C# Task的使用

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後次序；
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，並提供了更多的API。在FCL4.0中，如果我們要編寫多線程程序，Task顯然已經優於傳統的方式。

    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，完成時候的狀態爲：");
                Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}", task.IsCanceled, task.IsCompleted, task.IsFaulted);
            });
            Console.ReadKey();
        }
    }

2.創建任務

    class Program
    {
        static void Main(string[] args)
        {
            //創建任務 多種方式
            //方式1  
            var t1 = new Task(() => TaskMethod("Task 1"));
            Console.WriteLine($"t1任務狀態:{t1.Status}");
            t1.Start();
            Console.WriteLine($"t1任務狀態:{t1.Status}");
            Task.WaitAll(t1);//等待所有任務結束 
            Console.WriteLine($"t1任務狀態:{t1.Status}");
            Console.ReadKey();
            //方式2
            Task.Run(() => TaskMethod("Task 2"));
            //方式3 
            Task.Factory.StartNew(() => Console.WriteLine("Task 3")); 
        }

        static void TaskMethod(string str)
        {
            Thread.Sleep(1000);
            Console.WriteLine(str);
        }
    }

    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"));
            //標記爲長時間運行任務,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);
                }
            });
            //啓動任務,並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();
            #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);
        }
    }

2.1 async/await的實現方式

無返回值

    class Program
    {
        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(($"Main:i={i}"));
            }
            Console.ReadLine();
        }
        async static void AsyncFunction()
        {
            await Task.Delay(1);
            Console.WriteLine("使用System.Threading.Tasks.Task執行異步操作.");
            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine($"AsyncFunction:i={i}");
            }
        }
    }

 

有返回值

 class Program
    {
        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);
            Console.ReadLine();

            #region 常規使用方式
            //創建任務
            Task<int> getsumtask = new Task<int>(() => Getsum());
            //啓動任務,並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());
            Console.ReadLine();
            #endregion
        }

        static Task<int> CreateTask(string name)
        {
            return new Task<int>(() => TaskMethod(name));
        }

        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;
        }
    }

 

阻塞主線程，等待返回結果

    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);
            Console.ReadLine();
        }

        static async 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;
        }
    }

3.組合任務 ContinueWith

    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;
            });
            //啓動任務,並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.ContinueWith(t =>
            {
                Console.WriteLine("任務完成後的執行結果：{0}", t.Result.ToString());
            });
            Console.ReadLine();
        }
    }

 

任務的串行

    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並行執行
            var t2 = t1.ContinueWith(t =>
            {
                stack.TryPop(out var result);
                Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
            });

            //t2,t3並行執行
            var t3 = t1.ContinueWith(t =>
            {
                stack.TryPop(out var 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();
            Console.ReadLine();
        }
    }

 

子任務

  class Program
    {
        static void Main(string[] args)
        {
            WaitForSimpleNestedTask();
            Console.WriteLine("=====================================================");
            SimpleNestedTask();
            Thread.SpinWait(600000);//等待SimpleNestedTask結束 再運行
            Console.WriteLine("=====================================================");
            SimpleNestedTaskAttachedToParent();
            Console.Read();
        }
        static void WaitForSimpleNestedTask()
        {
            var outer = Task<int>.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer1 task executing.");

                var nested = Task<int>.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested1 task starting.");
                    Thread.SpinWait(5000000);
                    Console.WriteLine("Nested1 task completing.");
                    return 42;
                });

                // 父任務等待子任務完成
                return nested.Result;
            });
            //輸出的時候使用了返回值outer.Result，所以自動等待父任務完成
            Console.WriteLine("Outer1 has returned {0}.", outer.Result);
        }
        static void SimpleNestedTask()
        {
            var parent = Task.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer2 task executing.");

                var child = Task.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested2 task starting.");
                    Thread.SpinWait(500000);
                    Console.WriteLine("Nested2 task completing.");
                });
            });
            //等待父任務完成，再輸出字符串，如果沒有這個等待，這句話會先輸出
            parent.Wait();
            Console.WriteLine("Outer2 has completed.");
        }

        static void SimpleNestedTaskAttachedToParent()
        {
            var parent = Task.Factory.StartNew(() =>
            {
                Console.WriteLine("Outer3 task executing.");

                var child = Task.Factory.StartNew(() =>
                {
                    Console.WriteLine("Nested3 task starting.");
                    Thread.SpinWait(500000);
                    Console.WriteLine("Nested3 task completing.");
                }, TaskCreationOptions.AttachedToParent);
                //增加參數TaskCreationOptions.AttachedToParent，將子任務附加進父任務，這樣子任務完成後，父任務纔算完成。
            });

            //等待父任務完成，再輸出字符串，如果沒有這個等待，這句話會先輸出
            parent.Wait();
            Console.WriteLine("Outer has completed.");
        }
    }

動態並行,父任務等待所有子任務完成後 整個任務纔算完成

  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);
            Console.ReadLine();
        }

        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("當前節點的值爲{0};處理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
        }
    }

取消任務 CancellationTokenSource

   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);
            Console.ReadLine();
        }
    }

4.處理任務中的異常

單個任務

    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.ReadLine();
        }
    }

多個任務

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)
            {
                // enumerate the exceptions that have been aggregated
                foreach (Exception inner in ex.InnerExceptions)
                {
                    Console.WriteLine($"Exception type {inner.GetType()} from {inner.Source} {ex.Message}");
                }
            }
            Console.ReadLine();
            Console.WriteLine("----------------------");
        }
    }

 

async/await的方式

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();
            Console.ReadLine();
        }
    }

 

5.Task.FromResult的應用

    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);
            Console.ReadLine();
        }

        private static Task<string> GetValueFromCache(string key)
        {
            Console.WriteLine("GetValueFromCache開始執行。。。。");
            Thread.Sleep(5000);
            Console.WriteLine("GetValueFromCache繼續執行。。。。");
            if (cache.TryGetValue(key, out var result))
            {
                return Task.FromResult(result);
            }
            return Task.FromResult("");
        }

    }

 

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,然後IProgress<in T>的實現類Progress<in T>的構造函數接收類型爲Action<T>的形參，通過這個委託讓進度顯示在UI界面中

    class Program
    {
        static void DoProcessing(IProgress<int> progress)
        {
            for (int i = 0; i <= 100; ++i)
            {
                Thread.Sleep(100);
                progress?.Report(i);
            }
        }

        static async Task Display()
        {
            //當前線程
            var progress = new Progress<int>(percent =>
            {
                Console.Clear();
                Console.Write($"{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();
        }
    }

 

7.Factory.FromAsync的應用 (簡APM模式(委託)轉換爲任務)(BeginXXX和EndXXX)

帶回調方式的帶回調方式的

    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.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);
            Console.ReadLine();
        }
    }

 

不帶回調方式的

    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(2000);
            Thread.CurrentThread.Name = threadName;
            return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
        }

        //執行的流程是 先執行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);
            Console.ReadLine();
        }
    }