Question

我正在尝试创建一个任务，该任务将等待一段时间，然后继续进行一些任务后的工作。代码如下所示。如果我使用Thread.Sleep（）作为等待时间，它将按预期工作。但是，如果我将Thread.Sleep（）更改为等待Task.Delay（），则延续将在task1完成之前发生。怎么发生的？

class Program
{
    static void Main(string[] args)
    {

        Task t1 = Task.Factory.StartNew(async () => await DoSomeVeryImportantWork(1, 3))
                              .ContinueWith((prevTask)=> { Console.WriteLine("post task work!!!"); });

        Console.WriteLine("caller after starting tasks");
        Console.ReadKey();
    }

    static async Task DoSomeVeryImportantWork(int id, int sleeptimeInSeconds)
    {
        Stopwatch stopWatch = new Stopwatch();

        Console.WriteLine($"t{id} is beginning");

        stopWatch.Start();
        //Thread.Sleep(TimeSpan.FromSeconds(sleeptimeInSeconds));
        await Task.Delay(TimeSpan.FromSeconds(sleeptimeInSeconds));
        stopWatch.Stop();

        TimeSpan ts = stopWatch.Elapsed;
        string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",
           ts.Hours, ts.Minutes, ts.Seconds,
           ts.Milliseconds / 10);
        Console.WriteLine($"t{id} sleeping time -  " + elapsedTime);
        Console.WriteLine($"t{id} has completed ");
    }

}

预期输出：（如果我使用thread.sleep（）而不是task.delay（），这也是输出

caller after starting tasks
t1 is beginning
t1 sleeping time -  00:00:03.00
t1 has completed
post task work!!!

实际输出：

caller after starting tasks
t1 is beginning
post task work!!!
t1 sleeping time -  00:00:03.01
t1 has completed

Answer 1

@Steve权利。 await返回一个新的Task-等于Task.Factory.StartNew(() => DoSomeVeryImportantWork(1, 3)) ...您有两个选择：

1）使用Task.Run()正确处理异步任务：

Task t1 = Task.Run(() => DoSomeVeryImportantWork(1, 3));
// Or
Task t1 = Task.Run(async () => await DoSomeVeryImportantWork(1, 3));

2）不要呼叫Task.Factory.StartNew()。只需调用async方法，任务就会自动启动：

Task t1 = DoSomeVeryImportantWork(1, 3);

为什么ContinueWith（）在上一个任务完成之前启动

1 个答案: