C# Task详解

1、Task的优势

　　ThreadPool相比Thread来说具备了很多优势，但是ThreadPool却又存在一些使用上的不方便。比如：
　　◆ ThreadPool不支持线程的取消、完成、失败通知等交互性操作；
　　◆ ThreadPool不支持线程执行的先后次序；
　　以往，如果开发者要实现上述功能，需要完成很多额外的工作，现在，FCL中提供了一个功能更强大的概念：Task。Task在线程池的基础上进行了优化，并提供了更多的API。在FCL4.0中，如果我们要编写多线程程序，Task显然已经优于传统的方式。
　　以下是一个简单的任务示例：

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static void Main(string[] args)
10         {
11             Task t = new Task(() =>
12             {
13                 Console.WriteLine("任务开始工作……");
14                 //模拟工作过程
15                 Thread.Sleep(5000);
16             });
17             t.Start();
18             t.ContinueWith((task) =>
19             {
20                 Console.WriteLine("任务完成，完成时候的状态为：");
21                 Console.WriteLine("IsCanceled={0}	IsCompleted={1}	IsFaulted={2}", task.IsCanceled, task.IsCompleted, task.IsFaulted);
22             });
23             Console.ReadKey();
24         }
25     }
26 }

2、Task的用法

2.1、创建任务

（一）无返回值的方式
方式1:

1 　　var t1 = new Task(() => TaskMethod("Task 1"));
2 　　t1.Start();
3 　　Task.WaitAll(t1);//等待所有任务结束 
4 　　注:任务的状态:
5 　　Start之前为:Created
6 　　Start之后为:WaitingToRun

方式2:

Task.Run(() => TaskMethod("Task 2"));

方式3:

1 　　Task.Factory.StartNew(() => TaskMethod("Task 3")); 直接异步的方法 
2 　　//或者
3 　　var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
4 　　Task.WaitAll(t3);//等待所有任务结束
5 　　//任务的状态:
6 　　Start之前为:Running
7 　　Start之后为:Running

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static void Main(string[] args)
10         {
11             var t1 = new Task(() => TaskMethod("Task 1"));
12             var t2 = new Task(() => TaskMethod("Task 2"));
13             t2.Start();
14             t1.Start();
15             Task.WaitAll(t1, t2);
16             Task.Run(() => TaskMethod("Task 3"));
17             Task.Factory.StartNew(() => TaskMethod("Task 4"));
18             //标记为长时间运行任务,则任务不会使用线程池,而在单独的线程中运行。
19             Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);
20 
21             #region 常规的使用方式
22             Console.WriteLine("主线程执行业务处理.");
23             //创建任务
24             Task task = new Task(() =>
25             {
26                 Console.WriteLine("使用System.Threading.Tasks.Task执行异步操作.");
27                 for (int i = 0; i < 10; i++)
28                 {
29                     Console.WriteLine(i);
30                 }
31             });
32             //启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
33             task.Start();
34             Console.WriteLine("主线程执行其他处理");
35             task.Wait();
36             #endregion
37 
38             Thread.Sleep(TimeSpan.FromSeconds(1));
39             Console.ReadLine();
40         }
41 
42         static void TaskMethod(string name)
43         {
44             Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
45                 name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
46         }
47     }
48 }

async/await的实现方式:

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         async static void AsyncFunction()
10         {
11             await Task.Delay(1);
12             Console.WriteLine("使用System.Threading.Tasks.Task执行异步操作.");
13             for (int i = 0; i < 10; i++)
14             {
15                 Console.WriteLine(string.Format("AsyncFunction:i={0}", i));
16             }
17         }
18 
19         public static void Main()
20         {
21             Console.WriteLine("主线程执行业务处理.");
22             AsyncFunction();
23             Console.WriteLine("主线程执行其他处理");
24             for (int i = 0; i < 10; i++)
25             {
26                 Console.WriteLine(string.Format("Main:i={0}", i));
27             }
28             Console.ReadLine();
29         }
30     }
31 }

（二）带返回值的方式
方式4:

1     Task<int> task = CreateTask("Task 1");
2     task.Start(); 
3     int result = task.Result;

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static Task<int> CreateTask(string name)
10         {
11             return new Task<int>(() => TaskMethod(name));
12         }
13 
14         static void Main(string[] args)
15         {
16             TaskMethod("Main Thread Task");
17             Task<int> task = CreateTask("Task 1");
18             task.Start();
19             int result = task.Result;
20             Console.WriteLine("Task 1 Result is: {0}", result);
21 
22             task = CreateTask("Task 2");
23             //该任务会运行在主线程中
24             task.RunSynchronously();
25             result = task.Result;
26             Console.WriteLine("Task 2 Result is: {0}", result);
27 
28             task = CreateTask("Task 3");
29             Console.WriteLine(task.Status);
30             task.Start();
31 
32             while (!task.IsCompleted)
33             {
34                 Console.WriteLine(task.Status);
35                 Thread.Sleep(TimeSpan.FromSeconds(0.5));
36             }
37 
38             Console.WriteLine(task.Status);
39             result = task.Result;
40             Console.WriteLine("Task 3 Result is: {0}", result);
41 
42             #region 常规使用方式
43             //创建任务
44             Task<int> getsumtask = new Task<int>(() => Getsum());
45             //启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
46             getsumtask.Start();
47             Console.WriteLine("主线程执行其他处理");
48             //等待任务的完成执行过程。
49             getsumtask.Wait();
50             //获得任务的执行结果
51             Console.WriteLine("任务执行结果：{0}", getsumtask.Result.ToString());
52             #endregion
53         }
54 
55         static int TaskMethod(string name)
56         {
57             Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
58                 name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
59             Thread.Sleep(TimeSpan.FromSeconds(2));
60             return 42;
61         }
62 
63         static int Getsum()
64         {
65             int sum = 0;
66             Console.WriteLine("使用Task执行异步操作.");
67             for (int i = 0; i < 100; i++)
68             {
69                 sum += i;
70             }
71             return sum;
72         }
73     }
74 }

async/await的实现:

 1 using System;
 2 using System.Threading.Tasks;
 3 
 4 namespace ConsoleApp1
 5 {
 6     class Program
 7     {
 8         public static void Main()
 9         {
10             var ret1 = AsyncGetsum();
11             Console.WriteLine("主线程执行其他处理");
12             for (int i = 1; i <= 3; i++)
13                 Console.WriteLine("Call Main()");
14             int result = ret1.Result;                  //阻塞主线程
15             Console.WriteLine("任务执行结果：{0}", result);
16         }
17 
18         async static Task<int> AsyncGetsum()
19         {
20             await Task.Delay(1);
21             int sum = 0;
22             Console.WriteLine("使用Task执行异步操作.");
23             for (int i = 0; i < 100; i++)
24             {
25                 sum += i;
26             }
27             return sum;
28         }
29     }
30 }

2.2、组合任务.ContinueWith

简单Demo:

 1 using System;
 2 using System.Threading.Tasks;
 3 
 4 namespace ConsoleApp1
 5 {
 6     class Program
 7     {
 8         public static void Main()
 9         {
10             //创建一个任务
11             Task<int> task = new Task<int>(() =>
12             {
13                 int sum = 0;
14                 Console.WriteLine("使用Task执行异步操作.");
15                 for (int i = 0; i < 100; i++)
16                 {
17                     sum += i;
18                 }
19                 return sum;
20             });
21             //启动任务,并安排到当前任务队列线程中执行任务(System.Threading.Tasks.TaskScheduler)
22             task.Start();
23             Console.WriteLine("主线程执行其他处理");
24             //任务完成时执行处理。
25             Task cwt = task.ContinueWith(t =>
26             {
27                 Console.WriteLine("任务完成后的执行结果：{0}", t.Result.ToString());
28             });
29             task.Wait();
30             cwt.Wait();
31         }
32     }
33 }

任务的串行:

 1 using System;
 2 using System.Collections.Concurrent;
 3 using System.Threading;
 4 using System.Threading.Tasks;
 5 
 6 namespace ConsoleApp1
 7 {
 8     class Program
 9     {
10         static void Main(string[] args)
11         {
12             ConcurrentStack<int> stack = new ConcurrentStack<int>();
13 
14             //t1先串行
15             var t1 = Task.Factory.StartNew(() =>
16             {
17                 stack.Push(1);
18                 stack.Push(2);
19             });
20 
21             //t2,t3并行执行
22             var t2 = t1.ContinueWith(t =>
23             {
24                 int result;
25                 stack.TryPop(out result);
26                 Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
27             });
28 
29             //t2,t3并行执行
30             var t3 = t1.ContinueWith(t =>
31             {
32                 int result;
33                 stack.TryPop(out result);
34                 Console.WriteLine("Task t3 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
35             });
36 
37             //等待t2和t3执行完
38             Task.WaitAll(t2, t3);
39 
40             //t7串行执行
41             var t4 = Task.Factory.StartNew(() =>
42             {
43                 Console.WriteLine("当前集合元素个数：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
44             });
45             t4.Wait();
46         }
47     }
48 }

子任务:

 1 using System;
 2 using System.Threading.Tasks;
 3 
 4 namespace ConsoleApp1
 5 {
 6     class Program
 7     {
 8         public static void Main()
 9         {
10             Task<string[]> parent = new Task<string[]>(state =>
11             {
12                 Console.WriteLine(state);
13                 string[] result = new string[2];
14                 //创建并启动子任务
15                 new Task(() => { result[0] = "我是子任务1。"; }, TaskCreationOptions.AttachedToParent).Start();
16                 new Task(() => { result[1] = "我是子任务2。"; }, TaskCreationOptions.AttachedToParent).Start();
17                 return result;
18             }, "我是父任务，并在我的处理过程中创建多个子任务，所有子任务完成以后我才会结束执行。");
19             //任务处理完成后执行的操作
20             parent.ContinueWith(t =>
21             {
22                 Array.ForEach(t.Result, r => Console.WriteLine(r));
23             });
24             //启动父任务
25             parent.Start();
26             //等待任务结束 Wait只能等待父线程结束,没办法等到父线程的ContinueWith结束
27             //parent.Wait();
28             Console.ReadLine();
29 
30         }
31     }
32 }

动态并行(TaskCreationOptions.AttachedToParent) 父任务等待所有子任务完成后整个任务才算完成

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Node
 8     {
 9         public Node Left { get; set; }
10         public Node Right { get; set; }
11         public string Text { get; set; }
12     }
13 
14 
15     class Program
16     {
17         static Node GetNode()
18         {
19             Node root = new Node
20             {
21                 Left = new Node
22                 {
23                     Left = new Node
24                     {
25                         Text = "L-L"
26                     },
27                     Right = new Node
28                     {
29                         Text = "L-R"
30                     },
31                     Text = "L"
32                 },
33                 Right = new Node
34                 {
35                     Left = new Node
36                     {
37                         Text = "R-L"
38                     },
39                     Right = new Node
40                     {
41                         Text = "R-R"
42                     },
43                     Text = "R"
44                 },
45                 Text = "Root"
46             };
47             return root;
48         }
49 
50         static void Main(string[] args)
51         {
52             Node root = GetNode();
53             DisplayTree(root);
54         }
55 
56         static void DisplayTree(Node root)
57         {
58             var task = Task.Factory.StartNew(() => DisplayNode(root),
59                                             CancellationToken.None,
60                                             TaskCreationOptions.None,
61                                             TaskScheduler.Default);
62             task.Wait();
63         }
64 
65         static void DisplayNode(Node current)
66         {
67 
68             if (current.Left != null)
69                 Task.Factory.StartNew(() => DisplayNode(current.Left),
70                                             CancellationToken.None,
71                                             TaskCreationOptions.AttachedToParent,
72                                             TaskScheduler.Default);
73             if (current.Right != null)
74                 Task.Factory.StartNew(() => DisplayNode(current.Right),
75                                             CancellationToken.None,
76                                             TaskCreationOptions.AttachedToParent,
77                                             TaskScheduler.Default);
78             Console.WriteLine("当前节点的值为{0};处理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
79         }
80     }
81 }

2.3、取消任务 CancellationTokenSource

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         private static int TaskMethod(string name, int seconds, CancellationToken token)
10         {
11             Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
12                 name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
13             for (int i = 0; i < seconds; i++)
14             {
15                 Thread.Sleep(TimeSpan.FromSeconds(1));
16                 if (token.IsCancellationRequested) return -1;
17             }
18             return 42 * seconds;
19         }
20 
21         private static void Main(string[] args)
22         {
23             var cts = new CancellationTokenSource();
24             var longTask = new Task<int>(() => TaskMethod("Task 1", 10, cts.Token), cts.Token);
25             Console.WriteLine(longTask.Status);
26             cts.Cancel();
27             Console.WriteLine(longTask.Status);
28             Console.WriteLine("First task has been cancelled before execution");
29             cts = new CancellationTokenSource();
30             longTask = new Task<int>(() => TaskMethod("Task 2", 10, cts.Token), cts.Token);
31             longTask.Start();
32             for (int i = 0; i < 5; i++)
33             {
34                 Thread.Sleep(TimeSpan.FromSeconds(0.5));
35                 Console.WriteLine(longTask.Status);
36             }
37             cts.Cancel();
38             for (int i = 0; i < 5; i++)
39             {
40                 Thread.Sleep(TimeSpan.FromSeconds(0.5));
41                 Console.WriteLine(longTask.Status);
42             }
43 
44             Console.WriteLine("A task has been completed with result {0}.", longTask.Result);
45         }
46     }
47 }

2.4、处理任务中的异常

单个任务:

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static int TaskMethod(string name, int seconds)
10         {
11             Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
12                 name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
13             Thread.Sleep(TimeSpan.FromSeconds(seconds));
14             throw new Exception("Boom!");
15             return 42 * seconds;
16         }
17 
18         static void Main(string[] args)
19         {
20             try
21             {
22                 Task<int> task = Task.Run(() => TaskMethod("Task 2", 2));
23                 int result = task.GetAwaiter().GetResult();
24                 Console.WriteLine("Result: {0}", result);
25             }
26             catch (Exception ex)
27             {
28                 Console.WriteLine("Task 2 Exception caught: {0}", ex.Message);
29             }
30             Console.WriteLine("----------------------------------------------");
31             Console.WriteLine();
32         }
33     }
34 }

多个任务:

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static int TaskMethod(string name, int seconds)
10         {
11             Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
12                 name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
13             Thread.Sleep(TimeSpan.FromSeconds(seconds));
14             throw new Exception(string.Format("Task {0} Boom!", name));
15             return 42 * seconds;
16         }
17 
18 
19         public static void Main(string[] args)
20         {
21             try
22             {
23                 var t1 = new Task<int>(() => TaskMethod("Task 3", 3));
24                 var t2 = new Task<int>(() => TaskMethod("Task 4", 2));
25                 var complexTask = Task.WhenAll(t1, t2);
26                 var exceptionHandler = complexTask.ContinueWith(t =>
27                         Console.WriteLine("Result: {0}", t.Result),
28                         TaskContinuationOptions.OnlyOnFaulted
29                     );
30                 t1.Start();
31                 t2.Start();
32                 Task.WaitAll(t1, t2);
33             }
34             catch (AggregateException ex)
35             {
36                 ex.Handle(exception =>
37                 {
38                     Console.WriteLine(exception.Message);
39                     return true;
40                 });
41             }
42         }
43     }
44 }

async/await的方式:

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static async Task ThrowNotImplementedExceptionAsync()
10         {
11             throw new NotImplementedException();
12         }
13 
14         static async Task ThrowInvalidOperationExceptionAsync()
15         {
16             throw new InvalidOperationException();
17         }
18 
19         static async Task Normal()
20         {
21             await Fun();
22         }
23 
24         static Task Fun()
25         {
26             return Task.Run(() =>
27             {
28                 for (int i = 1; i <= 10; i++)
29                 {
30                     Console.WriteLine("i={0}", i);
31                     Thread.Sleep(200);
32                 }
33             });
34         }
35 
36         static async Task ObserveOneExceptionAsync()
37         {
38             var task1 = ThrowNotImplementedExceptionAsync();
39             var task2 = ThrowInvalidOperationExceptionAsync();
40             var task3 = Normal();
41 
42 
43             try
44             {
45                 //异步的方式
46                 Task allTasks = Task.WhenAll(task1, task2, task3);
47                 await allTasks;
48                 //同步的方式
49                 //Task.WaitAll(task1, task2, task3);
50             }
51             catch (NotImplementedException ex)
52             {
53                 Console.WriteLine("task1 任务报错!");
54             }
55             catch (InvalidOperationException ex)
56             {
57                 Console.WriteLine("task2 任务报错!");
58             }
59             catch (Exception ex)
60             {
61                 Console.WriteLine("任务报错!");
62             }
63 
64         }
65 
66         public static void Main()
67         {
68             Task task = ObserveOneExceptionAsync();
69             Console.WriteLine("主线程继续运行........");
70             task.Wait();
71         }
72     }
73 }

2.5、Task.FromResult的应用

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Threading;
 4 using System.Threading.Tasks;
 5 
 6 namespace ConsoleApp1
 7 {
 8     class Program
 9     {
10         static IDictionary<string, string> cache = new Dictionary<string, string>()
11         {
12             {"0001","A"},
13             {"0002","B"},
14             {"0003","C"},
15             {"0004","D"},
16             {"0005","E"},
17             {"0006","F"},
18         };
19 
20         public static void Main()
21         {
22             Task<string> task = GetValueFromCache("0006");
23             Console.WriteLine("主程序继续执行。。。。");
24             string result = task.Result;
25             Console.WriteLine("result={0}", result);
26 
27         }
28 
29         private static Task<string> GetValueFromCache(string key)
30         {
31             Console.WriteLine("GetValueFromCache开始执行。。。。");
32             string result = string.Empty;
33             //Task.Delay(5000);
34             Thread.Sleep(5000);
35             Console.WriteLine("GetValueFromCache继续执行。。。。");
36             if (cache.TryGetValue(key, out result))
37             {
38                 return Task.FromResult(result);
39             }
40             return Task.FromResult("");
41         }
42 
43     }
44 }

2.6、使用IProgress实现异步编程的进程通知

　　IProgress<in T>只提供了一个方法void Report(T value)，通过Report方法把一个T类型的值报告给IProgress,然后IProgress<in T>的实现类Progress<in T>的构造函数接收类型为Action<T>的形参，通过这个委托让进度显示在UI界面中。

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         static void DoProcessing(IProgress<int> progress)
10         {
11             for (int i = 0; i <= 100; ++i)
12             {
13                 Thread.Sleep(100);
14                 if (progress != null)
15                 {
16                     progress.Report(i);
17                 }
18             }
19         }
20 
21         static async Task Display()
22         {
23             //当前线程
24             var progress = new Progress<int>(percent =>
25             {
26                 Console.Clear();
27                 Console.Write("{0}%", percent);
28             });
29             //线程池线程
30             await Task.Run(() => DoProcessing(progress));
31             Console.WriteLine("");
32             Console.WriteLine("结束");
33         }
34 
35         public static void Main()
36         {
37             Task task = Display();
38             task.Wait();
39         }
40     }
41 }

2.7、Factory.FromAsync的应用 (简APM模式(委托)转换为任务)(BeginXXX和EndXXX)

带回调方式的

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         private delegate string AsynchronousTask(string threadName);
10 
11         private static string Test(string threadName)
12         {
13             Console.WriteLine("Starting...");
14             Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
15             Thread.Sleep(TimeSpan.FromSeconds(2));
16             Thread.CurrentThread.Name = threadName;
17             return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
18         }
19 
20         private static void Callback(IAsyncResult ar)
21         {
22             Console.WriteLine("Starting a callback...");
23             Console.WriteLine("State passed to a callbak: {0}", ar.AsyncState);
24             Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
25             Console.WriteLine("Thread pool worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
26         }
27 
28         //执行的流程是 先执行Test--->Callback--->task.ContinueWith
29         static void Main(string[] args)
30         {
31             AsynchronousTask d = Test;
32             Console.WriteLine("Option 1");
33             Task<string> task = Task<string>.Factory.FromAsync(
34                 d.BeginInvoke("AsyncTaskThread", Callback, "a delegate asynchronous call"), d.EndInvoke);
35 
36             task.ContinueWith(t => Console.WriteLine("Callback is finished, now running a continuation! Result: {0}",
37                 t.Result));
38 
39             while (!task.IsCompleted)
40             {
41                 Console.WriteLine(task.Status);
42                 Thread.Sleep(TimeSpan.FromSeconds(0.5));
43             }
44             Console.WriteLine(task.Status);
45 
46         }
47     }
48 }

不带回调方式的

 1 using System;
 2 using System.Threading;
 3 using System.Threading.Tasks;
 4 
 5 namespace ConsoleApp1
 6 {
 7     class Program
 8     {
 9         private delegate string AsynchronousTask(string threadName);
10 
11         private static string Test(string threadName)
12         {
13             Console.WriteLine("Starting...");
14             Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
15             Thread.Sleep(TimeSpan.FromSeconds(2));
16             Thread.CurrentThread.Name = threadName;
17             return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
18         }
19 
20         //执行的流程是 先执行Test--->task.ContinueWith
21         static void Main(string[] args)
22         {
23             AsynchronousTask d = Test;
24             Task<string> task = Task<string>.Factory.FromAsync(
25                 d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "a delegate asynchronous call");
26             task.ContinueWith(t => Console.WriteLine("Task is completed, now running a continuation! Result: {0}",
27                 t.Result));
28             while (!task.IsCompleted)
29             {
30                 Console.WriteLine(task.Status);
31                 Thread.Sleep(TimeSpan.FromSeconds(0.5));
32             }
33             Console.WriteLine(task.Status);
34 
35         }
36     }
37 }

 1 //Task启动带参数和返回值的函数任务
 2 //下面的例子test2 是个带参数和返回值的函数。
 3 
 4 private int test2(object i)
 5 {
 6     this.Invoke(new Action(() =>
 7     {
 8         pictureBox1.Visible = true;
 9     }));
10     System.Threading.Thread.Sleep(3000);
11     MessageBox.Show("hello:" + i);
12     this.Invoke(new Action(() =>
13     {
14         pictureBox1.Visible = false;
15     }));
16     return 0;
17 }
18 
19 //测试调用
20 private void call()
21 {
22     //Func<string, string> funcOne = delegate(string s){ return "fff"; };
23     object i = 55;
24     var t = Task<int>.Factory.StartNew(new Func<object, int>(test2), i);
25 }
26 
27 //= 下载网站源文件例子 == == == == == == == == == == == ==
28 //HttpClient 引用System.Net.Http
29 private async Task< int> test2(object i)
30 {
31     this.Invoke(new Action(() =>
32     {
33         pictureBox1.Visible = true;
34     }));
35 
36     HttpClient client = new HttpClient();
37     var a = await client.GetAsync("http://www.baidu.com");
38     Task<string> s = a.Content.ReadAsStringAsync();
39     MessageBox.Show (s.Result);
40 
41     //System.Threading.Thread.Sleep(3000);
42     //MessageBox.Show("hello:"+ i);
43     this.Invoke(new Action(() =>
44     {
45         pictureBox1.Visible = false;
46     }));
47     return 0;
48 }
49 
50 async private void call()
51 {
52     //Func<string, string> funcOne = delegate(string s){ return "fff"; };
53     object i = 55;
54     var t = Task<Task<int>>.Factory.StartNew(new Func<object, Task<int>>(test2), i);
55 }
56 
57 //----------或者----------
58 
59 private async void test2()
60 {
61     this.Invoke(new Action(() =>
62     {
63         pictureBox1.Visible = true;
64     }));
65     HttpClient client = new HttpClient();
66     var a = await client.GetAsync("http://www.baidu.com");
67     Task<string> s = a.Content.ReadAsStringAsync();
68     MessageBox.Show (s.Result);
69     this.Invoke(new Action(() =>
70     {
71         pictureBox1.Visible = false;
72     }));
73 }
74 
75 private void call()
76 {
77     var t = Task.Run(new Action(test2));
78     //相当于
79     //Thread th= new Thread(new ThreadStart(test2));
80     //th.Start();
81 }

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原文地址：https://www.cnblogs.com/ybqjymy/p/14282305.html