works by means of an event loop, so nothing can interrupt your running code unless you allow it to (by queuing up and continuing execution in another event, eg with setTimeout or process.nextTick ).

What you should do instead if you want to avoid one more call of polling , though, is use clearTimeout .

function events() {
  var timer = null;

  events.on('cancel', function() {
    clearTimeout(timer);
  });

  function polling() {
    //Get some data
    events.emit('data', data);

    timer = setTimeout(polling, 1000);
  }

  polling();
}