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} IsCompleted={1} IsFaulted={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<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.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); } } }