c# - 为什么带有 ContinueWith 选项的第二个线程不等待第一个线程的结束？

Question

为什么第二个主题是按行开始的

var finalTask = parent.ContinueWith( .. )

不是在等待第一个线程的结束吗？这是证明新线程没有等待第一个线程结束的打印输出:

Starting main thread 1
Starting ContinueWith thread 2
0 0 0
Ending ContinueWith thread 2
ContinueWith thread is finished!
Starting child thread 3
Ends child thread 3
Starting child thread 2
Ends child thread 2
Starting child thread 1
Ends child thread 1

代码:

public static void AttachTasksToMain()
        {
            Task<Int32[]> parent = Task.Run(() =>
            {
                Console.WriteLine("Starting main thread 1");
                var results = new Int32[3];
                new Task(() => {
                    Console.WriteLine("Starting child thread 1");
                    results[0] = 0;
                    Console.WriteLine("Ends child thread 1");
                }, TaskCreationOptions.AttachedToParent).Start();

                new Task(() => {
                    Console.WriteLine("Starting child thread 2");
                    results[1] = 1;
                    Console.WriteLine("Ends child thread 2");
                }, TaskCreationOptions.AttachedToParent).Start();

                new Task(() => {
                    Console.WriteLine("Starting child thread 3");
                    results[2] = 2;
                    Console.WriteLine("Ends child thread 3");
                }, TaskCreationOptions.AttachedToParent).Start();

                //this thread finishes when all child-thread are finished!
                return results;
            });
            //parent.Wait();

            var finalTask = parent.ContinueWith(parentTask =>
            {
                Console.WriteLine("Starting ContinueWith thread 2");
                foreach (int i in parentTask.Result)
                    Console.WriteLine(i);

                Console.WriteLine("Ending ContinueWith thread 2");
            });

            finalTask.Wait();
            Console.WriteLine("ContinueWith thread is finished!");

        }

Answer 1

问题是 Task.Run。这将使用 TaskCreationOptions.DenyChildAttach 启动任务。

使用 Task.Factory.StartNew 进行简单更改，问题就解决了。那是因为这里的默认值是 TaskCreationOptions.None。

See here深入讨论差异。