C#嵌套任务和子任务

 public class Program
    {
        static void Main(string[] args)
        { 
            WaitForSimpleNestedTask();
            Console.WriteLine("=====================================================");
            SimpleNestedTask();
            Thread.SpinWait(600000);//等待SimpleNestedTask结束 再运行
            Console.WriteLine("=====================================================");
            //SimpleNestedTaskAttachedToParent();
            Console.Read();
        }
        static void WaitForSimpleNestedTask()
        {
            var outer = Task<int>.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer1 task executing.");

                var nested = Task<int>.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested1 task starting.");
                    Thread.SpinWait(5000000);
                    Console.WriteLine("Nested1 task completing.");
                    return 42;
                });

                // 父任务等待子任务完成
                return nested.Result;
                // 父任务不等待子任务完成
                //return 1;
            });
            //输出的时候使用了返回值outer.Result，所以自动等待父任务完成
            Console.WriteLine("Outer1 has returned {0}.", outer.Result);
        }
        static void SimpleNestedTask()
        {
            var parent = Task.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer2 task executing.");

                var child = Task.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested2 task starting.");
                    Thread.SpinWait(500000);
                    Console.WriteLine("Nested2 task completing.");
                });
            });
            //等待父任务完成，再输出字符串，如果没有这个等待，这句话会先输出
            parent.Wait();
            Console.WriteLine("Outer2 has completed."); 
        }

        static void SimpleNestedTaskAttachedToParent()
        {
            var parent = Task.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer3 task executing.");

                var child = Task.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested3 task starting.");
                    Thread.SpinWait(500000);
                    Console.WriteLine("Nested3 task completing.");
                }, TaskCreationOptions.AttachedToParent);
                //增加参数TaskCreationOptions.AttachedToParent，将子任务附加进父任务，这样子任务完成后，父任务才算完成。
            });
            
            //等待父任务完成，再输出字符串，如果没有这个等待，这句话会先输出
            parent.Wait();
            Console.WriteLine("Outer has completed.");
        }