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();

　　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);        }    }}

　　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:

　　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
      
        CreateTask(string name)        {            return new Task
       
        (() => TaskMethod(name));        }        static void Main(string[] args)        {            TaskMethod("Main Thread Task");            Task
        
          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
         
           getsumtask = new Task
          
           (() => 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;        }    }}
          
         
        
       
      

    async/await的实现:

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

　　2.2、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
      
        task = new Task
       
        (() =>            {                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
      
        stack = new ConcurrentStack
       
        ();            //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
      
        parent = new Task
       
        (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
      
       (() => 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
       
        (() => 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
      
        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
      
       (() => TaskMethod("Task 3", 3));                var t2 = new Task
       
        (() => 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            {                //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();        }    }}

　　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
      
        cache = new Dictionary
       
        ()        {            {
     "0001","A"},            {
     "0002","B"},            {
     "0003","C"},            {
     "0004","D"},            {
     "0005","E"},            {
     "0006","F"},        };        public static void Main()        {            Task
        
          task = GetValueFromCache("0006");            Console.WriteLine("主程序继续执行。。。。");            string result = task.Result;            Console.WriteLine("result={0}", result);        }        private static Task
         
           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<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
      
        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
       
        (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
      
        task = Task
       
        .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
      
        task = Task
       
        .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);        }    }}