如何实现TaskPool异步任务支持串行队列

import { taskpool } from '@kit.ArkTS'; 
 
@Concurrent 
function additionDelay(delay: number): void { 
  let start: number = new Date().getTime(); 
  while (new Date().getTime() - start < delay) { 
    continue; 
  } 
} 
 
@Concurrent 
function waitForRunner(finalString: string): string { 
  return finalString; 
} 
 
async function seqRunner() { 
  let finalString: string = ""; 
  let task1: taskpool.Task = new taskpool.Task(additionDelay, 3000); 
  let task2: taskpool.Task = new taskpool.Task(additionDelay, 2000); 
  let task3: taskpool.Task = new taskpool.Task(additionDelay, 1000); 
  let task4: taskpool.Task = new taskpool.Task(waitForRunner, finalString); 
 
  let runner: taskpool.SequenceRunner = new taskpool.SequenceRunner(); 
  runner.execute(task1).then(() => { 
    finalString += 'a'; 
    console.info("seqrunner: task1 done."); 
  }); 
  runner.execute(task2).then(() => { 
    finalString += 'b'; 
    console.info("seqrunner: task2 done"); 
  }); 
  runner.execute(task3).then(() => { 
    finalString += 'c'; 
    console.info("seqrunner: task3 done"); 
  }); 
  await runner.execute(task4); 
  console.info("seqrunner: task4 done, finalString is " + finalString); 
}