Canceling Tasks in Multithreading with TaskPool

Task objects of the TaskPool cannot be passed across threads. Therefore, tasks cannot be canceled directly from child threads. Starting from API version 18, tasks have been enhanced with the task ID, allowing tasks to be canceled in child threads using this ID. You can store the task ID of a created task in a Sendable object and use this object to cancel the task from a child thread. For details, see the following example.

1. Define a Sendable class and store the task ID in the class properties.

   // sendable.ets
   @Sendable
   export class SendableTest {
     // Store the task ID.
     private taskId: number = 0;
   
     constructor(id: number) {
       this.taskId = id;
     }
   
     public getTaskId(): number {
       return this.taskId;
     }
   }
   

   Sendable.ets

2. Submit a delayed task to the TaskPool from the UI main thread and cancel it from a child thread.

   // TaskpoolCancel.ets
   import { taskpool } from '@kit.ArkTS';
   import { SendableTest } from '../utils/Sendable';
   import { BusinessError } from '@kit.BasicServicesKit';
   import { PromptAction } from '@kit.ArkUI';
   
   @Concurrent
   function cancel(send: SendableTest) {
     // Cancel the task in the child thread based on the task ID.
     taskpool.cancel(send.getTaskId());
     console.info('cancel task finished');
   }
   
   @Concurrent
   function delayed() {
     console.info('delayed task finished');
   }
   
   @Entry
   @Component
   struct TaskpoolCancel {
     @State message: string = 'CancelTaskpool';
     @State returnMessage: string = 'return...';
     @State promptAction: PromptAction = this.getUIContext().getPromptAction();
   
     build() {
       Row() {
         Column() {
           Button(this.message)
             .fontSize(25)
             .fontWeight(FontWeight.Bold)
             .onClick(async () => {
               let task = new taskpool.Task(delayed);
               taskpool.executeDelayed(2000, task).catch((e: BusinessError) => {
                 console.error(`taskpool execute error, message is: ${e.message}`);
                 // taskpool execute error, message is: taskpool:: task has been canceled.
               });
               let send = new SendableTest(task.taskId);
               taskpool.execute(cancel, send);
               this.returnMessage = 'Taskpool canceled!';
               this.promptAction.showToast({ message: this.returnMessage });
             })
           // ...
         }
         .width('100%')
       }
       .height('100%')
     }
   }
   

   TaskpoolCancel.ets