连续的 ContinueWith 语句

Question

我有

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

这些方法是按顺序执行的吗？即，doSomething() 被执行，一旦完成，doSomething2() 开始，一旦完成，doSomething3() 开始

如果不是按顺序执行，有没有更好的方法呢？

Answer 1

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

Creates a continuation that executes asynchronously when the target Task completes and returns a value.

msdn reference

Answer 2

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);
    }
}

这会产生以下结果。通过查看时间，这证实了第二个 ContinueWith 仅在第一个完成后发生。

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 Fiddle

连续的 ContinueWith 语句

Consecutive ContinueWith statements

c#

asynchronous

task