C# Task用法

匿名 (未验证) 提交于 2019-12-02 22:06:11

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();         }     } }
Program

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();
  Task.WaitAll(t1);//等待所有任务结束
  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

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);         }     } }
Program

  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();         }     } }
Program

  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");             //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;         }     } }
Program

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;         }     } }
Program

  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();         }     } }
Program

   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();         }     } }
Program

  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();          }     } }
Program

  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);         }     } }
Program

  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);         }     } }
Program

  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();         }     } }
Program

  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;                 });             }         }     } }
Program

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             {                 //异步的方式                 Task allTasks = Task.WhenAll(task1, task2, task3);                 await allTasks;                 //同步的方式                 //Task.WaitAll(task1, task2, task3);             }             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();         }     } }
Program

  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("");         }      } }
Program

  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。

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();         }     } }
Program

  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);          }     } }
Program

  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);          }     } }
Program

文章来源: C# Task用法

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