​Task的MSDN的描述如下：

【Task類的表示單個操作不會返回一個值，通常以非同步方式執行。

Task物件是一種的中心思想基於任務的非同步模式首次引入.NETFramework 4 中。

因為由執行工作Task物件通常以非同步方式執行執行緒池執行緒上而不是以同步方式在主應用程式執行緒中，可以使用Status屬性，並將IsCanceled， IsCompleted，和IsFaulted屬性，以確定任務的狀態。

大多數情況下，lambda 表示式用於指定該任務所執行的工作量。

對於返回值的操作，您使用Task類。】

1、Task的優勢

　　ThreadPool相比Thread來說具備了很多優勢，但是ThreadPool卻又存在一些使用上的不方便。比如：

• ThreadPool不支援執行緒的取消、完成、失敗通知等互動性操作；
• ThreadPool不支援執行緒執行的先後次序；
  

　　以往，如果開發者要實現上述功能，需要完成很多額外的工作，現在，FCL中提供了一個功能更強大的概念：Task。Task線上程池的基礎上進行了優化，並提供了更多的API。在FCL4.0中，如果我們要編寫多執行緒程式，Task顯然已經優於傳統的方式。

　　以下是一個簡單的任務示例：

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

namespace ConsoleApp1
{
  class Program
  {
    static void Main(string[] args)
    {
      Task t = new Task(() =>
      {
        Console.WriteLine("任務開始工作……");
        //模擬工作過程
        Thread.Sleep(5000);
      });
      t.Start();
      t.ContinueWith((task) =>
      {
        Console.WriteLine("任務完成，完成時候的狀態為：");
        Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}",task.IsCanceled,task.IsCompleted,task.IsFaulted);
      });
      Console.ReadKey();
    }
  }
}

2、Task的用法

　　2.1、建立任務

　　（一）無返回值的方式

　　方式1:

　　var t1 = new Task(() => TaskMethod("Task 1"));
　　t1.Start();
　　Task.WaitAll(t1);//等待所有任務結束 
　　注:任務的狀態:
　　Start之前為:Created
　　Start之後為:WaitingToRun 

　　方式2:

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

　　方式3:

Task.Factory.StartNew(() => TaskMethod("Task 3")); 直接非同步的方法 
　　//或者
　　var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
　　Task.WaitAll(t3);//等待所有任務結束
　　//任務的狀態:
　　Start之前為:Running
　　Start之後為:Running

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

namespace ConsoleApp1
{
  class Program
  {
    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"));
      //標記為長時間執行任務,則任務不會使用執行緒池,而在單獨的執行緒中執行。
      Task.Factory.StartNew(() => TaskMethod("Task 5"),TaskCreationOptions.LongRunning);

      #region 常規的使用方式
      Console.WriteLine("主執行緒執行業務處理.");
      //建立任務
      Task task = new Task(() =>
      {
        Console.WriteLine("使用System.Threading.Tasks.Task執行非同步操作.");
        for (int i = 0; i < 10; i++)
        {
          Console.WriteLine(i);
        }
      });
      //啟動任務,並安排到當前任務佇列執行緒中執行任務(System.Threading.Tasks.TaskScheduler)
      task.Start();
      Console.WriteLine("主執行緒執行其他處理");
      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);
    }
  }
}

　　async/await的實現方式:

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執行非同步操作.");
      for (int i = 0; i < 10; i++)
      {
        Console.WriteLine(string.Format("AsyncFunction:i={0}",i));
      }
    }

    public static void Main()
    {
      Console.WriteLine("主執行緒執行業務處理.");
      AsyncFunction();
      Console.WriteLine("主執行緒執行其他處理");
      for (int i = 0; i < 10; i++)
      {
        Console.WriteLine(string.Format("Main:i={0}",i));
      }
      Console.ReadLine();
    }
  }
}

　　（二）帶返回值的方式

　　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");
      //該任務會執行在主執行緒中
      task.RunSynchronously();
      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 常規使用方式
      //建立任務
      Task<int> getsumtask = new Task<int>(() => Getsum());
      //啟動任務,並安排到當前任務佇列執行緒中執行任務(System.Threading.Tasks.TaskScheduler)
      getsumtask.Start();
      Console.WriteLine("主執行緒執行其他處理");
      //等待任務的完成執行過程。
      getsumtask.Wait();
      //獲得任務的執行結果
      Console.WriteLine("任務執行結果：{0}",getsumtask.Result.ToString());
      #endregion
    }

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

    static int Getsum()
    {
      int sum = 0;
      Console.WriteLine("使用Task執行非同步操作.");
      for (int i = 0; i < 100; i++)
      {
        sum += i;
      }
      return sum;
    }
  }
}

async/await的實現:

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      var ret1 = AsyncGetsum();
      Console.WriteLine("主執行緒執行其他處理");
      for (int i = 1; i <= 3; i++)
        Console.WriteLine("Call Main()");
      int result = ret1.Result;         //阻塞主執行緒
      Console.WriteLine("任務執行結果：{0}",result);
    }

    async static Task<int> AsyncGetsum()
    {
      await Task.Delay(1);
      int sum = 0;
      Console.WriteLine("使用Task執行非同步操作.");
      for (int i = 0; i < 100; i++)
      {
        sum += i;
      }
      return sum;
    }
  }
}

　　2.2、組合任務.ContinueWith

　　 簡單Demo:

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      //建立一個任務
      Task<int> task = new Task<int>(() =>
      {
        int sum = 0;
        Console.WriteLine("使用Task執行非同步操作.");
        for (int i = 0; i < 100; i++)
        {
          sum += i;
        }
        return sum;
      });
      //啟動任務,並安排到當前任務佇列執行緒中執行任務(System.Threading.Tasks.TaskScheduler)
      task.Start();
      Console.WriteLine("主執行緒執行其他處理");
      //任務完成時執行處理。
      Task cwt = task.ContinueWith(t =>
      {
        Console.WriteLine("任務完成後的執行結果：{0}",t.Result.ToString());
      });
      task.Wait();
      cwt.Wait();
    }
  }
}

　　 任務的序列:

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static void Main(string[] args)
    {
      ConcurrentStack<int> stack = new ConcurrentStack<int>();

      //t1先序列
      var t1 = Task.Factory.StartNew(() =>
      {
        stack.Push(1);
        stack.Push(2);
      });

      //t2,t3並行執行
      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並行執行
      var t3 = t1.ContinueWith(t =>
      {
        int result;
        stack.TryPop(out result);
        Console.WriteLine("Task t3 result={0},Thread.CurrentThread.ManagedThreadId);
      });

      //等待t2和t3執行完
      Task.WaitAll(t2,t3);

      //t7序列執行
      var t4 = Task.Factory.StartNew(() =>
      {
        Console.WriteLine("當前集合元素個數：{0},stack.Count,Thread.CurrentThread.ManagedThreadId);
      });
      t4.Wait();
    }
  }
}

　　子任務:

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      Task<string[]> parent = new Task<string[]>(state =>
      {
        Console.WriteLine(state);
        string[] result = new string[2];
        //建立並啟動子任務
        new Task(() => { result[0] = "我是子任務1。"; },TaskCreationOptions.AttachedToParent).Start();
        new Task(() => { result[1] = "我是子任務2。"; },TaskCreationOptions.AttachedToParent).Start();
        return result;
      },"我是父任務，並在我的處理過程中建立多個子任務，所有子任務完成以後我才會結束執行。");
      //任務處理完成後執行的操作
      parent.ContinueWith(t =>
      {
        Array.ForEach(t.Result,r => Console.WriteLine(r));
      });
      //啟動父任務
      parent.Start();
      //等待任務結束 Wait只能等待父執行緒結束,沒辦法等到父執行緒的ContinueWith結束
      //parent.Wait();
      Console.ReadLine();

    }
  }
}

　　動態並行(TaskCreationOptions.AttachedToParent) 父任務等待所有子任務完成後 整個任務才算完成

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

namespace ConsoleApp1
{
  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),TaskCreationOptions.AttachedToParent,TaskScheduler.Default);
      if (current.Right != null)
        Task.Factory.StartNew(() => DisplayNode(current.Right),TaskScheduler.Default);
      Console.WriteLine("當前節點的值為{0};處理的ThreadId={1}",current.Text,Thread.CurrentThread.ManagedThreadId);
    }
  }
}

　　2.3、取消任務 CancellationTokenSource

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

namespace ConsoleApp1
{
  class Program
  {
    private static int TaskMethod(string name,int seconds,CancellationToken token)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",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("First task has been cancelled before execution");
      cts = new CancellationTokenSource();
      longTask = new Task<int>(() => TaskMethod("Task 2",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("A task has been completed with result {0}.",longTask.Result);
    }
  }
}

　　2.4、處理任務中的異常

　　單個任務:

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

namespace ConsoleApp1
{
  class Program
  {
    static int TaskMethod(string name,int seconds)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",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.WriteLine();
    }
  }
}

　　多個任務:

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

namespace ConsoleApp1
{
  class Program
  {
    static int TaskMethod(string name,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;
        });
      }
    }
  }
}

async/await的方式:

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

namespace ConsoleApp1
{
  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
      {
        //非同步的方式
        Task allTasks = Task.WhenAll(task1,task2,task3);
        await allTasks;
        //同步的方式
        //Task.WaitAll(task1,task3);
      }
      catch (NotImplementedException ex)
      {
        Console.WriteLine("task1 任務報錯!");
      }
      catch (InvalidOperationException ex)
      {
        Console.WriteLine("task2 任務報錯!");
      }
      catch (Exception ex)
      {
        Console.WriteLine("任務報錯!");
      }

    }

    public static void Main()
    {
      Task task = ObserveOneExceptionAsync();
      Console.WriteLine("主執行緒繼續執行........");
      task.Wait();
    }
  }
}

　　2.5、Task.FromResult的應用

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  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("主程式繼續執行。。。。");
      string result = task.Result;
      Console.WriteLine("result={0}",result);

    }

    private static Task<string> GetValueFromCache(string key)
    {
      Console.WriteLine("GetValueFromCache開始執行。。。。");
      string result = string.Empty;
      //Task.Delay(5000);
      Thread.Sleep(5000);
      Console.WriteLine("GetValueFromCache繼續執行。。。。");
      if (cache.TryGetValue(key,out result))
      {
        return Task.FromResult(result);
      }
      return Task.FromResult("");
    }

  }
}

　　2.6、使用IProgress實現非同步程式設計的程序通知

　　IProgress<in T>只提供了一個方法void Report(T value)，通過Report方法把一個T型別的值報告給IProgress,然後IProgress<in T>的實現類Progress<in T>的建構函式接收型別為Action<T>的形參，通過這個委託讓進度顯示在UI介面中。

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

namespace ConsoleApp1
{
  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()
    {
      //當前執行緒
      var progress = new Progress<int>(percent =>
      {
        Console.Clear();
        Console.Write("{0}%",percent);
      });
      //執行緒池執行緒
      await Task.Run(() => DoProcessing(progress));
      Console.WriteLine("");
      Console.WriteLine("結束");
    }

    public static void Main()
    {
      Task task = Display();
      task.Wait();
    }
  }
}

　　2.7、Factory.FromAsync的應用 (簡APM模式(委託)轉換為任務)(BeginXXX和EndXXX)

　　帶回調方式的

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

namespace ConsoleApp1
{
  class Program
  {
    private delegate string AsynchronousTask(string threadName);

    private static string Test(string threadName)
    {
      Console.WriteLine("Starting...");
      Console.WriteLine("Is thread pool thread: {0}",Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(2));
      Thread.CurrentThread.Name = threadName;
      return string.Format("Thread name: {0}",Thread.CurrentThread.Name);
    }

    private static void Callback(IAsyncResult ar)
    {
      Console.WriteLine("Starting a callback...");
      Console.WriteLine("State passed to a callbak: {0}",ar.AsyncState);
      Console.WriteLine("Is thread pool thread: {0}",Thread.CurrentThread.IsThreadPoolThread);
      Console.WriteLine("Thread pool worker thread id: {0}",Thread.CurrentThread.ManagedThreadId);
    }

    //執行的流程是 先執行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,"a delegate asynchronous call"),d.EndInvoke);

      task.ContinueWith(t => Console.WriteLine("Callback is finished,now running a continuation! Result: {0}",t.Result));

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

    }
  }
}

　　不帶回調方式的

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

namespace ConsoleApp1
{
  class Program
  {
    private delegate string AsynchronousTask(string threadName);

    private static string Test(string threadName)
    {
      Console.WriteLine("Starting...");
      Console.WriteLine("Is thread pool thread: {0}",Thread.CurrentThread.Name);
    }

    //執行的流程是 先執行Test--->task.ContinueWith
    static void Main(string[] args)
    {
      AsynchronousTask d = Test;
      Task<string> task = Task<string>.Factory.FromAsync(
        d.BeginInvoke,d.EndInvoke,"AsyncTaskThread","a delegate asynchronous call");
      task.ContinueWith(t => Console.WriteLine("Task is completed,t.Result));
      while (!task.IsCompleted)
      {
        Console.WriteLine(task.Status);
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
      }
      Console.WriteLine(task.Status);

    }
  }
}

//Task啟動帶引數和返回值的函式任務
//下面的例子test2 是個帶引數和返回值的函式。

private int test2(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;
}

//測試呼叫
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>(test2),i);
}

//= 下載網站原始檔例子 == == == == == == == == == == == ==
//HttpClient 引用System.Net.Http
private async Task< int> test2(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);

  //System.Threading.Thread.Sleep(3000);
  //MessageBox.Show("hello:"+ i);
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = false;
  }));
  return 0;
}

async private void call()
{
  //Func<string,string> funcOne = delegate(string s){ return "fff"; };
  object i = 55;
  var t = Task<Task<int>>.Factory.StartNew(new Func<object,Task<int>>(test2),i);
}

//----------或者----------

private async void test2()
{
  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(test2));
  //相當於
  //Thread th= new Thread(new ThreadStart(test2));
  //th.Start();
}

Task啟動帶引數和返回值的函式任務

以上就是深入分析C# Task的詳細內容，更多關於C# Task的資料請關注我們其它相關文章！