Code that manages queues for River5, for review. See the blog post linked to in the first comment. (Revision to earlier gist.)

codeQueues2.js

function readRiverFile (relpath, afterReadCallback, callback) {
	var f = config.dataFolder + relpath;
	if (riverQueues [f] === undefined) {
		riverQueues [f] = [callback];
		fs.readFile (f, function (err, jsontext) {
			var jstruct = undefined;
			if (!err) {
				try {
					jstruct = JSON.parse (jsontext);
					}
				catch (err) {
					}
				}
			jstruct = afterReadCallback (jstruct);
			var theQueue = riverQueues [f];
			delete riverQueues [f];
			for (var i = 0; i < theQueue.length; i++) {
				theQueue [i] (jstruct);
				}
			});
		}
	else {
		riverQueues [f].push (callback);
		}
	}

Here's the blog post that explains --

http://scripting.com/2018/01/14/155244.html

Dave