worker-task-runner

Run a task inside a web worker

Your app can send to Web Worker a message with a script URL and data. Worker will execute the task and return the result back.

Worker uses StealJS module loader to asynchronously load the task module. Data is sent via postMessage.

The package also provides helpers for sending SharedArrayBuffer to the worker task runner. See demo demo/shared-array-task/demo.js for an example.

API

Message format

• type message type, values are defined in src/constants.js:
  • from Worker: ready, task-result
  • to Worker: run-task
• taskUrl {String} represents a URL to a task file that Worker will load and execute.
• taskData {Any} data to sent to Worker to pass to the given task.
• result {Any} contains data that worker produced as a result of executing the given task.

Helpers

• Main:
  • create - creates a worker, returns a Task that will be resolved when the worker sends the READY event.
  • runTask - runs a task in a worker. Expects: a worker instance and a URL of a task module that will be run in the worker.
• Utils:
  • execTask - forks a task and prints out how much time it took to execute it.
• SharedArrayBuffer:
  • createBuffer
  • bufferToArray

Example:

worker.postMessage({
  type: "run-task",
  taskUrl: "src/my-task.js",
  taskData: [1,2,3]
})
 
worker.onmessage = ev => {
  if (ev.data.type === 'ready') {
    console.log('Worker is ready!')
  }
  if (ev.data.type === 'task-result') {
    console.log('Worker finished task:', ev.data.result)
  }
}

Example:

Low-level

You can use Worker directly and just use the message API

const worker = new Worker("worker-task-runner/src/worker.js")
const taskUrl = "demo/task.js"
const data = [1, 2, 3, 4]
 
const myCallback = result => console.log("Web worker finished: ", result)
 
worker.onmessage = ev => {
  if (ev.data === "ready") {
    // Send a task script URL to worker along with data. Note: type has to be `run-task`
    worker.postMessage({
      type: "run-task",
      taskUrl,
      taskData
    })
  }
  if (ev.data && ev.data.type === "task-result"){
    myCallback(ev.data.result)
  }
}

Functional-style with Tasks

You can use the following helpers to work in a functiona style using data.task's Task:

// Import helpers:
const { create, runTask, execTask } = require('worker-task-runner')
 
// Define your task URL and data:
const workerUrl = "worker-task-runner/src/worker.js"
const taskUrl = "demo/task.js"
const data = [1, 2, 3, 4]
 
// Define your main app that creates a worker and runs a task:
const app =
  create(workerUrl)
  .chain(worker => runTask(worker, taskUrl)(data))
 
// Execute the application (see `data.task`):
app.fork(err => console.log("Error: ", error),
         res => console.log("Result: ", res))
 

Or if you prefer a Promise:

// TODO :)

SharedArrayBuffer

Main app may look like this:

const { create, runTask, createBuffer, bufferToArray } = require('worker-task-runner')
const execTask = require('worker-task-runner/src/utils/exec')
 
// Create shared array buffer to send to worker:
const data = { buffer: createBuffer(50, 'Int32Array'), type: 'Int32Array'}
 
// Define the main app: create a worker and run a task:
const app =
  create('src/worker')
  .chain(worker => runTask(worker, 'demo/shared-array-task/task')(data))
  .map(bufferToArray)
 
// Execute the application (see `data.task`):
execTask(app)

The worker task may look like:

const Task = require('data.task')
const { bufferToArray } = require('worker-task-runner')
 
// testTask :: a -> Task b
const testTask = ({ buffer, type }) =>
  new Task((reject, resolve) => {
 
    // Convert the buffer array to a typed array:
    let array = bufferToArray({ buffer, type })
 
    // Do some actions that will update the buffer array:
    array.forEach((a, i) => array[i] = i * 3)
 
    // Resolve the task:
    resolve({ buffer, type })
  })
 
module.exports = testTask
 

Release Notes

• 0.0.2 Helpers and demo for using SharedArrayBuffer. Also define the helpers module to be package's main script.
  • createBuffer
  • bufferToArray
• 0.0.1 Initial version:
  • Send data via postMessage.
  • Worker loads the given task script using StealJS module loader.
  • Helpers for using data.task Task.