Timer Wheel

timer-wheel is a library for JavaScript and TypeScript for efficiently managing the expiration of a large amount of items. It allows you to schedule items to be expired after a certain delay and then control when to advance and handle the expired items.

This implementation is designed for larger delays and has a minimum delay of 1000 ms.

import { TimerWheel } from 'timer-wheel';

const wheel = new TimerWheel<any>();
wheel.schedule('data', 1500 /* ms */)

// Call `advance()` to advance the wheel and run actions
setInterval(() => {
  const expired = wheel.advance();
  for(const data of expired) {
    // Do something with the expired data
  }
}, 1000);

This library is useful for things like expiring caches with lazy expiration, instead of checking if every cache item should be expired use a wheel to queue removal actions and call advance before every get/set. This is how Transitory implements expiring caches.

Rescheduling

By default TimerWheel will schedule the same object to expired more than once. This will schedule obj to be expired both after 1 and 5 seconds:

const wheel = new TimerWheel();
const obj = {};

// Schedule to be expired after 1 seconds
wheel.schedule(obj, 1000);

// Schedule to also be expired after 5 seconds
wheel.schedule(obj, 5000);

If you want to be able to reschedule when an item expires use ReschedulingTimerWheel:

import { ReschedulingTimerWheel } from 'timer-wheel';

const wheel = new ReschedulingTimerWheel();

const obj = {};

// First schedule at 1 second
wheel.schedule(obj, 1000);

// Replace first scheduling with a new one after 5 seconds
wheel.schedule(obj, 5000);

Running actions

There's a wheel designed to run actions available:

import { ActionTimerWheel } from 'timer-wheel';

const wheel = new ActionTimerWheel();

wheel.schedule(() => {
  /* do something here */
}, 8000);

// Advance the wheel to run expired actions
wheel.advance();