c#中Task线程的用法

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

　　（一）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:CreatedStart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//任务的状态:Start之前为:RunningStart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();#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();}}
}

　　（二）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;}}
}

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<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;}}
}

　　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();}}
}

　　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;});}}}
}

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<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<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();}}
}

　　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.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.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启动带参数和返回值的函数任务
//下面的例子test2 是个带参数和返回值的函数。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;
}//测试调用
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);
}//= 下载网站源文件例子 == == == == == == == == == == == ==
//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));//相当于//Thread th= new Thread(new ThreadStart(test2));//th.Start();
}