TieredLock JS class

TieredLock.js

/**
 * Tiered lock works as a multi-level boolean / mutex.
 *
 * Main use case is to disable page refresh during
 * an ongoing task, when there can be multiple such tasks.
 */
function TieredLock() {
	this._weight = 0;
	this._locks = {};
}


/** Place a lock (optionally named) */
TieredLock.prototype.lock = function (name) {
	if (typeof name == 'undefined') {
		this._weight++;
	} else {
		// init if undefined
		if (typeof this._locks[name] == 'undefined') {
			this._locks[name] = 0;
		}

		this._locks[name]++;
	}
};


/** Release a lock (plain or named) */
TieredLock.prototype.unlock = function (name) {
	if (typeof name == 'undefined') {
		// decrease, but don't go under zero.
		if (this._weight > 0) {
			this._weight--;
		} else {
			console.error('Lock underflow.');
		}
	} else {
		if (this._locks[name] == 0) { // catch both zero & undefined
			this._locks[name] = 0; // normalize to zero
			console.error('Lock "' + name + '" underflow.');
			return;
		}

		this._locks[name]--;
	}
};


/** Check if the resource is locked - at least one lock active */
TieredLock.prototype.isLocked = function () {
	if (this._weight > 0) return true;

	for (var k in this._locks) {
		if (this._locks.hasOwnProperty(k)) {
			// if greater than zero, locked
			if (this._locks[k]) {
				return true;
			}
		}
	}

	return false;
};


/** Debug function - print status to console */
TieredLock.prototype.show = function () {
	var named = '';
	var first = true;
	for (var k in this._locks) {
		if (this._locks.hasOwnProperty(k)) {
			var n = this._locks[k];
			if (n > 0) {
				if (!first) named += ', ';
				named += k + ' ' + n + 'x';
				first = false;
			}
		}
	}

	console.log('Locks: global ' + this._weight + 'x, named: ' + (first ?  '<none>' : named));
};