Synchronous Task Development (TaskPool and Worker)

Synchronous tasks are executed in order among multiple threads. Synchronization primitives, such as locks, are used by these tasks for coordination between each other.

To implement synchronous tasks, you must consider the collaboration and synchronization between multiple threads and ensure the correctness of data and program execution.

If synchronous tasks are independent of each other, you are advised to use TaskPool, which focuses on single independent tasks. For example, a series of imported static methods or methods implemented in singletons are independent. If synchronous tasks are associated with each other, use Worker, for example, methods implemented in class objects (not singleton class objects).

Using TaskPool to Process Independent Synchronous Tasks

TaskPool is recommended for scheduling independent tasks. Typical independent tasks are those using static methods. If a unique handle or class object constructed using a singleton points to multiple tasks and these tasks can be used between different worker threads, you can also use TaskPool.

1. Define a concurrency function that internally calls the synchronous methods.

2. Create a task, call execute() to execute the task, and perform operations on the result returned by the task.

3. Perform concurrent operations.

Simulate a singleton class that contains synchronous calls.

// handle.ts code
export default class Handle {
  static getInstance(): void {
    // Return a singleton object.
  }

  static syncGet(): void {
    // Synchronous getter.
  }

  static syncSet(num: number): number {
    // Simulate synchronization step 1.
    console.info("taskpool: this is 1st print!");
    // Simulate synchronization step 2.
    console.info("taskpool: this is 2nd print!");
    return num++;
  }
}

Use TaskPool to call the related synchronous methods.

// Index.ets code
import taskpool from '@ohos.taskpool';
import Handle from './Handle'; // Return a static handle.

// Step 1: Define a concurrency function that internally calls the synchronous methods.
@Concurrent
function func(num: number): boolean {
  // Call the synchronous wait implemented in a static class object.
  Handle.syncSet(num);
  return true;
}

// Step 2: Create and execute a task.
async function asyncGet(): Promise<void> {
  // Create a task and pass in the function func.
  let task: taskpool.Task = new taskpool.Task(func, 1);
  // Execute the task.
  let res: boolean = await taskpool.execute(task) as boolean;
  // Print the task result.
  console.info("taskpool: task res is: " + res);
}

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';

  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            // Step 3: Perform concurrent operations.
            asyncGet();
          })
      }
      .width('100%')
      .height('100%')
    }
  }
}

Using Worker to Process Associated Synchronous Tasks

Use Worker when you want to schedule a series of synchronous tasks using the same handle or depending on the same class object.

1. Create a Worker object in the main thread and receive messages from the worker thread.

   import worker from '@ohos.worker';
   
   @Entry
   @Component
   struct Index {
     @State message: string = 'Hello World';
   
     build() {
       Row() {
         Column() {
           Text(this.message)
             .fontSize(50)
             .fontWeight(FontWeight.Bold)
             .onClick(() => {
               let w: worker.ThreadWorker = new worker.ThreadWorker('entry/ets/workers/MyWorker.ts');
               w.onmessage = (): void => {
                 // Receive the result of the worker thread.
               }
               w.onerror = (): void => {
                 // Receive error information of the worker thread.
               }
               // Send a Set message to the worker thread.
               w.postMessage({'type': 0, 'data': 'data'})
               // Send a Get message to the worker thread.
               w.postMessage({'type': 1})
               // ...
               // Select a time to destroy the thread based on the actual situation.
               w.terminate()
             })
         }
         .width('100%')
       }
       .height('100%')
     }
   }
   

2. Bind the Worker object in the worker thread and process the synchronous task logic.

   // handle.ts code
   export default class Handle {
     syncGet() {
       return;
     }
   
     syncSet(num: number) {
       return;
     }
   }
   

   // MyWorker.ts code
   import worker, { ThreadWorkerGlobalScope, MessageEvents } from '@ohos.worker';
   import Handle from './handle'  // Return a handle.
   
   let workerPort : ThreadWorkerGlobalScope = worker.workerPort;
   
   // Handle that cannot be transferred. All operations depend on this handle.
   let handler: Handle = new Handle()
   
   // onmessage() logic of the worker thread.
   workerPort.onmessage = (e : MessageEvents): void => {
    switch (e.data.type as number) {
     case 0:
      handler.syncSet(e.data.data);
      workerPort.postMessage('success set');
     case 1:
      handler.syncGet();
      workerPort.postMessage('success get');
    }
   }