重要方法

Task< Task > WhenAny 任何一个Task完成，Task就完成

Task< TResult[] > WhenAll 所有Task完成，Task才完成

Task<string> task1 = File.ReadAllTextAsync(@"Z:\file\file_1.txt");
Task<string> task2 = File.ReadAllTextAsync(@"Z:\file\file_2.txt");
Task<string> task3 = File.ReadAllTextAsync(@"Z:\file\file_3.txt");

string[] strings = await Task.WhenAll(task1, task2, task3);


string s1 = strings[0];
string s2 = strings[1]; 
string s3 = strings[2];

Console.WriteLine(s1.Substring(0,10));
Console.WriteLine(s2.Substring(0, 10));
Console.WriteLine(s3.Substring(0, 10));