tilestrata-mapnik/tilelive-mapnik/lib/lockingcache.js

A TileStrata plugin for rendering tiles with mapnik

module.exports = LockingCache;
function LockingCache(generate, timeout) {
	this.callbacks = {};
	this.timeouts = {};
	this.results = {};

	// When there's no generator function, you
	this.generate = generate || function() {};

	// Timeout cached objects after 1 minute by default.
	// A value of 0 will cause it to not cache at all beyond, just return the result to
	// all locked requests.
	this.timeout = (typeof timeout === "undefined") ? 60000 : timeout;
}

LockingCache.prototype.get = function(id, callback) {
	if (!this.callbacks[id]) this.callbacks[id] = [];
	this.callbacks[id].push(callback);

	if (this.results[id]) {
		this.trigger(id);
	} else {
		var ids = this.generate.call(this, id);
		if (!ids || ids.indexOf(id) < 0) {
			this.put(id, new Error("Generator didn't generate this item"));
		} else ids.forEach(function(id) {
			this.results[id] = this.results[id] || true;
		}, this);
	}
};

LockingCache.prototype.del = function(id) {
	delete this.results[id];
	delete this.callbacks[id];
	if (this.timeouts[id]) {
		clearTimeout(this.timeouts[id]);
		delete this.timeouts[id];
	}
};

LockingCache.prototype.put = function(id) {
	if (this.timeout > 0) {
		this.timeouts[id] = setTimeout(this.del.bind(this, id), this.timeout);
	}
	this.results[id] = Array.prototype.slice.call(arguments, 1);
	if (this.callbacks[id] && this.callbacks[id].length) {
		this.trigger(id);
	}
};

LockingCache.prototype.clear = function() {
	for (var id in this.timeouts) {
		this.del(id);
	}
};

LockingCache.prototype.trigger = function(id) {
	if (this.results[id] && this.results[id] !== true) {
		process.nextTick(function() {
			var data = this.results[id];
			var callbacks = this.callbacks[id] || [];

			if (this.timeout === 0) {
				// instant purge with the first put() for a key
				// clears timeouts and results
				this.del(id);
			} else {
				delete this.callbacks[id];
			}

			callbacks.forEach(function(callback) {
				callback.apply(callback, data);
			});
		}.bind(this));
	}
};