1、Task产生背景

Task出现之前，微软的多线程处理方式有：Thread→ThreadPool→委托的异步调用，虽然也可以基本业务需要的多线程场景，但它们在多个线程的等待处理方面、资源占用方面、线程延续和阻塞方面、线程的取消方面等都显得比较笨拙，在面对复杂的业务场景下，显得有点捉襟见肘了。

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；

正是在这种背景下，Task应运而生。Task是微软在.Net 4.0时代推出来的，也是微软极力推荐的一种多线程的处理方式，Task看起来像一个Thread，实际上，它是在ThreadPool的基础上进行的封装，Task的控制和扩展性很强，在线程的延续、阻塞、取消、超时等方面远胜于Thread和ThreadPool。以下是一个简单的任务示例：

static void Main(string[] args)
{
    Task t = new Task(() =>
    {
        Console.WriteLine("任务开始工作……");
        Thread.Sleep(5000);  //模拟工作过程
    });
    t.Start();
    t.ContinueWith(task =>
    {
        Console.WriteLine("任务完成，完成时候的状态为：");
        Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}", 
                          task.IsCanceled, task.IsCompleted, task.IsFaulted);
    });
    Console.ReadKey();
}

2、Task使用方法 

2.1　创建和启动任务

2.1.1 无返回值的方式

方式1:调用Start方法

var t1 = new Task(() => TaskMethod("Task 1"));
t1.Start();
Task.WaitAll(t1);//等待所有任务结束 

任务的状态：Start之前为Created，之后为WaitingToRun 

方式2:静态方法Run

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

方式3:TaskFactory工厂

// 方法1. TaskFactory工厂
TaskFactory taskFactory = new TaskFactory() ;
taskFactory.StartNew(() => TaskMethod("Task 3"));
// 方法2. Task.Factory属性
Task.Factory.StartNew(() => TaskMethod("Task 3"));
//或者
var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
Task.WaitAll(t3);

 任务的状态：Start之前为Running，之后为Running

static void Main(string[] args)
{
    var t1 = new Task(() => TaskMethod("Task 1"));
    var t2 = new Task(() => TaskMethod("Task 2"));
    t2.Start();
    t1.Start();
    Task.WaitAll(t1, t2);
    Task.Run(() => TaskMethod("Task 3"));
    Task.Factory.StartNew(() => TaskMethod("Task 4"));
    //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。
    Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);
    
    #region 常规的使用方式
    Console.WriteLine("主线程执行业务处理.");
    //创建任务
    Task task = new Task(() =>
                         {
                             Console.WriteLine("使用`System.Threading.Tasks.Task`执行异步操作.");
                             for (int i = 0; i < 10; i++)
                             {
                                 Console.WriteLine(i);
                             }
                         });
    //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)
    task.Start();
    Console.WriteLine("主线程执行其他处理");
    task.Wait();
    #endregion

    Thread.Sleep(TimeSpan.FromSeconds(1));
    Console.ReadLine();
}

static void TaskMethod(string name)
{
    Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                      name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
}

方式4:RunSynchronously同步启动

Task实例化后调用同步方法RunSynchronously，进行线程启动。(PS: 类似委托开启线程，BeginInvoke是异步，而Invoke是同步)

var task = new Task(() => TaskMethod("Task 1"));
task.RunSynchronously();

async/await的实现方式

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        async static void AsyncFunction()
        {
            await Task.Delay(1);
            Console.WriteLine("使用`System.Threading.Tasks.Task`执行异步操作.");
            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine(string.Format("AsyncFunction:i={0}", i));
            }
        }

        public static void Main()
        {
            Console.WriteLine("主线程执行业务处理.");
            AsyncFunction();
            Console.WriteLine("主线程执行其他处理");
            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine(string.Format("Main:i={0}", i));
            }
            Console.ReadLine();
        }
    }
}

2.1.2 带返回值的方式

方式4:

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

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static Task<int> CreateTask(string name)
        {
            return new Task<int>(() => TaskMethod(name));
        }

        static void Main(string[] args)
        {
            TaskMethod("Main Thread Task");
            Task<int> task = CreateTask("Task 1");
            task.Start();
            int result = task.Result;
            Console.WriteLine("Task 1 Result is: {0}", result);

            task = CreateTask("Task 2"); 
            task.RunSynchronously(); //该任务会运行在主线程中
            result = task.Result;
            Console.WriteLine("Task 2 Result is: {0}", result);

            task = CreateTask("Task 3");
            Console.WriteLine(task.Status);
            task.Start();

            while (!task.IsCompleted)
            {
                Console.WriteLine(task.Status);
                Thread.Sleep(TimeSpan.FromSeconds(0.5));
            }

            Console.WriteLine(task.Status);
            result = task.Result;
            Console.WriteLine("Task 3 Result is: {0}", result);

            #region 常规使用方式
            //创建任务
            Task<int> getsumtask = new Task<int>(() => Getsum());
            //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)
            getsumtask.Start();
            Console.WriteLine("主线程执行其他处理");
            getsumtask.Wait(); //等待任务的完成执行过程
            Console.WriteLine("任务执行结果：{0}", getsumtask.Result.ToString());//获得任务的执行结果
            #endregion
        }

        static int TaskMethod(string name)
        {
            Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(2));
            return 42;
        }

        static int Getsum()
        {
            int sum = 0;
            Console.WriteLine("使用`Task`执行异步操作.");
            for (int i = 0; i < 100; i++)
            {
                sum += i;
            }
            return sum;
        }
    }
}

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        public static void Main()
        {
            var ret1 = AsyncGetsum();
            Console.WriteLine("主线程执行其他处理");
            for (int i = 1; i <= 3; i++)
                Console.WriteLine("Call Main()");
            int result = ret1.Result;     //阻塞主线程
            Console.WriteLine("任务执行结果：{0}", result);
        }

        async static Task<int> AsyncGetsum()
        {
            await Task.Delay(1);
            int sum = 0;
            Console.WriteLine("使用`Task`执行异步操作.");
            for (int i = 0; i < 100; i++)
            {
                sum += i;
            }
            return sum;
        }
    }
}

2.2　线程等待、延续和组合

2.2.1 Task的线程等待和延续主要以下几类：

• Wait：针对单个Task的实例，可以task1.wait进行线程等待
• WaitAny：线程列表中任何一个线程执行完毕即可执行（阻塞主线程）
• WaitAll：线程列表中所有线程执行完毕方可执行（阻塞主线程）
• WhenAny：与ContinueWith配合,线程列表中任何一个执行完毕，则继续ContinueWith中的任务（开启新线程，不阻塞主线程）
• WhenAll：与ContinueWith配合,线程列表中所有线程执行完毕，则继续ContinueWith中的任务（开启新线程，不阻塞主线程）
• ContinueWith：与WhenAny或WhenAll配合使用
• ContinueWhenAny：等价于Task的WhenAny+ContinueWith
• ContinueWhenAll：等价于Task的WhenAll+ContinueWith

  public static void Main()
  {
      //创建一个任务
      Task<int> task = new Task<int>(() =>
      {
          int sum = 0;
          Console.WriteLine("使用`Task`执行异步操作.");
          for (int i = 0; i < 100; i++)
          {
              sum += i;
          }
          return sum;
      });
      //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)
      task.Start();
      Console.WriteLine("主线程执行其他处理");
      //任务完成时执行处理。
      Task cwt = task.ContinueWith(t =>
      {
          Console.WriteLine("任务完成后的执行结果：{0}", t.Result.ToString());
      });
      task.Wait();
      cwt.Wait();
      
      Action<string,int> log = (name,time) =>
      {
          Console.WriteLine($"{name}任务开始...");
          Thread.Sleep(time);
          Console.WriteLine($"{name}任务结束!");
      };
      List<Task> tasks = new List<Task>
      {
          Task.Run(() => log("张三",3000)),
          Task.Run(() => log("李四",1000)),
          Task.Run(() => log("王五",2000))
      };
      //以下语句逐个测试效果
      Task.WaitAny(tasks.ToArray());
      Task.WaitAll(tasks.ToArray());
      Task.WhenAny(tasks.ToArray()).ContinueWith(x => Console.WriteLine("某个Task执行完毕"));
      Task.WhenAll(tasks.ToArray()).ContinueWith(x => Console.WriteLine("所有Task执行完毕"));
      Task.Factory.ContinueWhenAny(tasks.ToArray(), x => Console.WriteLine("某个Task执行完毕"));
      Task.Factory.ContinueWhenAll(tasks.ToArray(), x => Console.WriteLine("所有Task执行完毕"));
      Console.Read();
  }

  2.2.2 任务的串行

  static void Main(string[] args)
  {
      ConcurrentStack<int> stack = new ConcurrentStack<int>();
  
      //t1先串行
      var t1 = Task.Factory.StartNew(() =>
      {
          stack.Push(1);
          stack.Push(2);
      });
  
      //t2,t3并行执行
      var t2 = t1.ContinueWith(t =>
      {
          int result;
          stack.TryPop(out result);
          Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
      });
  
      //t2,t3并行执行
      var t3 = t1.ContinueWith(t =>
      {
          int result;
          stack.TryPop(out result);
          Console.WriteLine("Task t3 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
      });
  
      //等待t2和t3执行完
      Task.WaitAll(t2, t3);
  
      //t4串行执行
      var t4 = Task.Factory.StartNew(() =>
      {
          Console.WriteLine("当前集合元素个数：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
      });
      t4.Wait();
  }

  2.2.3 子任务

  public static void Main()
  {
      Task<string[]> parent = new Task<string[]>(state =>
      {
          Console.WriteLine(state);
          string[] result = new string[2];
          //创建并启动子任务
          new Task(() => { result[0] = "我是子任务1"; }, TaskCreationOptions.AttachedToParent).Start();
          new Task(() => { result[1] = "我是子任务2"; }, TaskCreationOptions.AttachedToParent).Start();
          return result;
      }, "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");
      //任务完成后执行
      parent.ContinueWith(t =>
      {
          Array.ForEach(t.Result, r => Console.WriteLine(r));
      });    
      parent.Start(); //启动父任务
      parent.Wait();//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
      Console.ReadLine();
  }

  2.2.4 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

  class Node
  {
      public Node Left { get; set; }
      public Node Right { get; set; }
      public string Text { get; set; }
  }
  
  class Program
  {
      static Node GetNode()
      {
          Node root = new Node
          {
              Left = new Node
              {
                  Left = new Node{ Text = "L-L" },
                  Right = new Node{ Text = "L-R" },
                  Text = "L"
              },
              Right = new Node
              {
                  Left = new Node{ Text = "R-L" },
                  Right = new Node{ Text = "R-R" },
                  Text = "R"
              },
              Text = "Root"
          };
          return root;
      }
  
      static void Main(string[] args)
      {
          Node root = GetNode();
          DisplayTree(root);
      }
  
      static void DisplayTree(Node root)
      {
          var task = Task.Factory.StartNew(() => DisplayNode(root),
                                          CancellationToken.None,
                                          TaskCreationOptions.None,
                                          TaskScheduler.Default);
          task.Wait();
      }
  
      static void DisplayNode(Node current)
      {
  
          if (current.Left != null)
              Task.Factory.StartNew(() => DisplayNode(current.Left),
                                          CancellationToken.None,
                                          TaskCreationOptions.AttachedToParent,
                                          TaskScheduler.Default);
          if (current.Right != null)
              Task.Factory.StartNew(() => DisplayNode(current.Right),
                                          CancellationToken.None,
                                          TaskCreationOptions.AttachedToParent,
                                          TaskScheduler.Default);
          Console.WriteLine("当前节点的值为{0};处理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
      }
  }

  2.3　取消任务

  private static int TaskMethod(string name, int seconds, CancellationToken token)
  {
      Console.WriteLine("Task {0} 正在运行,当前线程id {1}. Is thread pool thread: {2}",
          name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      for (int i = 0; i < seconds; i++)
      {
          Thread.Sleep(TimeSpan.FromSeconds(1));
          if (token.IsCancellationRequested) return -1;
      }
      return 42 * seconds;
  }
  
  private static void Main(string[] args)
  {
      var cts = new CancellationTokenSource();
      var longTask = new Task<int>(() => TaskMethod("Task 1", 10, cts.Token), cts.Token);
      Console.WriteLine(longTask.Status);
      cts.Cancel();
      Console.WriteLine(longTask.Status);
      Console.WriteLine("第一个任务在执行前已被取消");
      cts = new CancellationTokenSource();
      longTask = new Task<int>(() => TaskMethod("Task 2", 10, cts.Token), cts.Token);
      longTask.Start();
      for (int i = 0; i < 5; i++)
      {
          Thread.Sleep(TimeSpan.FromSeconds(0.5));
          Console.WriteLine(longTask.Status);
      }
      cts.Cancel();
      for (int i = 0; i < 5; i++)
      {
          Thread.Sleep(TimeSpan.FromSeconds(0.5));
          Console.WriteLine(longTask.Status);
      }
  
      Console.WriteLine("任务已完成,结果为 {0}.", longTask.Result);
  }

  2.4　处理异常

  2.4.1 单个任务

  static int TaskMethod(string name, int seconds)
  {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
          name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(seconds));
      throw new Exception("Boom!");
      return 42 * seconds;
  }
  
  static void Main(string[] args)
  {
      try
      {
          Task<int> task = Task.Run(() => TaskMethod("Task 2", 2));
          int result = task.GetAwaiter().GetResult();
          Console.WriteLine("Result: {0}", result);
      }
      catch (Exception ex)
      {
          Console.WriteLine("Task 2 Exception caught: {0}", ex.Message);
      }
      Console.WriteLine("----------------------------------------------");
      Console.ReadLine();
  }

  2.4.2 多个任务

  static int TaskMethod(string name, int seconds)
  {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
          name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(seconds));
      throw new Exception(string.Format("Task {0} Boom!", name));
      return 42 * seconds;
  }
  
  public static void Main(string[] args)
  {
      try
      {
          var t1 = new Task<int>(() => TaskMethod("Task 3", 3));
          var t2 = new Task<int>(() => TaskMethod("Task 4", 2));
          var complexTask = Task.WhenAll(t1, t2);
          var exceptionHandler = complexTask.ContinueWith(t =>
                  Console.WriteLine("Result: {0}", t.Result),
                  TaskContinuationOptions.OnlyOnFaulted
              );
          t1.Start();
          t2.Start();
          Task.WaitAll(t1, t2);
      }
      catch (AggregateException ex)
      {
          ex.Handle(exception =>
          {
              Console.WriteLine(exception.Message);
              return true;
          });
      }
  }

  2.4.3 async/await的方式

  class Program
  {
      static async Task ThrowNotImplementedExceptionAsync()
      {
          throw new NotImplementedException();
      }
  
      static async Task ThrowInvalidOperationExceptionAsync()
      {
          throw new InvalidOperationException();
      }
  
      static async Task Normal()
      {
          await Fun();
      }
  
      static Task Fun()
      {
          return Task.Run(() =>
          {
              for (int i = 1; i <= 10; i++)
              {
                  Console.WriteLine("i={0}", i);
                  Thread.Sleep(200);
              }
          });
      }
  
      static async Task ObserveOneExceptionAsync()
      {
          var task1 = ThrowNotImplementedExceptionAsync();
          var task2 = ThrowInvalidOperationExceptionAsync();
          var task3 = Normal();
          try
          {
              Task allTasks = Task.WhenAll(task1, task2, task3); //异步的方式
              await allTasks;
              //Task.WaitAll(task1, task2, task3); //同步的方式
          }
          catch (NotImplementedException ex)
          {
              Console.WriteLine("task1 任务报错!");
          }
          catch (InvalidOperationException ex)
          {
              Console.WriteLine("task2 任务报错!");
          }
          catch (Exception ex)
          {
              Console.WriteLine("任务报错!");
          }
      }
  
      public static void Main()
      {
          Task task = ObserveOneExceptionAsync();
          Console.WriteLine("主线程继续运行........");
          task.Wait();
      }
  }

  2.5　Task.FromResult

  此方法创建一个Task<TResult>对象，该对象的Task<TResult>.Result属性为result，其Status属性为RanToCompletion。 当立即知道任务的返回值而不执行更长的代码路径时，通常使用方法。

  class Program
  {
      static IDictionary<string, string> cache = new Dictionary<string, string>()
      {
          {"0001","A"}, {"0002","B"}, {"0003","C"},
          {"0004","D"}, {"0005","E"}, {"0006","F"}
      };
  
      public static void Main()
      {
          Task<string> task = GetValueFromCache("0006");
          Console.WriteLine("主程序继续执行。。。。");
          string result = task.Result;
          Console.WriteLine("result={0}", result);
      }
  
      private static Task<string> GetValueFromCache(string key)
      {
          Console.WriteLine("GetValueFromCache开始执行。。。。");
          string result = string.Empty;
          //Task.Delay(5000);
          Thread.Sleep(5000);
          Console.WriteLine("GetValueFromCache继续执行。。。。");
          if (cache.TryGetValue(key, out result))
          {
              return Task.FromResult(result);
          }
          return Task.FromResult("");
      }
  }

  2.6　Factory.FromAsync

  简APM模式（委托）转换为任务，BeginXXX和EndXXX

  2.6.1 带回调方式的

  class Program
  {
      private delegate string AsynchronousTask(string threadName);
      private static string Test(string threadName)
      {
          Console.WriteLine("开始...");
          Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
          Thread.Sleep(TimeSpan.FromSeconds(2));
          Thread.CurrentThread.Name = threadName;
          return string.Format("线程名称: {0}", Thread.CurrentThread.Name);
      }
  
      private static void Callback(IAsyncResult ar)
      {
          Console.WriteLine("开始一个回调...");
          Console.WriteLine("传递给callbak的状态: {0}", ar.AsyncState);
          Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
          Console.WriteLine("线程池工作线程id: {0}", Thread.CurrentThread.ManagedThreadId);
      }
  
      //执行的流程是:先执行Test--->Callback--->task.ContinueWith
      static void Main(string[] args)
      {
          AsynchronousTask d = Test;
          Console.WriteLine("Option 1");
          Task<string> task = Task<string>.Factory.FromAsync(
              d.BeginInvoke("AsyncTaskThread", Callback, "委托异步调用"), d.EndInvoke);
          task.ContinueWith(t => Console.WriteLine("完成回调, 现在继续! Result: {0}", t.Result));
          while (!task.IsCompleted)
          {
              Console.WriteLine(task.Status);
              Thread.Sleep(TimeSpan.FromSeconds(0.5));
          }
          Console.WriteLine(task.Status);
      }
  }

  2.6.2 不带回调方式的

  class Program
  {
      private delegate string AsynchronousTask(string threadName);
      private static string Test(string threadName)
      {
          Console.WriteLine("开始...");
          Console.WriteLine("线程池是线程吗: {0}", Thread.CurrentThread.IsThreadPoolThread);
          Thread.Sleep(TimeSpan.FromSeconds(2));
          Thread.CurrentThread.Name = threadName;
          return string.Format("线程名称: {0}", Thread.CurrentThread.Name);
      }
  
      //执行的流程是:先执行Test--->task.ContinueWith
      static void Main(string[] args)
      {
          AsynchronousTask d = Test;
          Task<string> task = Task<string>.Factory.FromAsync(
              d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "委托异步调用");
          task.ContinueWith(t => Console.WriteLine("任务完成，现在运行一个延续! Result: {0}", t.Result));
          while (!task.IsCompleted)
          {
              Console.WriteLine(task.Status);
              Thread.Sleep(TimeSpan.FromSeconds(0.5));
          }
          Console.WriteLine(task.Status);
      }
  }

  2.6.3 Task启动带参数和返回值的函数任务

  方法1

  private int MyTest(object i)
  {
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = true;
      }));
      System.Threading.Thread.Sleep(3000);
      MessageBox.Show("hello:" + i);
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = false;
      }));
      return 0;
  }
  
  private void Call()
  {
      //Func<string, string> funcOne = delegate(string s){ return "fff"; };
      object i = 55;
      var t = Task<int>.Factory.StartNew(new Func<object, int>(MyTest), i);
  }

  方法2

  private async Task<int> MyTest(object i)
  {
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = true;
      }));
  
      HttpClient client = new HttpClient();
      var a = await client.GetAsync("http://www.baidu.com");
      Task<string> s = a.Content.ReadAsStringAsync();
      MessageBox.Show (s.Result);
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = false;
      }));
      return 0;
  }
  
  async private void Call()
  {
      object i = 55;
      var t = Task<Task<int>>.Factory.StartNew(new Func<object, Task<int>>(MyTest), i);
  }

  方法3

  private async void MyTest()
  {
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = true;
      }));
      HttpClient client = new HttpClient();
      var a = await client.GetAsync("http://www.baidu.com");
      Task<string> s = a.Content.ReadAsStringAsync();
      MessageBox.Show (s.Result);
      this.Invoke(new Action(() =>
      {
          pictureBox1.Visible = false;
      }));
  }
  
  private void Call()
  {
      var t = Task.Run(new Action(MyTest));
      //相当于
      //Thread th= new Thread(new ThreadStart(MyTest));
      //th.Start();
  }

  2.7　使用IProgress

  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。

  class Program
  {
      static void DoProcessing(IProgress<int> progress)
      {
          for (int i = 0; i <= 100; ++i)
          {
              Thread.Sleep(100);
              if (progress != null)
              {
                  progress.Report(i);
              }
          }
      }
  
      static async Task Display()
      {
          //当前线程
          var progress = new Progress<int>(percent =>
          {
              Console.Clear();
              Console.Write("{0}%", percent);
          });
          //线程池线程
          await Task.Run(() => DoProcessing(progress));
          Console.WriteLine("");
          Console.WriteLine("结束");
      }
  
      public static void Main()
      {
          Task task = Display();
          task.Wait();
      }
  }