overleaf/services/document-updater/app/coffee/RateLimitManager.js

/*
 * decaffeinate suggestions:
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
let RateLimiter;
const Settings = require('settings-sharelatex');
const logger = require('logger-sharelatex');
const Metrics = require('./Metrics');

module.exports = (RateLimiter = class RateLimiter {

	constructor(number) {
		if (number == null) { number = 10; }
		this.ActiveWorkerCount = 0;
		this.CurrentWorkerLimit = number;
		this.BaseWorkerCount = number;
	}

	_adjustLimitUp() {
		this.CurrentWorkerLimit += 0.1; // allow target worker limit to increase gradually
		return Metrics.gauge("currentLimit", Math.ceil(this.CurrentWorkerLimit));
	}

	_adjustLimitDown() {
		this.CurrentWorkerLimit = Math.max(this.BaseWorkerCount, (this.CurrentWorkerLimit * 0.9));
		logger.log({currentLimit: Math.ceil(this.CurrentWorkerLimit)}, "reducing rate limit");
		return Metrics.gauge("currentLimit", Math.ceil(this.CurrentWorkerLimit));
	}

	_trackAndRun(task, callback) {
		if (callback == null) { callback = function() {}; }
		this.ActiveWorkerCount++;
		Metrics.gauge("processingUpdates", this.ActiveWorkerCount);
		return task(err => {
			this.ActiveWorkerCount--;
			Metrics.gauge("processingUpdates", this.ActiveWorkerCount);
			return callback(err);
		});
	}

	run(task, callback) {
		if (this.ActiveWorkerCount < this.CurrentWorkerLimit) {
			this._trackAndRun(task);  // below the limit, just put the task in the background
			callback();         // return immediately
			if (this.CurrentWorkerLimit > this.BaseWorkerCount) {
				return this._adjustLimitDown();
			}
		} else {
			logger.log({active: this.ActiveWorkerCount, currentLimit: Math.ceil(this.CurrentWorkerLimit)}, "hit rate limit");
			return this._trackAndRun(task, err => {
				if ((err == null)) { this._adjustLimitUp(); } // don't increment rate limit if there was an error
				return callback(err);
			}); // only return after task completes
		}
	}
});