.NET Task的新认识

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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--------------------------------------");}

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