关于c:c-Task

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1、Task 的劣势

ThreadPool 相比 Thread 来说具备了很多劣势，然而 ThreadPool 却又存在一些应用上的不不便。比方：
◆ ThreadPool 不反对线程的勾销、实现、失败告诉等交互性操作；
◆ ThreadPool 不反对线程执行的先后秩序；
以往，如果开发者要实现上述性能，须要实现很多额定的工作，当初，FCL 中提供了一个性能更弱小的概念：Task。Task 在线程池的根底上进行了优化，并提供了更多的 API。在 FCL4.0 中，如果咱们要编写多线程程序，Task 显然曾经优于传统的形式。
以下是一个简略的工作示例：

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {static void Main(string[] args)
        {Task t = new Task(() =>
            {Console.WriteLine("工作开始工作……");
                // 模仿工作过程
                Thread.Sleep(5000);
            });
            t.Start();
            t.ContinueWith((task) =>
            {Console.WriteLine("工作实现，实现时候的状态为：");
                Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}", task.IsCanceled, task.IsCompleted, task.IsFaulted);
            });
            Console.ReadKey();}
    }
}

2、Task 的用法

2.1、创立工作

（一）无返回值的形式
形式 1:

var t1 = new Task(() => TaskMethod("Task 1"));
  t1.Start();
  Task.WaitAll(t1);// 期待所有工作完结 
  注: 工作的状态:
  Start 之前为:Created
  Start 之后为:WaitingToRun

形式 2:

Task.Run(() => TaskMethod("Task 2"));

形式 3:

Task.Factory.StartNew(() => TaskMethod("Task 3")); 间接异步的办法 
  // 或者
  var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
  Task.WaitAll(t3);// 期待所有工作完结
  // 工作的状态:
  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"));
            // 标记为长时间运行工作, 则工作不会应用线程池, 而在独自的线程中运行。Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);

            #region 惯例的应用形式
            Console.WriteLine("主线程执行业务解决.");
            // 创立工作
            Task task = new Task(() =>
            {Console.WriteLine("应用 System.Threading.Tasks.Task 执行异步操作.");
                for (int i = 0; i < 10; i++)
                {Console.WriteLine(i);
                }
            });
            // 启动工作, 并安顿到当前任务队列线程中执行工作(System.Threading.Tasks.TaskScheduler)
            task.Start();
            Console.WriteLine("主线程执行其余解决");
            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 的实现形式:

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {async static void AsyncFunction()
        {await Task.Delay(1);
            Console.WriteLine("应用 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("主线程执行业务解决.");
            AsyncFunction();
            Console.WriteLine("主线程执行其余解决");
            for (int i = 0; i < 10; i++)
            {Console.WriteLine(string.Format("Main:i={0}", i));
            }
            Console.ReadLine();}
    }
}

（二）带返回值的形式
形式 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");
            // 该工作会运行在主线程中
            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 惯例应用形式
            // 创立工作
            Task<int> getsumtask = new Task<int>(() => Getsum());
            // 启动工作, 并安顿到当前任务队列线程中执行工作(System.Threading.Tasks.TaskScheduler)
            getsumtask.Start();
            Console.WriteLine("主线程执行其余解决");
            // 期待工作的实现执行过程。getsumtask.Wait();
            // 取得工作的执行后果
            Console.WriteLine("工作执行后果：{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("应用 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("主线程执行其余解决");
            for (int i = 1; i <= 3; i++)
                Console.WriteLine("Call Main()");
            int result = ret1.Result;                  // 阻塞主线程
            Console.WriteLine("工作执行后果：{0}", result);
        }

        async static Task<int> AsyncGetsum()
        {await Task.Delay(1);
            int sum = 0;
            Console.WriteLine("应用 Task 执行异步操作.");
            for (int i = 0; i < 100; i++)
            {sum += i;}
            return sum;
        }
    }
}

2.2、组合工作.ContinueWith

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {public static void Main()
        {
            // 创立一个工作
            Task<int> task = new Task<int>(() =>
            {
                int sum = 0;
                Console.WriteLine("应用 Task 执行异步操作.");
                for (int i = 0; i < 100; i++)
                {sum += i;}
                return sum;
            });
            // 启动工作, 并安顿到当前任务队列线程中执行工作(System.Threading.Tasks.TaskScheduler)
            task.Start();
            Console.WriteLine("主线程执行其余解决");
            // 工作实现时执行解决。Task cwt = task.ContinueWith(t =>
            {Console.WriteLine("工作实现后的执行后果：{0}", t.Result.ToString());
            });
            task.Wait();
            cwt.Wait();}
    }
}

工作的串行:

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);
            });

            // 期待 t2 和 t3 执行完
            Task.WaitAll(t2, t3);

            //t7 串行执行
            var t4 = Task.Factory.StartNew(() =>
            {Console.WriteLine("以后汇合元素个数：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
            });
            t4.Wait();}
    }
}
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];
                // 创立并启动子工作
                new Task(() => { result[0] = "我是子工作 1。"; }, TaskCreationOptions.AttachedToParent).Start();
                new Task(() => { result[1] = "我是子工作 2。"; }, TaskCreationOptions.AttachedToParent).Start();
                return result;
            }, "我是父工作，并在我的处理过程中创立多个子工作，所有子工作实现当前我才会完结执行。");
            // 工作解决实现后执行的操作
            parent.ContinueWith(t =>
            {Array.ForEach(t.Result, r => Console.WriteLine(r));
            });
            // 启动父工作
            parent.Start();
            // 期待工作完结 Wait 只能期待父线程完结, 没方法等到父线程的 ContinueWith 完结
            //parent.Wait();
            Console.ReadLine();}
    }
}

动静并行(TaskCreationOptions.AttachedToParent) 父工作期待所有子工作实现后 整个工作才算实现

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("以后节点的值为{0}; 解决的 ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
        }
    }
}

2.3、勾销工作 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、解决工作中的异样

单个工作:

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();}
    }
}

多个工作:

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 的形式:

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
            {
                // 异步的形式
                Task allTasks = Task.WhenAll(task1, task2, task3);
                await allTasks;
                // 同步的形式
                //Task.WaitAll(task1, task2, task3);
            }
            catch (NotImplementedException ex)
            {Console.WriteLine("task1 工作报错!");
            }
            catch (InvalidOperationException ex)
            {Console.WriteLine("task2 工作报错!");
            }
            catch (Exception ex)
            {Console.WriteLine("工作报错!");
            }

        }

        public static void Main()
        {Task task = ObserveOneExceptionAsync();
            Console.WriteLine("主线程持续运行........");
            task.Wait();}
    }
}

2.5、Task.FromResult 的利用

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、应用 IProgress 实现异步编程的过程告诉

IProgress<in T> 只提供了一个办法 void Report(T value)，通过 Report 办法把一个 T 类型的值报告给 IProgress, 而后 IProgress<in T> 的实现类 Progress<in T> 的构造函数接管类型为 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()
        {
            // 以后线程
            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("完结");
        }

        public static void Main()
        {Task task = Display();
            task.Wait();}
    }
}

2.7、Factory.FromAsync 的利用 (简 APM 模式 (委托) 转换为工作)(BeginXXX 和 EndXXX)

带回调形式的

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);

        }
    }
}

不带回调形式的

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);

        }
    }
}
//Task 启动带参数和返回值的函数工作
// 上面的例子 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 援用 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();}~~~~
正文完
c
发表至： c#
2021-01-21
 0
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