Threadify

Threadify is a browser-side Javascript library that allows you to run any Javascript function into a web worker.

Example of a threadified function:

var myFunction = threadify(function (param1, param2) {
    // This will be executed inside a web worker
    console.log("Hello from the worker");
    return param1 + param2;
});

var job = myFunction("foo", "bar");

job.done = function (result) {
    console.log(result);
};

Getting Started

Getting Threadify

Standalone Version

First download the Threadify zip or clone the repository.

Then include the threadify.js or threadify.min.js (from the dist folder) in you HTML page:

<script src="dist/threadify.js"></script>

NPM and Browserify

First install the threadify package:

npm install --save threadify

Then include it where you need it:

var threadify = require("threadify");

Threadifying a Function

To run a function in a web worker, you have to threadify it:

var myFunction = threadify(function (param1, param2) {
    // The code of this function will be executed inside a web worker
    return param1 + param2;
});

Then, to run your threadified function, you just have to call it as any other function:

var job = myFunction("param1", "param2");

When you call your threadified function, it returns a Job object that allow you to control the worker and to retrieve values returned by the function.

To get the result of your function, just define a done callback on the Job object:

// this function will be called once the function return something.
job.done = function (result) {
    console.log(result);
};

Returning Values

The simplest way to return a value from the threadified function is to use the return keyword as usual:

var myFunction = threadify(function (param1, param2) {
    return param1 + param2;
});

But if you have asynchrone code in your function (or if you want to return more than one value), you will not be able to use the return keyword. But you can use the this.return() method instead:

var myFunction = threadify(function (param1, param2) {
    this.return(param1, param2);
});

Be careful of the this context when you call this.return() from a callback. For instance, the following code will not work because of the wrong this context:

var myFunction = threadify(function (param1, param2) {
    setTimeout(function () {
        this.return(param1, param2);
    }, 1000);
});

To fix it, you can modify it like this:

var myFunction = threadify(function (param1, param2) {
    var thread = this;
    setTimeout(function () {
        thread.return(param1, param2);
    }, 1000);
});

The worker still alive until you return something or you terminate it explicitly.

NOTE: if you just use the return keyword without any value, the worker will not be terminated.

About Web Workers Limitations

Web workers are executed in an other thread than your main script / page, this causes some limitations detailed bellow.

Accessible Objects

From the worker (the threadified function) you cannot access to all browser's objects you are used to. For instance, this is some objects that are not accessible:

• the window object,

• the document object ,

• DOM / DOM elements (you cannot manipulate the HTML of your page),

• other functions / classes / objects / variables of your main thread (you cannot access to anything outside your threadified function),

• ...

Arguements and Returned Values

You cannot send / return any type of argument to / from a worker. Threadify allows you to send / return:

• Simple types / values (copied):

  • Number
  • String
  • Boolean
  • Array¹
  • Object¹
  • undefined
  • null
  • Infinity
  • NaN

• Blob, File (copied) TODO: check if File works

• Error objects (copied)

• ArrayBuffer (transfered)

• Typed arrays (transfered):

  • Int8Array
  • Uint8Array
  • Uint8ClampedArray
  • Int16Array
  • Uint16Array
  • Int32Array
  • Uint32Array
  • Float32Array
  • Float64Array

• DataView (transfered)

• Canvas ImageData (transfered)

Depending on their types, arguments can be copied or transfered to the worker. A transfered argument means that its access is transfered to the worker and that it will no more be accessible from the main thread.

NOTE¹: Only if they contains allowed types (no class, no function,...)

Job API

You get the Job object each time you call a threadified function:

var myFunction = threadify(function (param1, param2) {
    // The code of this function will be executed inside a web worker
    return param1 + param2;
});

var job = myFunction("foo", "bar");

Methods

• job.terminate(): terminates immediately the worker without letting it an opportunity to finish its operations.

job.terminate();

Callbacks

• job.done = function (result) {}: called when the threadified function returns something. Please note that the worker is terminated right after it returns the value.

• job.failed = function (error) {}: called when an error occurred in the threadified function. Please note that the worker is not always terminated when an error occurred.

• job.terminated = function () {}: called when the worker is terminated.

Thread API

Inside the threadified function, you have access to a Thread object through the this context.

var myFunction = threadify(function (param1, param2) {
    var thread = this;
});

Methods

• thread.terminate(): terminates immediately the worker.

• thread.error(error): Reports an error (this will calls the job.failed callback function). Please not that calling this method will not terminate the worker.

• thread.return(param [, param2 [, ...]]): return one or more values (this will call the job.done callback function) and terminates the worker.

Hacking

Threadify is built using Grunt and Browserify. To start hacking Threadify, you will have to install few tools.

Installing Dependencies

To build Threadify, you will first have to install Node.js (or io.js).

NOTE: If you are on Ubuntu / Debian Linux you must install the nodejs-legacy package.

Next, install globally the grunt-cli npm package:

npm install -g grunt-cli

Then install the required dependencies:

npm install

Building Threadify

Once the build stuff and dependencies installed, you just have to run the grunt command to build Threadify:

grunt

All generated files are in the dist folder.

Coding Style

Threadify follows the Yandex Javascript CodeStyle EXCEPT for the quote marks where double quotes (") are used.

You can automatically check that your code follows the conventions by using this command:

grunt jscs

Running Tests

To run the tests, first check that the javascript is well formed and that it follows the coding style:

grunt jshint jscs

Then, open the following page in your web browser:

• test/SpecRunner.html

Changelog

• 0.2.1: Fix for old browsers that do not implement ImageData
• 0.2.0: Allow to tranfer / copy more types between the main thread and the worker
• 0.1.0: First release: basic functionalities required to build and run workers