Net CRL via (C#)高级进阶——多线程（计算限制的异步操作篇）

执行简单的计算限制操作+限制执行上下文流动：

public static void UseThreadPool()
        {
            CallContext.LogicalSetData("Data", 2);//存在当前线程的资源
            ThreadPool.QueueUserWorkItem(
                state => Console.WriteLine("Name1={0}", CallContext.LogicalGetData("Data")));

            ExecutionContext.SuppressFlow();//取消了上下文的流动 无法异步操作无法获得当前资源


            ThreadPool.QueueUserWorkItem(ComputeBoundOp, CallContext.LogicalGetData("Data"));//这样的写法无效，委托的参数已经在当前线程复制一份传进去了。

            ThreadPool.QueueUserWorkItem(
                state => Console.WriteLine("Name2={0}",CallContext.LogicalGetData("Data")));

            ExecutionContext.RestoreFlow();//恢复上下文流动

            ThreadPool.QueueUserWorkItem(
                state => Console.WriteLine("Name3={0}", CallContext.LogicalGetData("Data")));
            //ThreadPool.QueueUserWorkItem(ComputeBoundOp, CallContext.LogicalGetData("Data"));

            //for (int i=0;i<5;i++)
            //{
            //    ThreadPool.QueueUserWorkItem(ComputeBoundOp,CallContext.LogicalGetData("Data"));
            //    Console.WriteLine("doing other work");
            //    Thread.Sleep(1000);
            //}
        }

        private static void ComputeBoundOp(object state)
        {
            Console.WriteLine("ComputeBoundOp:state={0}", state);
            Thread.Sleep(1000);
        }

协作式取消和超时：

        /// <summary>
        /// 当前线程取消异步操作
        /// </summary>
        private static void CancellationDemo()
        {
            CancellationTokenSource cts = new CancellationTokenSource();

            ThreadPool.QueueUserWorkItem(o => Count(cts.Token, 1000));
            Console.WriteLine("Press <Enter> to cancel the operation.");
            Console.ReadLine();
            cts.Cancel();
        }
        private static void Count(CancellationToken token,int countTO)
        {
            for(int count=0;count<countTO;count++)
            {
                if(token.IsCancellationRequested)
                {
                    Console.WriteLine("Count is cancelled");
                    break;
                }
                Console.WriteLine(count);
                Thread.Sleep(200);
            }
        }

任务取消时回调

/// <summary>
        /// 任务取消后回调register方法。
        /// </summary>
        private static void CancellationTS_Register()
        {
            var cts = new CancellationTokenSource();
            //bool useSynchronizationContext 指明是否使用调用线程SynchronizationContext来调用委托
            //否则调用Cancel的线程会顺序调用所有方法。
            cts.Token.Register(() => Console.WriteLine("Canceled 1,ThreadId "+Thread.CurrentThread.ManagedThreadId),false);

            var ctsRegistration2 = cts.Token.Register(() => Console.WriteLine("Canceled 2,ThreadId "+Thread.CurrentThread.ManagedThreadId));
            //销毁回调方法。就不会执行了。
            ctsRegistration2.Dispose();
            ThreadPool.QueueUserWorkItem(o => Count(cts.Token, 1000));
            //如果选择Flase,那么会把所有方法执行完后再抛出异常
            cts.Cancel(true);

            var cts1 = new CancellationTokenSource();
            cts1.Token.Register(() => Console.WriteLine("cts1 canceled"));

            var cts2 = new CancellationTokenSource();
            cts2.Token.Register(() => Console.WriteLine("cts2 canceled"));

            //他在cts1或cts2取消时取消
            var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cts1.Token, cts2.Token);
            linkedCts.Token.Register(() => Console.WriteLine("linkedCts canceled"));
            cts2.Cancel();
            Console.WriteLine("cts1={0},cts2={1},linkedCts={2}",
                cts1.IsCancellationRequested, cts2.IsCancellationRequested, linkedCts.IsCancellationRequested); 
        }

 任务完成时自动启动新任务：

        private static void TaskDemo()
        {
            var task = new Task<int>(n => Sum((int)n), 100);
            task.Start();
            Thread.Sleep(4000);
            task.Wait();
            Console.WriteLine("The Sum is :" + task.Result);

            CancellationTokenSource cts = new CancellationTokenSource();
            Task<int> CancelT = Task.Run(() => Sum(cts.Token, 100), cts.Token);
            cts.Cancel();//任务还没开始，则任务无法再调度了，如果已经开始了，只能显示停止任务。所以需要修改sum方法传入一个Toke,
            try
            {
                Console.WriteLine("The sum is:" + CancelT.Result);
            }
            catch(Exception ex)
            {
                Console.WriteLine("CancelT任务终结了，并抛出异常："+ex.ToString());
            }
            Task<int> t = Task.Run(() => Sum(10000));
            t.ContinueWith(ta => Console.WriteLine("The sum is" + ta.Result),
                TaskContinuationOptions.OnlyOnRanToCompletion);
            t.ContinueWith(ta => Console.WriteLine("Sum threw:"+ta.Exception.InnerException),
                TaskContinuationOptions.OnlyOnFaulted);
            t.ContinueWith(ta => Console.WriteLine("Sum was canceled"),
                TaskContinuationOptions.OnlyOnCanceled);
        }

        private static int Sum(int n)
        {
            int sum = 0;
            for(;n>0;n--)
            {
                checked { sum += n; }
            }
            return sum;
        }
        private static int Sum(CancellationToken ct,int n)
        {
            int sum = 0;
            for (; n > 0; n--)
            {
                ct.ThrowIfCancellationRequested();
                checked { sum += n; }
            }
            return sum;
        }

 任务可以启动子任务，任务可以具有父子关系

        /// <summary>
        /// 任务启动子任务
        /// </summary>
        public static void ParentTask()
        {
            Task<int[]> parent = new Task<int[]>(() =>
              {
                  var results = new int[3];
                  new Task(() => results[0] = Sum(10000), TaskCreationOptions.AttachedToParent).Start();//子任务结束，父任务才算结束
                  new Task(() => results[1] = Sum(20000), TaskCreationOptions.AttachedToParent).Start();
                  new Task(() => results[2] = Sum(30000), TaskCreationOptions.AttachedToParent).Start();
                  return results;
              });
            var cwt = parent.ContinueWith(
                ParentTask => Array.ForEach(ParentTask.Result, Console.WriteLine));
            parent.Start();
        }

任务工厂使用

/// <summary>
        /// 任务工厂使用
        /// </summary>
        public static void Parent()
        {
            Task parent = new Task(() =>
            {
                //任务工厂可以统一进行配置，TaskFactory创建的所有Task对象都使用默认的
                //TaskScheduler
                var cts = new CancellationTokenSource();
                var tf = new TaskFactory<int>(cts.Token, TaskCreationOptions.AttachedToParent,
                    TaskContinuationOptions.ExecuteSynchronously,
                    TaskScheduler.Default);
                
                var childTasks = new[]
                {
                tf.StartNew(()=>Sum(cts.Token,1000)),
                tf.StartNew(()=>Sum(cts.Token,2000)),
                tf.StartNew(()=>Sum(cts.Token,3000))
                };
                //为每个字任务添加延续任务，只要一个任务出现异常，终止其他任务
                for (int task = 0; task < childTasks.Length; task++)
                {
                    childTasks[task].ContinueWith(
                        t => cts.Cancel(), TaskContinuationOptions.OnlyOnFaulted);
                }
                //当所有任务结束，取所有子任务（不包括异常和取消）结果最大值，最后延续子任务输出该值。
                tf.ContinueWhenAll(
                    childTasks,
                    completedTasks => completedTasks.Where(
                        t => !t.IsFaulted && !t.IsCanceled).Max(t => t.Result),
                    CancellationToken.None)//CancellationToken.None表示该任务不能被取消
                    .ContinueWith(t => Console.WriteLine("The maximum is:" + t.Result),
                    TaskContinuationOptions.ExecuteSynchronously);
            });
            parent.Start();
        }