single-concurrent/index.js

"use strict";

const capturePromise = require("capture-promise");
const debug = require("debug")("single-concurrent");

const { validateArguments } = require("@validatem/core");
const isFunction = require("@validatem/is-function");
const required = require("@validatem/required");

module.exports = function singleConcurrent(_func) {
	let [ func ] = validateArguments(arguments, {
		func: [ required, isFunction ]
	});

	let running = false;

	return async function (... args) {
		if (running === false) {
			debug(`starting`);
			running = true;

			try {
				return await capturePromise(() => func(... args));
			} finally {
				// Yes, this gets called *even if* the above successfully returns, before the resulting Promise is resolved.
				debug(`completed`);
				running = false;
			}
		} else {
			debug(`already running; skipping`);
		}
	};
};