taskpool任务执行结束后如何执行回调方法

import taskpool from '@ohos.taskpool'; 
 
@Concurrent 
function imageProcessing(dataSlice: ArrayBuffer) { 
  // 步骤1: 具体的图像处理操作及其他耗时操作 
  return dataSlice; 
} 
 
function histogramStatistic(pixelBuffer: ArrayBuffer) { 
  // 步骤2: 分成三段并发调度 
  let number = pixelBuffer.byteLength / 3; 
  let buffer1 = pixelBuffer.slice(0, number); 
  let buffer2 = pixelBuffer.slice(number, number * 2); 
  let buffer3 = pixelBuffer.slice(number * 2); 
  let task1 = new taskpool.Task(imageProcessing, buffer1); 
  let task2 = new taskpool.Task(imageProcessing, buffer2); 
  let task3 = new taskpool.Task(imageProcessing, buffer3); 
  taskpool.execute(task1).then((ret: ArrayBuffer[]) => { 
    // 步骤3: 结果处理 
  }); 
  taskpool.execute(task2).then((ret: ArrayBuffer[]) => { 
    // 步骤3: 结果处理 
  }); 
  taskpool.execute(task3).then((ret: ArrayBuffer[]) => { 
    // 步骤3: 结果处理 
  }); 
} 
 
@Entry 
@Component 
struct Index { 
  @State message: string = 'Hello World' 
  build() { 
    Row() { 
      Column() { 
        Text(this.message) 
          .fontSize(50) 
          .fontWeight(FontWeight.Bold) 
          .onClick(() => { 
            let data: ArrayBuffer; 
            histogramStatistic(data); 
          }) 
      } 
      .width('100%') 
    } 
    .height('100%') 
  } 
}