发布：2019/10/16 22:49:19作者：管理员来源：本站浏览次数：1009

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。

    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.创建任务

    class Program
    { static void Main(string[] args)
        { //创建任务 多种方式 //方式1  var t1 = new Task(() => TaskMethod("Task 1"));
            Console.WriteLine($"t1任务状态:{t1.Status}");
            t1.Start();
            Console.WriteLine($"t1任务状态:{t1.Status}");
            Task.WaitAll(t1);//等待所有任务结束  Console.WriteLine($"t1任务状态:{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")); //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);
        }
    }

2.1 async/await的实现方式

无返回值

    class Program
    { 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(($"Main:i={i}"));
            }
            Console.ReadLine();
        } async static void AsyncFunction()
        { await Task.Delay(1);
            Console.WriteLine("使用System.Threading.Tasks.Task执行异步操作."); for (int i = 0; i < 10; i++)
            {
                Console.WriteLine($"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"); //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);
            Console.ReadLine(); #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());
            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执行异步操作."); for (int i = 0; i < 100; i++)
            {
                sum += i;
            } return sum;
        }
    }

阻塞主线程，等待返回结果

    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);
            Console.ReadLine();
        } static async 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;
        }
    }

3.组合任务 ContinueWith

    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.ContinueWith(t => {
                Console.WriteLine("任务完成后的执行结果：{0}", t.Result.ToString());
            });
            Console.ReadLine();
        }
    }

任务的串行

    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并行执行 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并行执行 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();
            Console.ReadLine();
        }
    }

子任务

  class Program
    { static void Main(string[] args)
        {
            WaitForSimpleNestedTask();
            Console.WriteLine("=====================================================");
            SimpleNestedTask();
            Thread.SpinWait(600000);//等待SimpleNestedTask结束 再运行 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;
                }); // 父任务等待子任务完成 return nested.Result;
            }); //输出的时候使用了返回值outer.Result，所以自动等待父任务完成 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.");
                });
            }); //等待父任务完成，再输出字符串，如果没有这个等待，这句话会先输出  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); //增加参数TaskCreationOptions.AttachedToParent，将子任务附加进父任务，这样子任务完成后，父任务才算完成。  }); //等待父任务完成，再输出字符串，如果没有这个等待，这句话会先输出  parent.Wait();
            Console.WriteLine("Outer has completed.");
        }
    }

动态并行,父任务等待所有子任务完成后整个任务才算完成

  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("当前节点的值为{0};处理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
        }
    }

取消任务 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.处理任务中的异常

单个任务

    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();
        }
    }

多个任务

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 { //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();
            Console.ReadLine();
        }
    }

5.Task.FromResult的应用

    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("主程序继续执行。。。。"); string result = task.Result;
            Console.WriteLine("result={0}", result);
            Console.ReadLine();
        } private static Task<string> GetValueFromCache(string key)
        {
            Console.WriteLine("GetValueFromCache开始执行。。。。");
            Thread.Sleep(5000);
            Console.WriteLine("GetValueFromCache继续执行。。。。"); if (cache.TryGetValue(key, out var result))
            { return Task.FromResult(result);
            } return Task.FromResult("");
        }

    }

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

    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()
        { //当前线程 var progress = new Progress<int>(percent => {
                Console.Clear();
                Console.Write($"{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();
        }
    }

7.Factory.FromAsync的应用 (简APM模式(委托)转换为任务)(BeginXXX和EndXXX)

带回调方式的带回调方式的

    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);
        } //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);
            Console.ReadLine();
        }
    }

不带回调方式的

    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);
        } //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);
            Console.ReadLine();
        }
    }

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C#多线程服务，控制最大线程并发和最小线程并发　

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