向集合添加优先级限制和阻塞功能

自定义集合类是一个基本优先级别队列，优先级别在其中表示为 System.Collections.Concurrent.ConcurrentQueue<T> 对象的数组。在每个队列中不进行其他排序。通过实现类中的 System.Collections.Concurrent.IProducerConsumerCollection<T> 接口，然后将类实例用作 System.Collections.Concurrent.BlockingCollection<T> 的内部存储机制，来向自定义集合类添加限制和阻塞功能。

namespace ProdConsumerCS
{
    using System;
    using System.Collections;
    using System.Collections.Concurrent;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.Linq;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;

    // 实现具有边界和阻止功能的优先级队列。
    public class SimplePriorityQueue<TPriority, TValue> : IProducerConsumerCollection<KeyValuePair<int, TValue>>
    {
        // 数组中每一个队列表示同一个优先级. 
        // 队列中的元素具有相同的优先级
        private ConcurrentQueue<KeyValuePair<int, TValue>>[] _queues = null;

        // 内部存储的队列个数.
        private int priorityCount = 0;
        private int m_count = 0;

        public SimplePriorityQueue(int priCount)
        {
            this.priorityCount = priCount;
            _queues = new ConcurrentQueue<KeyValuePair<int, TValue>>[priorityCount];
            for (int i = 0; i < priorityCount; i++)
                _queues[i] = new ConcurrentQueue<KeyValuePair<int, TValue>>();
        }

        // IProducerConsumerCollection members
        public bool TryAdd(KeyValuePair<int, TValue> item)
        {
            _queues[item.Key].Enqueue(item);
            Interlocked.Increment(ref m_count);
            return true;
        }

        public bool TryTake(out KeyValuePair<int, TValue> item)
        {
            bool success = false;

            // Loop through the queues in priority order
            // looking for an item to dequeue.
            for (int i = 0; i < priorityCount; i++)
            {
                // Lock the internal data so that the Dequeue
                // operation and the updating of m_count are atomic.
                lock (_queues)
                {
                    success = _queues[i].TryDequeue(out item);
                    if (success)
                    {
                        Interlocked.Decrement(ref m_count);
                        return true;
                    }
                }
            }

            // If we get here, we found nothing. 
            // Assign the out parameter to its default value and return false.
            item = new KeyValuePair<int, TValue>(0, default(TValue));
            return false;
        }

        public int Count
        {
            get { return m_count; }
        }

        // Required for ICollection
        void ICollection.CopyTo(Array array, int index)
        {
            CopyTo(array as KeyValuePair<int, TValue>[], index);
        }

        // CopyTo is problematic in a producer-consumer.
        // The destination array might be shorter or longer than what 
        // we get from ToArray due to adds or takes after the destination array was allocated.
        // Therefore, all we try to do here is fill up destination with as much
        // data as we have without running off the end.                
        public void CopyTo(KeyValuePair<int, TValue>[] destination, int destStartingIndex)
        {
            if (destination == null) throw new ArgumentNullException();
            if (destStartingIndex < 0) throw new ArgumentOutOfRangeException();

            int remaining = destination.Length;
            KeyValuePair<int, TValue>[] temp = this.ToArray();
            for (int i = 0; i < destination.Length && i < temp.Length; i++)
                destination[i] = temp[i];
        }

        public KeyValuePair<int, TValue>[] ToArray()
        {
            KeyValuePair<int, TValue>[] result;

            lock (_queues)
            {
                result = new KeyValuePair<int, TValue>[this.Count];
                int index = 0;
                foreach (var q in _queues)
                {
                    if (q.Count > 0)
                    {
                        q.CopyTo(result, index);
                        index += q.Count;
                    }
                }
                return result;
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        public IEnumerator<KeyValuePair<int, TValue>> GetEnumerator()
        {
            for (int i = 0; i < priorityCount; i++)
            {
                foreach (var item in _queues[i])
                    yield return item;
            }
        }

        public bool IsSynchronized
        {
            get
            {
                throw new NotSupportedException();
            }
        }

        public object SyncRoot
        {
            get { throw new NotSupportedException(); }
        }
    }

    public class TestBlockingCollection
    {
        static void Main()
        {

            int priorityCount = 7;
            SimplePriorityQueue<int, int> queue = new SimplePriorityQueue<int, int>(priorityCount);
            var bc = new BlockingCollection<KeyValuePair<int, int>>(queue, 50);


            CancellationTokenSource cts = new CancellationTokenSource();

            Task.Run(() =>
                {
                    if (Console.ReadKey(true).KeyChar == 'c')
                        cts.Cancel();
                });

            // Create a Task array so that we can Wait on it
            // and catch any exceptions, including user cancellation.
            Task[] tasks = new Task[2];

            // Create a producer thread. You can change the code to 
            // make the wait time a bit slower than the consumer 
            // thread to demonstrate the blocking capability.
            tasks[0] = Task.Run(() =>
            {
                // We randomize the wait time, and use that value
                // to determine the priority level (Key) of the item.
                Random r = new Random();

                int itemsToAdd = 40;
                int count = 0;
                while (!cts.Token.IsCancellationRequested && itemsToAdd-- > 0)
                {
                    int waitTime = r.Next(2000);
                    int priority = waitTime % priorityCount;
                    var item = new KeyValuePair<int, int>(priority, count++);

                    bc.Add(item);
                    Console.WriteLine("added pri {0}, data={1}", item.Key, item.Value);
                }
                Console.WriteLine("Producer is done adding.");
                bc.CompleteAdding();
            },
             cts.Token);

            //Give the producer a chance to add some items.
            Thread.SpinWait(1000000);

            // Create a consumer thread. The wait time is
            // a bit slower than the producer thread to demonstrate
            // the bounding capability at the high end. Change this value to see
            // the consumer run faster to demonstrate the blocking functionality
            // at the low end.

            tasks[1] = Task.Run(() =>
                {
                    while (!bc.IsCompleted && !cts.Token.IsCancellationRequested)
                    {
                        Random r = new Random();
                        int waitTime = r.Next(2000);
                        Thread.SpinWait(waitTime * 70);

                        // KeyValuePair is a value type. Initialize to avoid compile error in if(success)
                        KeyValuePair<int, int> item = new KeyValuePair<int, int>();
                        bool success = false;
                        success = bc.TryTake(out item);
                        if (success)
                        {
                            // Do something useful with the data.
                            Console.WriteLine("removed Pri = {0} data = {1} collCount= {2}", item.Key, item.Value, bc.Count);
                        }
                        else
                            Console.WriteLine("No items to retrieve. count = {0}", bc.Count);
                    }
                    Console.WriteLine("Exited consumer loop");
                },
                cts.Token);

            try {
                Task.WaitAll(tasks, cts.Token);
            }
            catch (OperationCanceledException e) {
                if (e.CancellationToken == cts.Token)
                    Console.WriteLine("Operation was canceled by user. Press any key to exit");
            }
            catch (AggregateException ae) {
                foreach (var v in ae.InnerExceptions)
                    Console.WriteLine(v.Message);
            }
            finally {
                cts.Dispose();
            }

            Console.ReadKey(true);

        }
    }

}

 默认情况下，System.Collections.Concurrent.BlockingCollection<T> 的存储为 System.Collections.Concurrent.ConcurrentQueue<T>。