queue.js

"use strict";

const Queue = module.exports = function () {
    this.queue      = []
    this.awaiting   = []
}

Queue.prototype = {
    take: function () {
        let queue = this.queue,
            awaiting = this.awaiting
    
        return function (cb) {
            if (queue.length === 0) {
                // no items in queue so wait
                awaiting.push(cb)
            } else {
                let item = queue.shift()
                cb(null, item)    
            }
        }
    },
    
    poll: function () {
        return this.queue.shift()        
    },
    
    put: function (item) {
        if (this.awaiting.length > 0) {
            let cb = this.awaiting.shift()
            cb(null, item)
        } else {
            this.queue.push(item)
        }
        
    },
    
    size: function () {
        return this.queue.length        
    }
}