Threaded class

Fork instances of classes (while keeping typings) with one line of code.

Getting started

Let's say you have a class that has several computational-heavy methods:

// Normal, single-threaded way:
import { Professor } from './professor'

function getStory() {
  let mrSmith = new Professor('maths', 'greek')
  let story = mrSmith.talkAboutAncientGreece() // takes a loong time
  return story
}

This library helps you create an asynchronous version of the instance of that class. The instance will have almost the same API as the original (all methods return promises instead), but will run in a separate thread.

// Multi-threaded, asynchronous way:
import { threadedClass} from 'threadedclass'
import { Professor } from './professor'

async function getStory() {
  let mrSmith = await threadedClass<Professor>('./professor.js', Professor, ['maths', 'greek'])
  let story = await mrSmith.talkAboutAncientGreece() // still takes a loong time, but now runs in a separate thread
  return story
}

The instance returned by makeThreaded() has methods equivalent to the original, but all properties will be asynchronous (Promises).

API

API reference

NodeJS: Typescript example

import { threadedClass} from  'threadedclass'
import { Professor } from './professor'

threadedClass<Professor>(
    './professor.js',     // Path to imported module (this should be the same path as is in require('XX') or import {class} from 'XX'} )
    Professor ,        // The class to be forked
    ['maths', 'greek'], // Array of arguments to be fed into the class constructor
    {} // Config (see below)
)
.then((instance) => {
    return mrSmith.talkAboutAncientGreece() // All methods returns a Promise
})
.then((story) => {
    console.log(story)
})

NodeJS: Javascript example

var threadedClass = require('threadedclass').threadedClass
var Professor = require('./professor')

threadedClass('./professor.js', Professor, ['maths', 'greek'])
.then((instance) => {
    return mrSmith.talkAboutAncientGreece() // All methods returns a Promise
})
.then((story) => {
    console.log(story)
})

Browser: Javascript example

Example

<script type="text/javascript" src="lib/threadedClass.js"></script>
<script type="text/javascript" src="professor.js"></script>
<script type="text/javascript">
    var threadedClass = ThreadedClass.threadedClass

    threadedClass('../professor.js', Professor, ['maths', 'greek'], { // path to module is relative to threadedClass.js
        pathToWorker: 'lib/threadedclass-worker.js' // in browser, a path to the worker-scrip must also be provided
    })
    .then((instance) => {
    return mrSmith.talkAboutAncientGreece() // All methods returns a Promise
    })
    .then((story) => {
        console.log(story)
    })
</script>

Options

An optional options object can be passed to threadedClass() with the following properties:

• threadUsage Optional number
  A number between 0 - 1, how large part of a thread the instance takes up. For example; if set to 0.1, a thread will be re-used for up to 10 instances.
• threadId Optional string
  Set to an arbitrary id to put the instance in a specific thread. Instances with the same threadIds will be put in the same thread.
• disableMultithreading Optional boolean
  Set to true to disable multi-threading, this might be useful when you want to disable multi-threading but keep the interface unchanged.
• Not implemented yet: autoRestart Optional boolean
  Set to true to automatically restart a crashed thread. ThreadedClassManager will emit the "restarted" event upon restart.

Features

Supported imports

• Classes imported from your own modules. import { MyClass } from './myModule'
• Classes imported from external dependencies. import { DatClass } from 'dat-library'
• Classes importted from native Node modules. import { StringDecoder } from 'string_decoder'

Supported methods, arguments / parameters & return values

When calling a method of your threaded instance (threaded.myMethod()), there are some limitations to what data-types are allowed to be provided and returned.

Supported data types

• All JSON-serializable types; numbers, strings, arrays, objects etc..
• Buffers
• Functions (such as callbacks or returned functions)

Unsupported data types

• Non-JSON-encodable types, such as objects with cyclic references.
• Instances of classes (the instance will be serialized as JSON and piped through, but its methods will not).

Known limitations

• The to-be-threaded class must not be referencing any global variables, as the class is run in its own sandbox.
• No garbage-collection of callback-functions
  Currently, if you give a callback to a method (like so: threaded.myMethod(() => {})) a reference to the method will be stored indefinitely, because we cannot determine if the reference is valid in the child process.
• There is a noticable delay when spawning a new thread, and since each thread is its own Node-process it uses up a few Megabytes of memory. If you intend to spawn many instances of a class, consider using the threadUsage option (for example threadUsage: 0.1 will put 10 instances in a thread before spawning a new).

Todo

• Support for NodeJS Worker-threads (added as experimental in version 11)