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不支持線程的取消、完成、失敗通知等交互性操作；
　　◆ ThreadPool不支持線程執行的先后次序；
　　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在線程池的基礎上進行了優化，并提供了更多的API。在FCL4.0中，如果我們要編寫多線程程序，Task顯然已經優于傳統的方式。
　　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、創建任務

　　（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:CreatedStart之后為:WaitingToRun

　　方式2:

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

　　方式3:

　　Task.Factory.StartNew(() => TaskMethod("Task 3")); 直接異步的方法 //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:RunningStart之后為: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"));//標記為長時間運行任務,則任務不會使用線程池,而在單獨的線程中運行。Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);#region 常規的使用方式Console.WriteLine("主線程執行業務處理.");//創建任務Task task = new Task(() =>{Console.WriteLine("使用System.Threading.Tasks.Task執行異步操作.");for (int i = 0; i < 10; i++){Console.WriteLine(i);}});//啟動任務,并安排到當前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)task.Start();Console.WriteLine("主線程執行其他處理");task.Wait();#endregionThread.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執行異步操作.");for (int i = 0; i < 10; i++){Console.WriteLine(string.Format("AsyncFunction:i={0}", i));}}public static void Main(){Console.WriteLine("主線程執行業務處理.");AsyncFunction();Console.WriteLine("主線程執行其他處理");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");//該任務會運行在主線程中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 常規使用方式//創建任務Task<int> getsumtask = new Task<int>(() => Getsum());//啟動任務,并安排到當前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)getsumtask.Start();Console.WriteLine("主線程執行其他處理");//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}",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執行異步操作.");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("主線程執行其他處理");for (int i = 1; i <= 3; i++)Console.WriteLine("Call Main()");int result = ret1.Result; //阻塞主線程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執行異步操作.");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(){//創建一個任務Task<int> task = new Task<int>(() =>{int sum = 0;Console.WriteLine("使用Task執行異步操作.");for (int i = 0; i < 100; i++){sum += i;}return sum;});//啟動任務,并安排到當前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)task.Start();Console.WriteLine("主線程執行其他處理");//任務完成時執行處理。Task cwt = task.ContinueWith(t =>{Console.WriteLine("任務完成后的執行結果：{0}", t.Result.ToString());});task.Wait();cwt.Wait();}} }

　　?任務的串行:

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并行執行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執行完Task.WaitAll(t2, t3);//t7串行執行var t4 = Task.Factory.StartNew(() =>{Console.WriteLine("當前集合元素個數：{0},Thread id {1}", 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];//創建并啟動子任務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，并在我的處理過程中創建多個子任務，所有子任務完成以后我才會結束執行。");//任務處理完成后執行的操作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只能等待父線程結束,沒辦法等到父線程的ContinueWith結束//parent.Wait();Console.ReadLine();}} }

　　動態并行(TaskCreationOptions.AttachedToParent) 父任務等待所有子任務完成后 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),CancellationToken.None,TaskCreationOptions.AttachedToParent,TaskScheduler.Default);if (current.Right != null)Task.Factory.StartNew(() => DisplayNode(current.Right),CancellationToken.None,TaskCreationOptions.AttachedToParent,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}",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、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}",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}",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;});}}} }

? ? 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{//異步的方式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("主線程繼續運行........");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("主程序繼續執行。。。。");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實現異步編程的進程通知

　　IProgress<in T>只提供了一個方法void Report(T value)，通過Report方法把一個T類型的值報告給IProgress,然后IProgress<in T>的實現類Progress<in T>的構造函數接收類型為Action<T>的形參，通過這個委托讓進度顯示在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(){//當前線程var progress = new Progress<int>(percent =>{Console.Clear();Console.Write("{0}%", percent);});//線程池線程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(委托)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.ContinueWithstatic 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.IsThreadPoolThread);Thread.Sleep(TimeSpan.FromSeconds(2));Thread.CurrentThread.Name = threadName;return string.Format("Thread name: {0}", Thread.CurrentThread.Name);}//執行的流程是 先執行Test--->task.ContinueWithstatic 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);}} }

---

//Task啟動帶參數和返回值的函數任務 //下面的例子test2 是個帶參數和返回值的函數。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; }//測試調用 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); }//= 下載網站源文件例子 == == == == == == == == == == == == //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));//相當于//Thread th= new Thread(new ThreadStart(test2));//th.Start(); }

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