Object Pool - Object pool library for Node.js and the browser

The Object Pool mechanism allows you to consume object from a given pool of objects instead of creating and disposing them. The main use case for the object pool is to reduce the footprint of garbage collection for memory consuming applications. The main usage is probably for games where objects are created and destroyed very quickly especially when dealing with particles.

Installation

For Node.js

npm install objectpool

For the browser you can install via Bower

bower install objectpool

or by copying object-pool.min.js

Documentation

This readme file contains basic usage examples and details on the full API, including methods, attributes and events.

Object Pool

Object Pool is a static object which allows you to create object pool generators. The generators are used to retrieve and release an object.

Accessing the Object Pool Object

In Node.js

var op = require('objectpool');

In the browser

 <script src="/path/to/object-pool/object-pool.min.js"></script>

var op = window.ObjectPool;

Note that you can delete the ObjectPool property from the window object once you copy it locally;

Basic usage

You create a generator by calling the generate(object, [options]) function. There are two types of generators, a constructor generator which creates new items using a constructor function

  var generator = op.generate(function () { this.x = 0; this.y = 0; }); //This generator will generate objects with x and y properties

and a clone generator which generates new items by cloning the provided item:

  var generator = op.generate( {x = 0, y = 0}); //This generator will generate objects with x and y properties

Options

When creating a generator you may supply an options object that has the following properties

Options#count

The number of object to instantiate when the generator is created.

 function Point() {
    this.x = 0;
    this.y = 0;
  }

  var generator = op.generate(Point, { count: 10});
  //Generator contains 10 points created using the Point constructor function

Options#init

A function that will be called for any object retrieved by this generator. The functions receives the returned object as this so you can simply reuse the constructor.

 function Point() {
    this.x = 0;
    this.y = 0;
  }

  function initPoint(x, y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point, { count: 10, init: initPoint });
  var point = generator.get(1,2); //returns a point with x = 1 and y = 2

Options#clear

A function that will be called for every object released back into the pool of this generator.

  function Point() {
    this.x = 0;
    this.y = 0;
  }

  function initPoint(x, y) {
    this.x = x;
    this.y = y;
  }

  function destructor() {
    this.x = 0;
    this.y = 0;
  }

  var generator = op.generate(Point, { count: 10, init: initPoint, clear:destructor });
  var point = generator.get(1,2);
  generator.release(point); //
  console.log(point.x,point.y) // 00

Options#regenerate

A number or a function returning a number which indicates how many objects the generator should create if you try to retrieve an object but there are no objects left in the pool. If this property is unspecified then no new objects are created.

  var generator = op.generate({}, { regenerate: 1 });
  var item = generator.get(); //item == {}

  var generator = op.generate({});
  var item = generator.get(); //item == null

Options#data

An array of objects to be initially added to the pool. If the length of the array less than the value of count option then more objects are generated until the generator contains count objects. If the length of the array is greater than count then count is ignored. The objects from the array are copied by reference to the generator pool.

  var generator = op.generate({}, { data: [1, 2, 3], count: 5 });
  console.log(generator.count()); //5
  console.log(generator.get()); //1

Options#clone

For item generators only A function that will be called to instantiate a new object within the generator pool. If unspecified then the default shallow clone will be used.

  function clone(point) {
    return { x: point.x, y: point.y };
  }

  function initPoint(x, y) {
    this.x = x;
    this.y = y;
  }

  function destructor() {
    this.x = 0;
    this.y = 0;
  }

  var generator = op.generate({ x: 0, y: 0 }, { count: 10, init: initPoint, clear: destructor, clone:clone });

Object Pool Generator

The generator holds the pool of objects and allows you to get an object from the pool or release an object into the pool.

Basic Usage

  function Point(x,y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point, { count: 100, init: Point }); // Creates a pool of 100 points
  var point = generator.get(0,0); // retrieves a point from the pool
  
  ... Do stuff with point ...
  
  generator.release(point); //returns the point to the pool
  

Generator#get([params])

Retrieves an object from the pool. The pool has no reference to the object therefore if the application doesn't reference the returned object it is eligible for garbage collection. If the init function was specified in the generator options, it will be applied to the returned object with the arguments provided to the get function. If the pool is empty (i.e. contains 0 objects) and regenerate was not provided in the generator options null is returned.

  function Point(x,y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point, { count: 100, init: Point }); // Creates a pool of 100 points
  var point = generator.get(0,0); // retrieves a point from the pool

Generator#release(object)

Releases an object into the generator object pool. if clear function was supplied in the generator options it will be applied on the released object passing this as the released object to the function. There is no restriction on the released object (i.e. it can be an object that was not retrieved by the generator). Once the object is released into the generator pool it is referenced by the pool and is not eligible for garbage collection. You may still use the object after it is released to the generator pool, the object within the pool is affected.

  function Point(x,y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point); 
  var point = new Point(1,2); 
  generator.release(point); //returns the point to the pool
  console.log(generator.count()); // 1

Generator#delete(n)

Deletes objects from the generator pool. If n>=1, deletes at most n objects from the generator pool. if n<1, deletes count*n objects from the pool. The objects are completely removed from the pool and are eligible for garbage collection.

  function Point(x,y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point, { count: 105 }); // Creates a pool of 105 points

  generator.delete(5);
  console.log(generator.count()); // 100
  generator.delete(0.5); 
  console.log(generator.count()); // 50

Generator#create(n)

Creates n objects and releases them into the pool. The creation method is the one appropriate for the generator (constructor or cloning) and uses the constructor function or the clone method provided when the generator was created.

  function Point(x,y) {
    this.x = x;
    this.y = y;
  }

  var generator = op.generate(Point); // Creates an empty pool
  generator.create(10);
  console.log(generator.count()); // 10

Generator#count

A function that returns the number of objects in the generator pool

 function Point(x,y) {
   this.x = x;
   this.y = y;
 }

 var generator = op.generate({}, { count: 3 }); 
 console.log(generator.count()); // 3

Generating Arrays

The Object Pool Object comes with a build in array generator.

var arr = op.array.get(); // returns []

This is a preconfigured clone based generator that has nothing special about it. It is there for your convenience.

Tests and Examples

The tests are using the mocha farmework. To run the tests do npm test

There is a particle example using object pools for the browser in the example directory (see example.html). You can run it directly from the browser. The example was written by Jarrod Overson (@jsoverson), the original sources are (here)[http://html5hub.com/build-a-javascript-particle-system].

Legal Mumbo Jumbo (MIT License)

Copyright (c) 2013 Boris Kozorovitzky,

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.