using System;

using System.Collections.Generic;

using System.Collections.Concurrent;

using System.Threading;                 

using System.Threading.Tasks;

​

namespace Example

{

    public class FifoMonitor

    {

        public class FifoCriticalSection : IDisposable

        {

            private readonly FifoMonitor _parent;

            public FifoCriticalSection(FifoMonitor parent)

            {

                _parent = parent;

                _parent.Enter();

            }

            public void Dispose()

            {

                _parent.Exit();

            }

        }

        private object _innerLock = new object();

        private volatile int counter = 0;

        private volatile int current = 1;

        public FifoCriticalSection Lock()

        {

            return new FifoCriticalSection(this);

        }

        private void Enter()

        {

            int mine = Interlocked.Increment(ref counter);

            Monitor.Enter(_innerLock);

            while (current != mine) Monitor.Wait(_innerLock);

        }

        private void Exit()

        {

            Interlocked.Increment(ref current);

            Monitor.PulseAll(_innerLock);

            Monitor.Exit(_innerLock);

        }

    }

​

    public class QueuedBlockingCollection<T> : BlockingCollection<T>

    {

        private FifoMonitor monitor = new FifoMonitor();

        public QueuedBlockingCollection(int max) : base (max) {}

        public void Enqueue(T item)

        {

            using (monitor.Lock())

            {

                base.Add(item);

            }

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            //Setup

            var blockingCollection = new QueuedBlockingCollection<int>(10);

            var tasks = new Task[10];

            //Block the collection by filling it up

            for (int i=1; i<=10; i++) blockingCollection.Add(99);

            //Start 10 threads all trying to add another value

            for (int i=1; i<=10; i++)

            {

                int index = i; //unclose

                tasks[index-1] = Task.Run( () => blockingCollection.Enqueue(index) );

                Task.Delay(100).Wait();  //Wait long enough for the Enqueue call to block

            }

            //Purge the collection, making room for more values

            while (blockingCollection.Count > 0)

            {

                var n = blockingCollection.Take();

                Console.WriteLine(n);

            }

            //Wait for our pending adds to complete

            Task.WaitAll(tasks);

​

            //Display the collection in the order read

            while (blockingCollection.Count > 0)

            {

                var n = blockingCollection.Take();

                Console.WriteLine(n);

            }

​

        }

    }

}