Workers API

Support for Workers

For iOS solution please check - NativeScript/ios-jsc#620

Description

General guidelines for the Workers implementation effort and specification in the context of NativeScript.
We have an existing issue here, but the purpose here is to show the road map that the team intends to follow in developing the Workers functionality. The general scenarios we want to support are listed at the bottom.

Limitations

In NativeScript we don’t need to implement all details of the web workers specification, because some of these details are only related to the browser, and won’t have any meaning in the context of a NativeScript application. The features and syntax that will follow has the purpose of describing the adoption of the web workers specification in NativeScript. In this document we will describe and list what we intend to support.

Guidelines from the specification to follow

context

Notice that onmessage and postMessage() need to be hung off the Worker object when used in the main script thread, but not when used in the worker. This is because, inside the worker, the worker is effectively the global scope.

messaging specifics

Data passed between the main thread and workers is copied, not shared. Objects are serialized as they're handed to the worker, and subsequently, deserialized on the other end. The page and worker do not share the same instance, so the end result is that a duplicate is created on each end. Most browsers implement this feature as structured cloning.
The structured cloning algorithm can accept JSON and a few things that JSON can't — like circular references.

messaging transfer ownership

Passing data by transferring ownership (transferable objects): in nativescript we can try to pass native objects by transferring ownership on them.

onerror spec

The error event has the following three fields that are of interest:
message: A human-readable error message.
filename: The name of the script file in which the error occurred.
lineno: The line number of the script file on which the error occurred.

importScripts

ImportScripts in a nativescript context mean require. If we want to support this syntax we need an alias for require.

Syntax

The following example will be the general syntax to use when working with Workers. Syntax is based on web worker specification.

<app_name>/app/main.js

// create new worker
var myWorker = new Worker("worker.js");

// on worker error handler
myWorker.onerror = function (e) {
 //do on worker error
}

// receive messages from worker
myWorker.onmessage = function (e) {
  result.textContent = e.data;
}
....
// send messages to worker
myWorker.postMessage("message will be sent to worker");

//The worker thread is killed immediately without an opportunity to complete its operations or clean up after itself.
myWorker.terminate();

myWorker.onclose = function () {
//on close (clean up)
}

<app_name>/app/worker.js

onmessage = function(e) {
  postMessage(e.data); // worker -> main
}

//worker closes it self
close();

Supported APIs:

Worker Object:

Worker.onerror
Worker.onmessage
Worker.postMessage()
Worker.terminate()

Worker Global Object:

WorkerGlobalObject.self
WorkerGlobalObject.onmessage
WorkerGlobalObject.onerror
WorkerGlobalObject.onclose
WorkerGlobalObject.close()
WorkerGlobalObject.postMessage()
WorkerGlobalObject.importScripts()

Implementation steps:

Also consider researching support for shared array buffers and atomics
as per the spec https://github.com/tc39/ecmascript_sharedmem

This is already under a flag in Chrome 48+

@NathanaelA

@NathanaelA while experimenting with the worker API, I too wished that I could pass just a string, but could not. In the end it all boils down to a string, that is compiled in v8; only one has a source, and the other - doesn't, so it should be possible. Can't say yet if it will be in on the end of the first iteration of the WebWorkers support.

@NathanaelA

@NathanaelA How does one go about experimenting with the preview channel of the WebWorkers?

@roblav96

@roblav96 when they are ready, they will be available in the master branch for others to test and experiment with.
You can normally fetch the latest unstable changes from the master by invoking tns platform add android@next

@Pip3r4o So are you saying I can run tns platform add android@next to experiment with the WebWorkers? :D

@roblav96

@roblav96 as soon as they make it into the master branch, yes. We will let you know when that is.

@Pip3r4o Awesome! Thanks so much!

How might one go about applying for dev branch access? I would really like to become more apart of the community. Hopefully going to nativescript developer day will help with that.

Since this issue is about threads, I guess the following question fits here as well - when using tns-core-modules/connectivity, can we leave its code in "main file" (main thread) or do we have to put it in worker (new thread), for max performance?

@dxshindeo

@dxshindeo I think leaving the calls to the main thread is fairly safe and should not be offloaded to a worker thread. In fact a new thread will likely have a negative impact to the app's available memory if it only deals with the connectivity functionality.

Big thanks for clearing that up!

is there any way to use transferable list as current state? postMessage accepts just 1 argument and throws exception when I provide a transferable list.

last I checked you can only transfer primitives

You can transfer objects recursively, but they can only contain primitives.

Is there any plan to move forward on this? I would love to be able to pass native object.
Also i asked on the module repo but got no answer. Is there a way to combine this with a service? Which means having an Android background service running on its own thread? (bluetooth, udp, tcp ...)

@farfromrefug

@farfromrefug, currently there are some technical limitations which prevent from passing native objects back and forth background workers.

As a workaround you could store your native objects into some java dictionary and only pass the key to the worker thread.

For example you could define a centralized dictionary:

package com.myapp;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public final class WorkersContext {
    private final static Map<String, Object> container = new ConcurrentHashMap<String, Object>();

    public static Object getValue(String key) {
        return container.get(key);
    }

    public static void setValue(String key, Object value) {
        container.put(key, value);
    }
}

which you could use to persist your native object:

var worker = new Worker("./EvalWorker.js");
var nativeObject = new java.io.File("aaa.js");
com.myapp.WorkersContext.setValue("my_key", nativeObject);
var message = {
    value: { key: "my_key" }
};
worker.postMessage(message);

and then in your background worker retrieve the stored native object:

onmessage = function(msg) {
    var key = msg.data.value.key;
    var nativeObject = com.myapp.WorkersContext.getValue(key);
    // ... use the native object here
}

@darind

@darind that's actually a nice idea and easy enough to implement. Would need to find a counterpart for iOS though.
Do you have any idea about the service thing? Right now i do have a service extending android.app.Service And in this i run my bluetooth code. But the fact that any js is run on the main thread makes me really wonder about the real use of my service right now.

Does anyone else have issues using existing code NativeScript/Angular code in the worker?
I always get "Error: The AngularCompilerPlugin was not found. The @ngtools/webpack loader requires the plugin.", and I can't seem to get around it.

Hello, I'm having troubles using the geolocation plugin (nativescript-geolocation) inside a worker. I got the following error:

Error: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference

The error shows when i use the required plugin and execute one of it's functions:

const geolocation = require("nativescript-geolocation");
const { Accuracy } = require("tns-core-modules/ui/enums");
...
async function getLocation() {

await geolocation
    .getCurrentLocation({                           <= here explodes.
        desiredAccuracy: Accuracy.high,
        maximumAge: 5000,
        timeout: 20000
    })
    .then(res => {

...

Is there a way around? or am I doing something wrong?

Thx

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Workers API #532

Support for Workers

Description

Limitations

Guidelines from the specification to follow

Syntax

Supported APIs:

Worker Object:

Worker Global Object:

Implementation steps:

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Workers API #532

Description

Support for Workers

Description

Limitations

Guidelines from the specification to follow

Syntax

Supported APIs:

Worker Object:

Worker Global Object:

Implementation steps:

Activity

NathanaelA commented on Aug 9, 2016

blagoev commented on Aug 12, 2016

NathanaelA commented on Aug 20, 2016

petekanev commented on Aug 20, 2016

roblav96 commented on Aug 30, 2016

petekanev commented on Aug 30, 2016

roblav96 commented on Aug 30, 2016

petekanev commented on Aug 30, 2016

NathanaelA commented on Aug 30, 2016

roblav96 commented on Aug 30, 2016

26 remaining items

dxshindeo commented on Jan 4, 2017

petekanev commented on Jan 4, 2017

dxshindeo commented on Jan 4, 2017

mohammadrafigh commented on May 28, 2018

dxshindeo commented on May 31, 2018

petekanev commented on Jun 8, 2018

farfromrefug commented on Dec 18, 2018

darind commented on Dec 18, 2018

farfromrefug commented on Dec 19, 2018

jerbob92 commented on Jan 10, 2019

es-eph commented on Oct 31, 2019

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