.NET Task的新认识

当使用Task时，如果Task的实现（即代理）本身也是异步的，则Wait()会失效。

1. Wait()有效，Task的实现（即代理）本身非异步

private async void btn_task1_Click(object sender, RoutedEventArgs e)
{
this.WriteLine("btn_task1_Click++++++++++++++++++++");
Task t1 = new Task(() =>// 使用for模拟延时
{
this.WriteLine("Task 1 running..");
for (long i = 0; i < 0xfffffff; i++) ;
this.WriteLine("Task 1 end");
});

this.WriteLine("Task 1 start");
t1.Start();
this.WriteLine("Task 1 wait start");
t1.Wait();// 生效
this.WriteLine("Task 1 wait end");

this.WriteLine("btn_task1_Click delay 3s");
await Task.Delay(3000);
this.WriteLine("btn_task1_Click--------------------------------------");
}2. Wait()失效，Task的实现（即代理）本身是异步

private async void btn_task2_Click(object sender, RoutedEventArgs e)
{
this.WriteLine("btn_task2_Click++++++++++++++++++++");
Task t2 = new Task(async () =>// 使用Task.Delay延时，但Task.Delay是可等待的（即异步）
{
this.WriteLine("Task 2 running..");
await Task.Delay(2000);
this.WriteLine("Task 2 end");
});

this.WriteLine("Task 2 start");
t2.Start();
this.WriteLine("Task 2 wait start");
t2.Wait();// Wait()失效
this.WriteLine("Task 2 wait end");

this.WriteLine("btn_task2_Click delay 3s");
await Task.Delay(3000);
this.WriteLine("btn_task2_Click--------------------------------------");
}

解决异步和可等待：
如果想让Wait()有效，而Task的实现（即代理）本身又是异步的，我们只能使用Task.Run(Func<Task> function):

private async void btn_task3_Click(object sender, RoutedEventArgs e)
{
this.WriteLine("btn_task3_Click++++++++++++++++++++");
Task t3 = Task.Run(async () =>//Task.Run()创建的Task涉及到一个异步链的问题，当使用了Wait()的时候，它会等Task.Run()里面的异步执行完。
{
this.WriteLine("Task 3 running..");
await Task.Delay(2000);

this.WriteLine("Task 3 end");
});

this.WriteLine("Task 3 wait");
t3.Wait();// 有效

this.WriteLine("btn_task3_Click delay 3s");
await Task.Delay(3000);
this.WriteLine("btn_task3_Click--------------------------------------");
}