How are the timeout IDs allocated?

[espruino-discuss]

Posted at 2014-04-22 by graf

Could someone please explain me how are the IDs allocated? Or even better why it's not like I thought? :)

In this code below I would expect the ledTimer to get the same value (ID) over and over again but that doesn't happen.

var btnPin = BTN;
var ledPin = LED1;
var ledTimer = null;
digitalWrite(ledPin, 0);

var btnWatcher = setWatch(function () {
  if (ledTimer) {
    clearTimeout(ledTimer);
    ledTimer = null;
  }
  digitalWrite(ledPin, 1);
  console.log("before: " + ledTimer);
  ledTimer = setTimeout(function () {
    digitalWrite(ledPin, 0);
    ledTimer = null;
  }, 4000);
  console.log("after: " + ledTimer);
}, btnPin, {repeat: true, edge: "rising", debounce: 70});

Now when I press the button every 5 seconds I get what I expected:

before: null
after: 2
before: null
after: 2
...and so on

But when I press the button every 3 seconds then it's not what I expected:

before: null
after: 2
before: null
after: 4
...and +2 every time

[gfwilliams]

Posted at 2014-04-22 by @gfwilliams

I'm not sure. I had thought the assignment was:

• If no timers, assign '1'
• If there are timers, assign 1 more than the last timer

However I had to write some code to cope with timers being added/removed while handling a timer, and it could be that does some strange things with the numbering...

[espruino-discuss]

Posted at 2014-04-22 by graf

OK so what is the maximum ID this function can return? Is it some huge number in tens of thousands?

[espruino-discuss]

Posted at 2014-04-22 by graf

Turns out setWatch and setTimeout IDs are shared so that's where value 2 is coming from (watch ID is 1).

If I add another watch for btnPin (falling) then the timeout ID has value 3 and it's growing +3 every time. That means the ID's value can grow very fast if I have a bunch of timers/watches that I want to add or remove dynamically.

And that's just the ID's value growing, the number of timers is the same as far as I understand.

[gfwilliams]

Posted at 2014-04-23 by @gfwilliams

The ID can be up to 18446744073709551615 - so I think you're safe! That may change to 4294967296 at some point in the future, but even so I think you'll be fine!

[espruino-discuss]

Posted at 2014-04-23 by graf

Lol now that's reassuring.

[espruino-discuss]

Posted at 2014-04-25 by graf

One more question because this is driving me nuts and I can't find the reason why ledTimer gets incremented at all.

What happens when I clearTimeout(ledTimer) ? Is it set to an empty function so that when it comes to the given time it does nothing, or is it really removed?

Also when I add console.log(process.memory()); at the beginning of watch function then it shows memory usage goes up quite a lot when I press the button before the timeout passed.

The output now looks like that:

{"free":1722,"usage":78,"total":1800,"history":44,"stackEndAddress":536909512,"flash_start":134217728,"flash_binary_end":134432224,"flash_code_start":134443008,"flash_length":262144}
before: null
after: 2
{"free":1695,"usage":105,"total":1800,"history":44,"stackEndAddress":536909512,"flash_start":134217728,"flash_binary_end":134432224,"flash_code_start":134443008,"flash_length":262144}
before: null
after: 4
{"free":1695,"usage":105,"total":1800,"history":44,"stackEndAddress":536909512,"flash_start":134217728,"flash_binary_end":134432224,"flash_code_start":134443008,"flash_length":262144}
before: null
after: 6
> 

[gfwilliams]

Posted at 2014-04-28 by @gfwilliams

When you say clearTimeout(ledTimer) it should totally remove that timeout and free any memory used by it.

Surely the increased memory usage is because there is already a timer allocated, as you hadn't yet freed it with clearTimeout?

[espruino-discuss]

Posted at 2014-04-28 by graf

as you hadn't yet freed it with clearTimeout?

And this is that part that I don't understand :) I AM doing clearTimeout and led behaves like it was removed (timeout is reset) but memory usage and ID numbering suggests otherwise.

[gfwilliams]

Posted at 2014-04-28 by @gfwilliams

Surely you're just dumping the memory usage before you remove the timer?

var btnPin = BTN;
var ledPin = LED1;
var ledTimer = null;
digitalWrite(ledPin, 0);
var btnWatcher = setWatch(function () {
  console.log("--" + process.memory().usage); // <------------------------------
  if (ledTimer) {
    clearTimeout(ledTimer);
    ledTimer = null;
  }
  digitalWrite(ledPin, 1);
  console.log("before: " + ledTimer);
  ledTimer = setTimeout(function () {
    digitalWrite(ledPin, 0);
    ledTimer = null;
  }, 4000);
  console.log("after: " + ledTimer);
}, btnPin, {repeat: true, edge: "rising", debounce: 70});

--79
before: null
after: 2
--106
before: null
after: 4
--107
before: null
after: 6
--107
before: null
after: 8

Try this:

var btnPin = BTN;
var ledPin = LED1;
var ledTimer = null;
digitalWrite(ledPin, 0);
var btnWatcher = setWatch(function () {  
  if (ledTimer) {
    clearTimeout(ledTimer);
    ledTimer = null;
  }
  console.log("--" + process.memory().usage); // <------------------------------
  digitalWrite(ledPin, 1);
  console.log("before: " + ledTimer);
  ledTimer = setTimeout(function () {
    digitalWrite(ledPin, 0);
    ledTimer = null;
  }, 4000);
  console.log("after: " + ledTimer);
}, btnPin, {repeat: true, edge: "rising", debounce: 70});

--79
before: null
after: 2
--80
before: null
after: 4
--80
before: null
after: 6
--80
before: null
after: 8
--80
before: null
after: 10

[espruino-discuss]

Posted at 2014-04-28 by graf

Surely you're just dumping the memory usage before you remove the timer?

Ahhh good catch, thanks! But it was also before I add another timer..

EDIT: That's it! On the first console.log the memory usage was lower because timer was not even set at this point. Then on the second console.log the timer was finally set and memory usage was higher. Thanks for helping me understand this :)

Now it's only the ID numbering that puzzles me.