bugcore/lib/concurrent/Lock.js

bugcore is a JavaScript library that provides a foundational architecture for object oriented JS

/*
 * Copyright (c) 2016 airbug Inc. http://airbug.com
 *
 * bugcore may be freely distributed under the MIT license.
 */


//-------------------------------------------------------------------------------
// Annotations
//-------------------------------------------------------------------------------

//@Export('Lock')

//@Require('Class')
//@Require('Event')
//@Require('EventDispatcher')
//@Require('Queue')
//@Require('Tracer')


//-------------------------------------------------------------------------------
// Context
//-------------------------------------------------------------------------------

require('bugpack').context("*", function(bugpack) {

    //-------------------------------------------------------------------------------
    // BugPack
    //-------------------------------------------------------------------------------

    var Class               = bugpack.require('Class');
    var Event               = bugpack.require('Event');
    var EventDispatcher     = bugpack.require('EventDispatcher');
    var Queue               = bugpack.require('Queue');
    var Tracer              = bugpack.require('Tracer');


    //-------------------------------------------------------------------------------
    // Simplify References
    //-------------------------------------------------------------------------------

    var $trace              = Tracer.$trace;


    //-------------------------------------------------------------------------------
    // Declare Class
    //-------------------------------------------------------------------------------

    /**
     * @class
     * @extends {EventDispatcher}
     */
    var Lock = Class.extend(EventDispatcher, {

        _name: "Lock",


        //-------------------------------------------------------------------------------
        // Constructor
        //-------------------------------------------------------------------------------

        /**
         * @constructs
         */
        _constructor: function() {

            this._super();


            //-------------------------------------------------------------------------------
            // Private Properties
            //-------------------------------------------------------------------------------

            /**
             * @private
             * @type {Queue.<function()>}
             */
            this.acquisitionQueue = new Queue();

            /**
             * @private
             * @type {boolean}
             */
            this.locked = false;
        },


        //-------------------------------------------------------------------------------
        // Public Methods
        //-------------------------------------------------------------------------------

        /**
         * @return {boolean}
         */
        hasWaiters: function() {
            return this.acquisitionQueue.getCount() > 0;
        },

        /**
         * @return {boolean}
         */
        isLocked: function() {
            return this.locked;
        },

        /**
         * @return {boolean}
         */
        tryLock: function() {
            if (this.isLocked()) {
                return false;
            } else {
                this.acquireLock();
                return true;
            }
        },

        /**
         *
         */
        unlock: function() {
            this.releaseLock();
        },

        /**
         * @param {function(*=)=} method
         */
        waitLock: function(method) {
            this.queueAcquisition(method);
            this.processQueue();
        },


        //-------------------------------------------------------------------------------
        // Private Methods
        //-------------------------------------------------------------------------------

        /**
         * @private
         * @param {function(*=)=} method
         */
        acquireLock: function(method) {
            this.locked = true;
            if (method) {
                method();
            }
        },

        /**
         * @private
         */
        processQueue: function() {
            if (!this.isLocked()) {
                if (this.acquisitionQueue.getCount() > 0) {
                    var nextMethod = this.acquisitionQueue.dequeue();
                    this.acquireLock(nextMethod);
                } else {
                    this.dispatchEvent(new Event(Lock.EventTypes.EMPTY));
                }
            }
        },

        /**
         * @private
         * @param {function()} method
         */
        queueAcquisition: function(method) {
            this.acquisitionQueue.enqueue(method);
        },

        /**
         * @private
         */
        releaseLock: function() {
            this.locked = false;
            this.dispatchEvent(new Event(Lock.EventTypes.RELEASED));
            var _this = this;

            // NOTE BRN: We use a setTimeout here to help prevent stack overflows when it comes to the processing of the
            // queue.

            setTimeout($trace(function() {
                _this.processQueue();
            }), 0);
        }
    });


    //-------------------------------------------------------------------------------
    // Static Properties
    //-------------------------------------------------------------------------------

    /**
     * @static
     * @enum {string}
     */
    Lock.EventTypes = {
        EMPTY: "Lock:Empty",
        RELEASED: "Lock:Released"
    };


    //-------------------------------------------------------------------------------
    // Exports
    //-------------------------------------------------------------------------------

    bugpack.export('Lock', Lock);
});