C#线程学习笔记七：Task详细用法

一、Task类简介：

Task类是在.NET Framework 4.0中提供的新功能，主要用于异步操作的控制。它比Thread和ThreadPool提供了更为强大的功能，并且更方便使用。

Task和Task<TResult>类：前者接收的是Action委托类型；后者接收的是Func<TResult>委托类型。

任务Task和线程Thread的区别：

1、任务是架构在线程之上。也就是说任务最终还是要抛给线程去执行，它们都是在同一命名空间System.Threading下。

2、任务跟线程并不是一对一的关系。比如说开启10个任务并不一定会开启10个线程，因为使用Task开启新任务时，是从线程池中调用线程，这点与

ThreadPool.QueueUserWorkItem类似。

    二、Task的创建

    2.1创建方式1：调用构造函数

    class Program
    {
        static void Main(string[] args)
        {
            #region 工作者线程：使用任务实现异步
            ThreadPool.SetMaxThreads(, );
            PrintMessage("Main thread start.");
            //调用构造函数创建Task对象
            Task<int> task = new Task<int>(n => AsyncMethod((int)n), );

            //启动任务
            task.Start();
            //等待任务完成
            task.Wait();
            Console.WriteLine("The method result is: " + task.Result);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// 打印线程池信息
        /// </summary>
        /// <param name="data"></param>
        private static void PrintMessage(string data)
        {
            //获得线程池中可用的工作者线程数量及I/O线程数量
            ThreadPool.GetAvailableThreads(out int workThreadNumber, out int ioThreadNumber);

            Console.WriteLine("{0}\n CurrentThreadId is:{1}\n CurrentThread is background:{2}\n WorkerThreadNumber is:{3}\n IOThreadNumbers is:{4}\n",
                data,
                Thread.CurrentThread.ManagedThreadId,
                Thread.CurrentThread.IsBackground.ToString(),
                workThreadNumber.ToString(),
                ioThreadNumber.ToString());
        }

        /// <summary>
        /// 异步方法
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        private static int AsyncMethod(int n)
        {
            Thread.Sleep();
            PrintMessage("Asynchoronous method.");

            int sum = ;
            for (int i = ; i < n; i++)
            {
                //运算溢出检查
                checked
                {
                    sum += i;
                }
            }

            return sum;
        }
    }

2.2创建方式2：任务工厂

    class Program
    {
        static void Main(string[] args)
        {
            #region 工作者线程：使用任务工厂实现异步
            ////无参无返回值
            //ThreadPool.SetMaxThreads(1000, 1000);
            //Task.Factory.StartNew(() => PrintMessage("Main thread."));
            //Console.Read();

            //有参有返回值
            ThreadPool.SetMaxThreads(, );
            PrintMessage("Main thread start.");
            var task = Task.Factory.StartNew(n => AsyncMethod((int)n), );
            //等待任务完成
            task.Wait();
            Console.WriteLine("The method result is: " + task.Result);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// 打印线程池信息
        /// </summary>
        /// <param name="data"></param>
        private static void PrintMessage(string data)
        {
            //获得线程池中可用的工作者线程数量及I/O线程数量
            ThreadPool.GetAvailableThreads(out int workThreadNumber, out int ioThreadNumber);

            Console.WriteLine("{0}\n CurrentThreadId is:{1}\n CurrentThread is background:{2}\n WorkerThreadNumber is:{3}\n IOThreadNumbers is:{4}\n",
                data,
                Thread.CurrentThread.ManagedThreadId,
                Thread.CurrentThread.IsBackground.ToString(),
                workThreadNumber.ToString(),
                ioThreadNumber.ToString());
        }

        /// <summary>
        /// 异步方法
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        private static int AsyncMethod(int n)
        {
            Thread.Sleep();
            PrintMessage("Asynchoronous method.");

            int sum = ;
            for (int i = ; i < n; i++)
            {
                //运算溢出检查
                checked
                {
                    sum += i;
                }
            }

            return sum;
        }
    }

2.3创建方式3：Run方法

    class Program
    {
        static void Main(string[] args)
        {
            #region 工作者线程：使用Task.Run实现异步
            ThreadPool.SetMaxThreads(, );
            PrintMessage("Main thread start.");
            var task = Task.Run(() => AsyncMethod());
            //等待任务完成
            task.Wait();
            Console.WriteLine("The method result is: " + task.Result);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// 打印线程池信息
        /// </summary>
        /// <param name="data"></param>
        private static void PrintMessage(string data)
        {
            //获得线程池中可用的工作者线程数量及I/O线程数量
            ThreadPool.GetAvailableThreads(out int workThreadNumber, out int ioThreadNumber);

            Console.WriteLine("{0}\n CurrentThreadId is:{1}\n CurrentThread is background:{2}\n WorkerThreadNumber is:{3}\n IOThreadNumbers is:{4}\n",
                data,
                Thread.CurrentThread.ManagedThreadId,
                Thread.CurrentThread.IsBackground.ToString(),
                workThreadNumber.ToString(),
                ioThreadNumber.ToString());
        }

        /// <summary>
        /// 异步方法
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        private static int AsyncMethod(int n)
        {
            Thread.Sleep();
            PrintMessage("Asynchoronous method.");

            int sum = ;
            for (int i = ; i < n; i++)
            {
                //运算溢出检查
                checked
                {
                    sum += i;
                }
            }

            return sum;
        }
    }

三、Task的简略生命周期

    可通过Status属性获取。

状态	说明
Created	表示默认初始化任务，但是工厂及Run创建方式会直接跳过。
WaitingToRun	表示等待任务调度器分配线程给任务执行。
RanToCompletion	表示任务执行完毕。

    四、Task的控制

方法名	说明
Task.Wait	如task1.Wait();就是等待task1任务的执行，执行完成后状态变为Completed。
Task.WaitAll	等待所有的任务执行完毕。
Task.WaitAny	等待任意一个任务完成后就继续向下执行。
Task.ContinueWith	上一个任务执行完成后自动启动下一个任务，实现任务的按序进行。
CancellationTokenSource	通过其token来取消一个Task。

    4.1、组合任务

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：Task组合任务
            //创建一个任务
            Task<int> task = new Task<int>(() =>
            {
                int sum = ;
                Console.WriteLine("使用任务实现异步。");
                for (int i = ; i < ; i++)
                {
                    sum += i;
                }
                return sum;
            });
            //任务启动并安排到任务队列等待执行(System.Threading.Tasks.TaskScheduler)
            task.Start();
            //任务完成时执行处理
            Task cwt = task.ContinueWith(t =>
            {
                Console.WriteLine("任务的执行结果：{0}", t.Result.ToString());
            });
            task.Wait();
            cwt.Wait();
            Console.ReadLine();
            #endregion
        }
    }

运行结果如下：

4.2、串行任务

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：Task串行任务
            //堆栈
            ConcurrentStack<int> stack = new ConcurrentStack<int>();

            //t1最早串行
            var t1 = Task.Factory.StartNew(() =>
            {
                stack.Push();
                stack.Push();
            });

            //t2、t3并行执行
            var t2 = t1.ContinueWith(t =>
            {
                stack.TryPop(out int result);
                Console.WriteLine("Task t2 result={0},thread id is {1}.", result, Thread.CurrentThread.ManagedThreadId);
            });
            var t3 = t1.ContinueWith(t =>
            {
                stack.TryPop(out int result);
                Console.WriteLine("Task t3 result={0},thread id is {1}.", result, Thread.CurrentThread.ManagedThreadId);
            });

            //等待t2、t3执行完毕
            Task.WaitAll(t2, t3);

            //t4串行执行
            var t4 = Task.Factory.StartNew(() =>
            {
                Console.WriteLine("The stack count={0},thread id is {1}.", stack.Count, Thread.CurrentThread.ManagedThreadId);
            });
            t4.Wait();

            Console.ReadLine();
            #endregion
        }
    }

运行结果如下：

4.3、子任务

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：Task子任务
            Task<string[]> parent = new Task<string[]>(state =>
            {
                Console.WriteLine(state);
                string[] result = new string[];
                //创建并启动子任务
                new Task(() => { result[] = "子任务1。"; }, TaskCreationOptions.AttachedToParent).Start();
                new Task(() => { result[] = "子任务2。"; }, TaskCreationOptions.AttachedToParent).Start();
                return result;
            }, "我是父任务，我创建了2个子任务，它们执行完后我才会结束执行。");
            //任务完成时执行处理
            parent.ContinueWith(t =>
            {
                Array.ForEach(t.Result, r => Console.WriteLine(r));
            });
            //启动父任务
            parent.Start();
            parent.Wait();
            Console.ReadLine();
            #endregion
        }
    }

运行结果如下：

4.4、动态并行任务

    /// <summary>
    /// 结点类
    /// </summary>
    class Node
    {
        public Node Left { get; set; }
        public Node Right { get; set; }
        public string Text { get; set; }
    }

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：Task动态并行任务
            Node root = GetNode();
            DisplayTree(root);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// GetNode方法
        /// </summary>
        /// <returns></returns>
        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;
        }

        /// <summary>
        /// DisplayTree方法
        /// </summary>
        /// <param name="root"></param>
        static void DisplayTree(Node root)
        {
            var task = Task.Factory.StartNew
                (
                    () =>
                    DisplayNode(root),
                    CancellationToken.None,
                    TaskCreationOptions.None,
                    TaskScheduler.Default
                );
            task.Wait();
        }

        /// <summary>
        /// DisplayNode方法
        /// </summary>
        /// <param name="current"></param>
        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("The current node text={0},thread id is {1}.", current.Text, Thread.CurrentThread.ManagedThreadId);
            }
        }
    }

运行结果如下：

4.5、取消任务

    class Program
    {
        static void Main(string[] args)
        {
            #region 取消任务
            ThreadPool.SetMaxThreads(, );
            PrintMessage("Main thread start.");
            CancellationTokenSource cts = new CancellationTokenSource();

            //调用构造函数创建Task对象，将一个CancellationToken传给Task构造器从而使Task和CancellationToken关联起来。
            Task<int> task = new Task<int>(n => AsyncMethod(cts.Token, (int)n), );

            //启动任务
            task.Start();
            //延迟取消任务
            Thread.Sleep();

            //取消任务
            cts.Cancel();
            Console.WriteLine("The method result is: " + task.Result);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// 打印线程池信息
        /// </summary>
        /// <param name="data"></param>
        private static void PrintMessage(string data)
        {
            //获得线程池中可用的工作者线程数量及I/O线程数量
            ThreadPool.GetAvailableThreads(out int workThreadNumber, out int ioThreadNumber);

            Console.WriteLine("{0}\n CurrentThreadId is:{1}\n CurrentThread is background:{2}\n WorkerThreadNumber is:{3}\n IOThreadNumbers is:{4}\n",
                data,
                Thread.CurrentThread.ManagedThreadId,
                Thread.CurrentThread.IsBackground.ToString(),
                workThreadNumber.ToString(),
                ioThreadNumber.ToString());
        }

        /// <summary>
        /// 异步方法
        /// </summary>
        /// <param name="ct"></param>
        /// <param name="n"></param>
        /// <returns></returns>
        private static int AsyncMethod(CancellationToken ct, int n)
        {
            Thread.Sleep();
            PrintMessage("Asynchoronous method.");

            int sum = ;
            try
            {
                for (int i = ; i < n; i++)
                {
                    //当CancellationTokenSource对象调用Cancel方法时，就会引起OperationCanceledException异常，
                    //通过调用CancellationToken的ThrowIfCancellationRequested方法来定时检查操作是否已经取消，
                    //这个方法和CancellationToken的IsCancellationRequested属性类似。
                    ct.ThrowIfCancellationRequested();
                    Thread.Sleep();
                    //运算溢出检查
                    checked
                    {
                        sum += i;
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception is:" + e.GetType().Name);
                Console.WriteLine("Operation is canceled.");
            }

            return sum;
        }
    }

运行结果如下：

4.6、处理单个任务中的异常

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：处理单个任务中的异常
            try
            {
                Task<int> task = Task.Run(() => SingleTaskExceptionMethod("Single task.", ));
                int result = task.GetAwaiter().GetResult();
                Console.WriteLine("Result:{0}", result);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Single task exception caught:{0}", ex.Message);
            }
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// SingleTaskException方法
        /// </summary>
        /// <param name="name"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        static int SingleTaskExceptionMethod(string name, int seconds)
        {
            Console.WriteLine("Task {0} is running on thread {1}.Is it threadpool thread?:{2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(seconds));
            throw new Exception("Boom.");
        }
    }

运行结果如下：

4.7、处理多个任务中的异常

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：处理多个任务中的异常
            try
            {
                var t1 = new Task<int>(() => MultipleTaskExceptionMethod("Multiple task 1", ));
                var t2 = new Task<int>(() => MultipleTaskExceptionMethod("Multiple task 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);
                Console.ReadLine();
            }
            catch (AggregateException ex)
            {
                ex.Handle
                    (
                        exception =>
                        {
                            Console.WriteLine(exception.Message);
                            return true;
                        }
                    );
            }
            #endregion
        }

        /// <summary>
        /// MultipleTaskException方法
        /// </summary>
        /// <param name="name"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        static int MultipleTaskExceptionMethod(string name, int seconds)
        {
            Console.WriteLine("Task {0} is running on thread id {1}. Is it threadpool thread?:{2}",
                name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(seconds));
            throw new Exception(string.Format("Task {0} Boom.", name));
        }
    }

运行结果如下：

4.8、Task.FromResult的应用

    class Program
    {
        //字典
        private static readonly IDictionary<string, string> cache = new Dictionary<string, string>()
        {
            {"","A"},
            {"","B"},
            {"","C"},
            {"","D"},
            {"","E"},
            {"","F"},
        };

        public static void Main()
        {
            #region 工作者线程：Task.FromResult的应用
            Task<string> task = GetValueFromCacheMethod("");
            Console.WriteLine("Result={0}", task.Result.ToString());
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// GetValueFromCache方法
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        private static Task<string> GetValueFromCacheMethod(string key)
        {
            Console.WriteLine("GetValueFromCache开始执行……");
            string result = string.Empty;
            Thread.Sleep();
            Console.WriteLine("GetValueFromCache继续执行……");
            if (cache.TryGetValue(key, out result))
            {
                return Task.FromResult(result);
            }
            return Task.FromResult("");
        }
    }

运行结果如下：

4.9、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。

    class Program
    {
        public static void Main()
        {
            #region 工作者线程：使用IProgress实现异步编程的进程通知
            Task task = Display();
            task.Wait();
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// DoProcessing方法
        /// </summary>
        /// <param name="progress"></param>
        static void DoProcessing(IProgress<int> progress)
        {
            for (int i = ; i <= ; i++)
            {
                Thread.Sleep();
                if (progress != null)
                {
                    progress.Report(i);
                }
            }
        }

        /// <summary>
        /// Display方法
        /// </summary>
        /// <returns></returns>
        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");
        }
    }

运行结果如下：

4.10、Factory.FromAsync的应用

(简APM模式(委托)转换为任务)(BeginXXX和EndXXX)

带回调方式：

    class Program
    {
        //使用委托实现异步，是使用了异步编程模型APM。
        private delegate string AsynchronousTask(string threadName);

        public static void Main()
        {
            #region 工作者线程：带回调方式的Factory.FromAsync的应用
            AsynchronousTask d = TestMethod;
            Console.WriteLine("Option 1");
            Task<string> task = Task<string>.Factory.FromAsync(d.BeginInvoke("AsyncTaskThread", Callback, "A delegate asynchronous called."), 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);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// FromAsync方法
        /// </summary>
        /// <param name="threadName"></param>
        /// <returns></returns>
        private static string FromAsyncMethod(string threadName)
        {
            Console.WriteLine("Starting...");
            Console.WriteLine("Is it threadpool thread?:{0}", Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds());
            Thread.CurrentThread.Name = threadName;
            return string.Format("Thread name:{0}", Thread.CurrentThread.Name);
        }

        /// <summary>
        /// Callback方法
        /// </summary>
        /// <param name="ar"></param>
        private static void Callback(IAsyncResult ar)
        {
            Console.WriteLine("Starting a callback...");
            Console.WriteLine("State passed to a callbak: {0}", ar.AsyncState);
            Console.WriteLine("Is it threadpool thread?:{0}", Thread.CurrentThread.IsThreadPoolThread);
            Console.WriteLine("Threadpool worker thread id: {0}",Thread.CurrentThread.ManagedThreadId);
        }
    }

运行结果如下：

不带回调方式：

    class Program
    {
        //使用委托实现异步，是使用了异步编程模型APM。
        private delegate string AsynchronousTask(string threadName);

        public static void Main()
        {
            #region 工作者线程：不带回调方式的Factory.FromAsync的应用
            AsynchronousTask d = FromAsyncMethod;
            Task<string> task = Task<string>.Factory.FromAsync(d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "A delegate asynchronous called.");
            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);
            Console.ReadLine();
            #endregion
        }

        /// <summary>
        /// FromAsync方法
        /// </summary>
        /// <param name="threadName"></param>
        /// <returns></returns>
        private static string FromAsyncMethod(string threadName)
        {
            Console.WriteLine("Starting...");
            Console.WriteLine("Is it threadpool thread?:{0}", Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds());
            Thread.CurrentThread.Name = threadName;
            return string.Format("Thread name:{0}", Thread.CurrentThread.Name);
        }
    }

运行结果如下：

参考自：

https://www.cnblogs.com/kelelipeng/p/10237669.html

https://www.cnblogs.com/lonelyxmas/p/9509298.html