Using Worker for Multithreaded Concurrency in ArkTS

#harmonyos #arkts #multithreading #workerthread

Read the original article：Using Worker for Multithreaded Concurrency in ArkTS

Requirement Description

The Worker class in ArkTS enables creation of background threads with independent execution contexts. These threads operate outside the UI main thread and are ideal for handling long-running or computationally intensive tasks without freezing the UI.

Background Knowledge

Unlike TaskPool, which handles thread lifecycle automatically, the Worker model grants you full control over the lifecycle of a thread. Each Worker runs in its own context, allowing for data isolation, flexible communication, and customizable initialization.

Worker-based concurrency supports:

Independent message event loop
Separate memory context
Custom termination and control

Implementation Steps

Create a new Worker thread using new Worker(path), where path points to an .ets file containing workerMain.
Use postMessage() to send data from main thread to the worker.
Use onmessage to receive messages in both main and worker threads.
Use terminate() to stop the worker manually.

Note: Worker must be created in an .ets file. The target file must define a global function named workerMain().

Code Snippet / Configuration

main.ets

import worker from '@ohos.worker';

@Entry
@Component
struct Index {
  private myWorker: worker.Worker | undefined = undefined;

  aboutToAppear() {
    this.myWorker = new worker.Worker('worker.ts');
    this.myWorker.onmessage = (data: worker.MessageEvent) => {
      console.info('Main thread received message: ' + data.data);
    }
    this.myWorker.postMessage('Hello from Main Thread');
  }

  aboutToDisappear() {
    this.myWorker?.terminate();
  }

  build() {
    Column() {
      Text('Main UI Thread')
    }
  }
}

worker.ets

import worker from '@ohos.worker';

globalThis.workerMain = function () {
  worker.onmessage = function (event: worker.MessageEvent) {
    console.info('Worker received: ' + event.data);
    worker.postMessage('Hello from Worker');
  }
}

Test Results

Successfully sent and received messages between main thread and worker.
Verified that onmessage event handlers work bidirectionally.
Observed that UI remains responsive while background thread operates independently.

Limitations or Considerations

Worker file must be separate .ets file and contain globalThis.workerMain definition.
UI-related operations (e.g. AppStorage, UI rendering) are not accessible in Worker threads.
Worker threads require manual termination using terminate(); they do not auto-scale.
Data passed between threads must be serializable (no complex or cyclic structures).

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