C#--多线程--Task和各种任务阻塞、延续及其线程锁Lock和Task中的跨线程访问控件和UI耗时任务卡顿的解决方法

Thread线程和ThreadPool线程池

Thread：我们可以开启一个线程。但是请大家记住：线程开启会在空间和时间上有不小的开销。所以，不能随便开。

ThreadPool：会根据你的CPU的核心数开启一个最合适的线程数量。如果你操作中，非常耗时，就不要用线程池，如果耗时十几分钟，那就不合适线程池了。

Task=>Thread + ThreadPool结合 ，使用多线程，尽量使用Task

#region Task使用【1】多线程任务的开启3种方式
 
    //【1】通过new的方式创建一个Task对象，并启动
    static void Method1_1()
    {
        Task task1 = new Task(() =>
        {
            //在这个地方编写我们需要的逻辑...
 
            Console.WriteLine($"new一个新的Task启动的子线程Id={Thread.CurrentThread.ManagedThreadId}");
        });
        task1.Start();
    }
 
    //【2】使用Task的Run（）方法
    static void Method1_2()
    {
        Task task2 = Task.Run(() =>
          {
              //在这个地方编写我们需要的逻辑...
 
              Console.WriteLine($"使用Task的Run（）方法开启的子线程Id={Thread.CurrentThread.ManagedThreadId}");
          });
    }
    //1和2对比
    //1，灵活开启线程，想什么时候开启就什么时候开启 
    //2, 马上开启线程
 
    //【3】使用TaskFactory启动（类似于ThreadPool）
    static void Method1_3()
    {
        Task task3 = Task.Factory.StartNew(() =>
        {
            //在这个地方编写我们需要的逻辑...
 
            Console.WriteLine($"使用TaskFactory开启的子线程Id={Thread.CurrentThread.ManagedThreadId}");
        });
    }
 
    #endregion
 
    #region Task使用【2】Task的阻塞方式和任务延续
 
    //【1】回顾之前使用Thread多个子线程执行时阻塞的方法
    static void Method2()
    {
        Thread thread1 = new Thread(() =>
        {
            Thread.Sleep(2000);
            Console.WriteLine("Child Thread (1)......");
        });
        Thread thread2 = new Thread(() =>
        {
            Thread.Sleep(1000);
            Console.WriteLine("Child Thread (2)......");
        });
        thread1.Start();
        thread2.Start();
        //...
 
        thread1.Join();//让调用线程阻塞
        thread2.Join();
        //如果有很多的thread，是不是也得有很多的Join？还有，我们只希望其中一个执行完以后，后面的其他线程就能执行，这个也做不了！
 
        Console.WriteLine("This is Main Thread!");
    }
    //【2】Task各种【阻塞】方式（3个）
    static void Method3()
    {
        Task task1 = new Task(() =>
         {
             Thread.Sleep(1000);
             Console.WriteLine($"Task1子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
         });
        task1.Start();
        Task task2 = new Task(() =>
        {
            Thread.Sleep(2000);
            Console.WriteLine($"Task2子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
        task2.Start();
 
        ////第1种方式：挨个等待和前面一样
        //task1.Wait();
        //task2.Wait();
 
        ////第2种方式：等待所有的任务完成    【推荐】
        Task.WaitAll(task1, task2);
 
        //第3种方式：等待任何一个完成即可  【推荐】
        //Task.WaitAny(task1, task2);
 
        Console.WriteLine("主线程开始运行！Time=" + DateTime.Now.ToLongTimeString());
 
        /*
        第2中方式结果：
        Task1子线程Id=4  21:46:58
        Task2子线程Id=3  21:46:59
        主线程开始运行！Time=21:46:59
 
        第3种方式结果
        Task1子线程Id = 3  21:41:34
        主线程开始运行！Time = 21:41:34
        Task2子线程Id = 4  21:41:35
        */
    }
 
    //Task任务的延续：WhenAll 希望前面所有任务执行完毕后，再继续执行后面的线程，和前面相比，既有阻塞，又有延续。
    static void Method4()
    {
        Task task1 = new Task(() =>
        {
            Thread.Sleep(1000);
            Console.WriteLine($"Task1子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
        task1.Start();
        Task task2 = new Task(() =>
        {
            Thread.Sleep(2000);
            Console.WriteLine($"Task2子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
        task2.Start();
 
        //线程的延续（主线程不等待，子线程依次执行，如果你需要主线程也按照子线程的顺序来，请你自己把主线程的任务放到延续任务中就可以）
        //线运行主线程，然后task1和task2都执行完，再执行task3
        Task.WhenAll(task1, task2).ContinueWith(task3 =>
         {
             //在这里可以编写你需要的业务...
 
             Console.WriteLine($"Task3子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
         });
 
        Console.WriteLine("主线程开始运行！Time=" + DateTime.Now.ToLongTimeString());
 
        /*
        主线程开始运行！Time = 21:44:46
        Task1子线程Id = 3  21:44:47
        Task2子线程Id = 4  21:44:48
        Task3子线程Id = 3  21:44:48
        */
    }
 
    //Task的延续：WhenAny
    static void Method5()
    {
        Task task1 = new Task(() =>
        {
            Thread.Sleep(1000);
            Console.WriteLine($"Task1子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
        task1.Start();
        Task task2 = new Task(() =>
        {
            Thread.Sleep(2000);
            Console.WriteLine($"Task2子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
        task2.Start();
 
        //线程的延续（主线程不等待，子线程任何一个执行完毕，就会执行后面的线程）
        Task.WhenAny(task1, task2).ContinueWith(task3 =>
        {
            //在这里可以编写你需要的业务...
 
            Console.WriteLine($"Task3子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        });
 
        Console.WriteLine("主线程开始运行！Time=" + DateTime.Now.ToLongTimeString());
 
        /*
        主线程开始运行！Time=21:48:51
        Task1子线程Id=3  21:48:52
        Task3子线程Id=6  21:48:52
        Task2子线程Id=4  21:48:53
        */
    }
 
    #endregion
 
    #region Task使用【3】Task常见枚举 TaskCreationOptions（父子任务运行、长时间运行的任务处理）
 
    //请大家通过Task的构造方法，观察TaskCreationOptions这个枚举的类型，自己通过F12查看
    static void Method6()
    {
        Task parentTask = new Task(() =>
         {
             Task task1 = new Task(() =>
              {
                  Thread.Sleep(1000);
                  Console.WriteLine($"Task1子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
              }, TaskCreationOptions.AttachedToParent);
 
             Task task2 = new Task(() =>
             {
                 Thread.Sleep(3000);
                 Console.WriteLine($"Task2子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
             }, TaskCreationOptions.AttachedToParent);
             task1.Start();
             task2.Start();
         });
 
        parentTask.Start();
        parentTask.Wait();//等待附加的子任务全部完成。相当于Task.WaitAll(taks1,task2);
        //TaskCreationOptions.AttachedToParent如果这个枚举参数不添加，主线程会直接运行，不等待
        Console.WriteLine("主线程开始执行！Time=  " + DateTime.Now.ToLongTimeString());
 
        /*
        Task1子线程Id=4  21:52:17
        Task2子线程Id=5  21:52:19
        主线程开始执行！Time=  21:52:19
         */
    }
 
    //长时间的任务运行，需要采取的方法
    static void Method7()
    {
        Task task1 = new Task(() =>
        {
            Thread.Sleep(2000);
            Console.WriteLine($"Task1子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
        }, TaskCreationOptions.LongRunning);
 
        //LongRunning：如果你明确知道这个任务是长时间运行的，建议你加上。
        //当然你使用Thread也是可以的。但是不要使用ThreadPool，因为长时间占用不归还线程，系统会强制开启新的线程，会一定程度影响性能
        task1.Start();
        task1.Wait();
 
        Console.WriteLine("主线程开始执行！Time=  " + DateTime.Now.ToLongTimeString());
 
        /*
         Task1子线程Id=3  21:57:42
        主线程开始执行！Time=  21:57:42
         */
    }
    #endregion
 
    #region  Task使用【4】Task中的取消功能：使用的是CacellationTokenSoure解决多任务中协作取消和超时取消方法
 
    //【1】Task任务的取消和判断
    static void Method8()
    {
        //创建取消信号源对象
        CancellationTokenSource cts = new CancellationTokenSource();
        Task task = Task.Factory.StartNew(() =>
        {
            int i = 0;
            while (!cts.IsCancellationRequested) //判断任务是否被取消
            {
                Thread.Sleep(200);
                i++;
                Console.WriteLine(
                    $"执行次数:{i},子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
            }
        }, cts.Token);
 
        //我们在这个地方模拟一个事件产生,如果发生某个错误，就取消线程
        Thread.Sleep(2000);
        cts.Cancel(); //取消任务，只要传递这样一个信号就可以
 
        /*
        执行次数:1,子线程Id=3  22:06:18
        执行次数:2,子线程Id=3  22:06:18
        执行次数:3,子线程Id=3  22:06:18
        执行次数:4,子线程Id=3  22:06:18
        执行次数:5,子线程Id=3  22:06:19
        执行次数:6,子线程Id=3  22:06:19
        执行次数:7,子线程Id=3  22:06:19
        执行次数:8,子线程Id=3  22:06:19
        执行次数:9,子线程Id=3  22:06:19
        执行次数:10,子线程Id=3  22:06:20
        */
    }
 
    //【2】Task任务取消：同时我们也希望做一些清理的工作，也就是取消这个动作会触发一个任务。
    static void Method9()
    {
        CancellationTokenSource cts = new CancellationTokenSource();
        Task task = Task.Factory.StartNew(() =>
        {
            while (!cts.IsCancellationRequested)
            {
                Thread.Sleep(500);
 
                Console.WriteLine($"子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
            }
        }, cts.Token);
 
        //注册一个委托：这个委托将在任务取消的时候调用
        cts.Token.Register(() =>
        {
            //在这个地方可以编写自己要处理的逻辑...
            Console.WriteLine($"任务取消，开始清理工作......{DateTime.Now.ToLongTimeString()}");
            Thread.Sleep(2000);
            Console.WriteLine($"任务取消，清理工作结束......{DateTime.Now.ToLongTimeString()}");
        });
 
        //这个地方肯定是有其他的逻辑来控制取消
        Thread.Sleep(3000);//模拟其他的耗时工作
        cts.Cancel();//取消任务
 
        /*
        子线程Id=3  22:12:52
        子线程Id=3  22:12:53
        子线程Id=3  22:12:53
        子线程Id=3  22:12:54
        子线程Id=3  22:12:54
        任务取消，开始清理工作......22:12:55
        子线程Id=3  22:12:55
        任务取消，清理工作结束......22:12:57
         */
    }
 
    //【3】Task任务延时自动取消：比如我们请求一个远程接口，如果长时间没有返回数据，我们可以做一个时间限制，超时可以取消任务（比如微信红包退回）
    static void Method10()
    {
        CancellationTokenSource cts = new CancellationTokenSource();
        // CancellationTokenSource cts = new CancellationTokenSource(3000);
        Task task = Task.Factory.StartNew(() =>
        {
            while (!cts.IsCancellationRequested)
            {
                Thread.Sleep(300);
 
                Console.WriteLine($"子线程Id={Thread.CurrentThread.ManagedThreadId}  {DateTime.Now.ToLongTimeString()}");
            }
        }, cts.Token);
 
        //注册一个委托：这个委托将在任务取消的时候调用
        cts.Token.Register(() =>
        {
            //在这个地方可以编写自己要处理的逻辑...
            Console.WriteLine($"任务取消，开始清理工作......{DateTime.Now.ToLongTimeString()}");
            Thread.Sleep(2000);
            Console.WriteLine($"任务取消，清理工作结束......{DateTime.Now.ToLongTimeString()}");
        });
 
        cts.CancelAfter(3000); //3秒后自动取消
 
        /*
        子线程Id=3  22:16:49
        子线程Id=3  22:16:50
        子线程Id=3  22:16:50
        子线程Id=3  22:16:50
        子线程Id=3  22:16:50
        子线程Id=3  22:16:51
        子线程Id=3  22:16:51
        子线程Id=3  22:16:51
        子线程Id=3  22:16:52
        任务取消，开始清理工作......22:16:52
        子线程Id=3  22:16:52
        任务取消，清理工作结束......22:16:54
         */
    }
 
    #endregion
 
    #region Task使用【5】Task中专门的异常处理：AggregateException
 
    //AggregateException:是一个异常集合，因为Task中可能抛出异常，所以我们需要新的类型来收集异常对象
    static void Method11()
    {
        var task = Task.Factory.StartNew(() =>
        {
            var childTask1 = Task.Factory.StartNew(() =>
            {
                //实际开发中这个地方写你处理的业务，可能会发生异常....
 
                //自己模拟一个异常
                throw new Exception("my god！Exception from childTask1 happend！");
            }, TaskCreationOptions.AttachedToParent);
 
            var childTask2 = Task.Factory.StartNew(() =>
            {
                throw new Exception("my god！Exception from childTask2 happend！");
            }, TaskCreationOptions.AttachedToParent);
        });
        try
        {
            try
            {
                task.Wait();   //1.异常抛出的时机(等待task执行完毕，这里是等到异常抛出）
            }
            catch (AggregateException ex)  //2.异常所在位置
            {
                foreach (var item in ex.InnerExceptions)
                {
                    Console.WriteLine(item.InnerException.Message + "     " + item.GetType().Name);
                }
 
                //3.异常集合，如果你想往上抛，需要使用Handle方法处理一下
                ex.Handle(p =>
                {
                    if (p.InnerException.Message == "my god！Exception from childTask1 happend！")
                        return true;//就结束了,不往上抛了
                    else
                        return false; //返回false表示往上继续抛出异常
                });
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("-----------------------------------------------------");
            Console.WriteLine(ex.InnerException.InnerException.Message);
        }
 
        /*
        my god！Exception from childTask2 happend！     AggregateException
        my god！Exception from childTask1 happend！     AggregateException
        -----------------------------------------------------
        my god！Exception from childTask2 happend！
         */
    }
 
    #endregion
 
    #region 监视锁：Lock  限制线程个数的一把锁
 
    //为什么要用锁？在多线程中，尤其是静态资源的访问，必然会有竞争
 
    private static int nums = 0;
    private static object myLock = new object();
    static void Method12()
    {
        for (int i = 0; i < 5; i++)
        {
            //开启5线程调用一个nums
            Task.Factory.StartNew(() =>
            {
                //TestMethod1();//不加锁的结果顺序是乱的，1,3,2,4,6,9，，，，500
                TestMethod2();//加锁的结果顺序是对的，因为把资源给锁住了，1,2,3,4,5,6，，，，500
            });
        }
    }
 
    static void TestMethod1()
    {
        for (int i = 0; i < 100; i++)
        {
            nums++;
            Console.WriteLine(nums);
        }
    }
 
    static void TestMethod2()
    {
        for (int i = 0; i < 100; i++)
        {
            lock (myLock)
            {
                nums++;
                Console.WriteLine(nums);
            }
        }
    }
 
    //Lock是Monitor语法糖，本质是解决资源的锁定问题
    //我们锁住的资源一定是让线程可访问到的，所以不能是局部变量。
    //锁住的资源千万不要是值类型。
    //lock也不能锁住string类型。
 
}
#endregion

2，Task中的跨线程访问控件和UI耗时任务卡顿的解决方法

//普通方法
      private void btnUpdate_Click(object sender, EventArgs e)
      {
          Task task = new Task(() =>
           {
               this.lblInfo.Text = "来自Task的数据更新：我们正在学习多线程！";
           });
          //task.Start();  //这样使用会报错
 
          //使用下面的方式解决报错的问题
          task.Start(TaskScheduler.FromCurrentSynchronizationContext());//使用任务调度器
 
      }
 
      //针对UI耗时的情况，单独重载其实并不是很好
      private void btnUpdate_Click1(object sender, EventArgs e)
      {
          Task task = new Task(() =>
          {
              //模拟耗时(这个地方会卡主)
              Thread.Sleep(5000);//界面会卡5秒钟，多线程不是万能，多线程并不是解决卡界面的。
              this.lblInfo.Text = "来自Task的数据更新：我们正在学习多线程！";
          });
          //task.Start();  //这样使用会报错
 
          //使用下面的方式解决报错的问题
          task.Start(TaskScheduler.FromCurrentSynchronizationContext());
      }
 
      //以后耗时任务都可以用这个方法
      //针对耗时任务，我们可以使用新的方法
      private void btnUpdate_Click2(object sender, EventArgs e)
      {
          this.btnUpdate.Enabled = false;
          this.lblInfo.Text = "数据更新中,请等待......";
          Task task =Task.Factory.StartNew(() =>
          {         
              Thread.Sleep(5000); //有耗时的任务，我们可以放到ThreadPool中          
          });
 
          //在ContinueWith中更新我们的数据
          task.ContinueWith(t =>
          {
              this.lblInfo.Text = "来自Task的数据更新：我们正在学习多线程！";
              this.btnUpdate.Enabled = true;
          },TaskScheduler.FromCurrentSynchronizationContext()); //更新操作到同步的上下文中        
      
      }

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：

using System;
using System.Threading;
using System.Threading.Tasks;
 
namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Task t = new Task(() =>
            {
                Console.WriteLine("任务开始工作……");
                //模拟工作过程
                Thread.Sleep(5000);
            });
            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的用法

2.1、创建任务
　　无返回值的方式
　　方式1:
　　var t1 = new Task(() => TaskMethod("Task 1"));
　　t1.Start();
　　

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

　　**方式2:**
　　```Task.Run(() => TaskMethod("Task 2"));```

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

```csharp
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"));
            //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);
        }
    }
}

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();
        }
    }
}

带返回值的方式
方式4:
　　Tasktask = 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");
            //该任务会运行在主线程中
            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");
            //等待任务的完成执行过程。
            getsumtask.Wait();
            //获得任务的执行结果
            Console.WriteLine("任务执行结果：{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}",
                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;
        }
    }
}

2.2、组合任务.ContinueWith
　　 简单Demo:

using System;
using System.Threading.Tasks;
 
namespace ConsoleApp1
{
    class Program
    {
        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();
        }
    }
}

任务的串行:

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);
 
            //t7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();
        }
    }
}

子任务:

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];
                //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。");
            //任务处理完成后执行的操作
            parent.ContinueWith(t =>
            {
                Array.ForEach(t.Result, r => Console.WriteLine(r));
            });
            //启动父任务
            parent.Start();
            //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
            //parent.Wait();
            Console.ReadLine();
 
        }
    }
}

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

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),
                                            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 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}",
                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("First task has been cancelled before execution");
            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("A task has been completed with result {0}.", longTask.Result);
        }
    }
}

2.4、处理任务中的异常
　　单个任务:

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}",
                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.WriteLine();
        }
    }
}

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}",
                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.WriteLine();
        }
    }
}

多个任务:

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}",
                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;
                });
            }
        }
    }
}

2.5、Task.FromResult的应用

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、使用IProgress实现异步编程的进程通知
　　IProgress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的实现类Progress的构造函数接收类型为Action的形参，通过这个委托让进度显示在UI界面中。

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()
        {
            //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();
        }
    }
}

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

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);
        }
 
        //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, "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);
 
        }
    }
}

不带回调方式的

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);
        }
 
        //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", "a delegate asynchronous call");
            task.ContinueWith(t => Console.WriteLine("Task is completed, 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);
 
        }
    }
}