Code that manages queues for River5, for review. See the blog post linked to in the first comment.

codeQueues.js

function readRiverFile (relpath, callback) {
	var f = config.dataFolder + relpath;
	if (riverQueues [f] === undefined) {
		riverQueues [f] = [callback];
		fs.readFile (f, function (err, data) {
			if (err) {
				console.log ("readRiverFile: err.message == " + err.message);
				}
			else {
				var theQueue = riverQueues [f];
				delete riverQueues [f];
				for (var i = 0; i < theQueue.length; i++) {
					theQueue [i] (data);
					}
				}
			});
		}
	else {
		riverQueues [f].push (callback);
		}
	}

Here's the blog post with the background --

http://scripting.com/2018/01/13/183433.html

Dave