生产消费者队列（TaskCompletionSource）的应用

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApplication6
{
    public class PCQueue : IDisposable
    {
        class WorkItem
        {
            public readonly TaskCompletionSource<object> TaskSource;
            public readonly Action Action;
            public readonly CancellationToken? CancelToken;

            public WorkItem(
              TaskCompletionSource<object> taskSource,
              Action action,
              CancellationToken? cancelToken)
            {
                
                TaskSource = taskSource;
                Action = action;
                CancelToken = cancelToken;
            }
        }

        BlockingCollection<WorkItem> _taskQ = new BlockingCollection<WorkItem>();

        /// <summary>
        /// 为每个消费者创建并启动单独的任务： 这里我启动了2个任务，用于打印easy和easy2这两个的顺序不一定
        /// </summary>
        /// <param name="workerCount"></param>
        public PCQueue(int workerCount)
        {
            // 为每个消费者创建并启动单独的任务：
            for (int i = 0; i < workerCount; i++)
                Task.Factory.StartNew(Consume);
        }

        public void Dispose() { _taskQ.CompleteAdding(); }

        /// <summary>
        /// 默认任务取消标识为null的任务进队方法
        /// </summary>
        /// <param name="action"></param>
        /// <returns></returns>
        public Task EnqueueTask(Action action)
        {
            return EnqueueTask(action, null);
        }
        /// <summary>
        /// 任务进队方法含标识
        /// </summary>
        /// <param name="action"></param>
        /// <param name="cancelToken"></param>
        /// <returns></returns>
        public Task EnqueueTask(Action action, CancellationToken? cancelToken)
        {
            var tcs = new TaskCompletionSource<object>();
            _taskQ.Add(new WorkItem(tcs, action, cancelToken));
            //通过TaskCompletionSource返回任务本身，可查看任务的响应信息如result，exception,status等等
            return tcs.Task;
        }

        void Consume()
        {
            foreach (WorkItem workItem in _taskQ.GetConsumingEnumerable())
                if (workItem.CancelToken.HasValue &&
                    workItem.CancelToken.Value.IsCancellationRequested)
                {
                    workItem.TaskSource.SetCanceled();
                }
                else
                    try
                    {
                        workItem.Action();
                        workItem.TaskSource.SetResult(1234);   // 表示完成
                    }
                    catch (OperationCanceledException ex)
                    {
                        if (ex.CancellationToken == workItem.CancelToken)
                            workItem.TaskSource.SetCanceled();
                        else
                            workItem.TaskSource.SetException(ex);
                    }
                    catch (Exception ex)
                    {
                        workItem.TaskSource.SetException(ex);
                    }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            CancellationToken token1 = new CancellationToken(true);
            //
            var pcQ = new PCQueue(2);
            Task task = pcQ.EnqueueTask(() => Console.WriteLine("Easy!"),token1);//输出easy的任务不会执行
            task = pcQ.EnqueueTask(() => Console.WriteLine("Easy2!"));//会执行
         
            // ...
            Console.Read();
        }
    }
}