like a Thread pool in nodejs

parallel_process.js

"use strict";
var P = require("bluebird")
var _ = require("underscore")

let items = [0,12.5,5,5,87,8,7,48,58,7,78,4,87,854,84,787,78,4,87,7]
console.log("items length ------------> " + items.length)

let level = 0

function processList(_items){
	level++
	console.log("level ------------> " + level)
	console.log(_items)

	let selecteds = [] 

	for(var counter=0;counter < 3; counter++)
	{
		if(_items.length > 0){
			selecteds.push(anyAsyncMethod(_items.pop()))
		}
	}

	console.log("promisses count -> " + selecteds.length)
	P.all(selecteds)
	.then( results => {

		if(_items.length > 0){
			processList(_items)
		}else{
			console.log("---------> END")
			process.exit(0)
		}
	})
}

processList(items)


function anyAsyncMethod(number){

    let rand = Math.round(Math.random() * (3000 - 500)) + 500;
	let p = new Promise(function(resolve){ 
		
		setTimeout(function(){
		 console.log("resolving " + number)
		 resolve(number)
	    }, rand)

	}); 
	return p
}