连续ContinueWith语句

Question

我有过

    System.Threading.Tasks.Task.Factory.StartNew (() => {
       doSomething();
    }).ContinueWith (t => {
       doSomething2();
    }).ContinueWith (x => {
       doSomething3();
    }, TaskScheduler.FromCurrentSynchronizationContext ());

这些方法是否按顺序执行？也就是说，doSomething()被执行，一旦完成，doSomething2()就会启动，一旦完成，doSomething3()就会启动。

如果它们不是按顺序执行的，是否有更好的方法来执行？

Answer 1

对于这类问题，一个简单的方法是编写一个快速测试：

using System;
using System.Threading;
using System.Threading.Tasks;


public class Program
{
    public static void Main()
    {
        Console.WriteLine("{0}: Starting Main: Thread ID {1}", DateTime.Now.TimeOfDay, Thread.CurrentThread.ManagedThreadId);
        var finalTask = Task.Delay(500)
            .ContinueWith(_ => {
                Console.WriteLine("{0}: First Continue With: Task ID {1}, Thread ID {2}", DateTime.Now.TimeOfDay, Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(1000);
            })
            .ContinueWith(_ => {
                Console.WriteLine("{0}: Second Continue With: Task ID {1}, Thread ID {2}", DateTime.Now.TimeOfDay, Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(1000);
            });;

        finalTask.Wait();
        Console.WriteLine("{0}: Finished!", DateTime.Now.TimeOfDay);
    }
}

这将产生以下结果。通过查看“时代”，这证实了第二个ContinueWith只发生在第一个完成之后。

02:03:16.1360139: Starting Main: Thread ID 107
02:03:16.6407471: First Continue With: Task ID 1, Thread ID 272
02:03:17.6514780: Second Continue With: Task ID 2, Thread ID 272
02:03:18.6592219: Finished!

.NET填充器

Answer 2

对，是这样。它将始终按顺序执行。只有在调用任务完成后，ContinueWith才会运行。

创建一个在目标任务完成并返回值时异步执行的延续。

msdn参考