1 static void Main(string[] args)
 2 {
 3     CountdownEvent countdown = new CountdownEvent(3);
 4     int taskid = 1;
 5     for
 
 (var i = 0; i < 3; i++)
 6     {
 7         Task.Factory.StartNew(() =>
 8         {
 9             int cur = taskid++;
10             Console.WriteLine($"Task[{cur}] is Running");
11             Thread.Sleep(taskid * 1000);
12             countdown.Signal();
13             Console.WriteLine($"Task[{cur}] exit
 
");
14         });
15     }
16     Console.WriteLine($"Main wait");
17     countdown.Wait();
18     Console.WriteLine($"Main exit");
19     Console.ReadKey();
20 }

CountdownEvent 與Barrier類似，但是在多次等待中，使用Barrier更加方便。

[.net 多線程]CountdownEvent