Synnefo » Pithos MS Client

//--------------------------------------------------------------------------

// 

//  Copyright (c) Microsoft Corporation.  All rights reserved. 

// 

//  File: AsyncProducerConsumerCollection.cs

//

//--------------------------------------------------------------------------

using System;

using System.Collections.Concurrent;

using System.Diagnostics;

using System.Threading;

using System.Threading.Tasks;

namespace Pithos.Core

{

    /// <summary>Provides an asynchronous producer/consumer collection.</summary>

    [DebuggerDisplay("Count={CurrentCount}")]

    public sealed class AsyncCollection<T> 

    {

        /// <summary>Asynchronous semaphore used to keep track of asynchronous work.</summary>

        private AsyncSemaphore _semaphore = new AsyncSemaphore(0);

        /// <summary>The data stored in the collection.</summary>

        private IProducerConsumerCollection<T> _collection;

        /// <summary>Initializes the asynchronous producer/consumer collection to store data in a first-in-first-out (FIFO) order.</summary>

        public AsyncCollection() : this(new ConcurrentQueue<T>()) { }

        /// <summary>Initializes the asynchronous producer/consumer collection.</summary>

        /// <param name="collection">The underlying collection to use to store data.</param>

        public AsyncCollection(IProducerConsumerCollection<T> collection)

        {

            if (collection == null) throw new ArgumentNullException("collection");

            _collection = collection;

        }

        /// <summary>Adds an element to the collection.</summary>

        /// <param name="item">The item to be added.</param>

        public void Add(T item)

        {

            if (_collection.TryAdd(item))

                Task.Factory.StartNew(s => ((AsyncSemaphore)s).Release(),

                    _semaphore, CancellationToken.None, TaskCreationOptions.PreferFairness, TaskScheduler.Default);

            else throw new InvalidOperationException("Invalid collection");

        }

        /// <summary>Takes an element from the collection asynchronously.</summary>

        /// <returns>A Task that represents the element removed from the collection.</returns>

        public Task<T> Take()

        {

            return _semaphore.WaitAsync().ContinueWith(_ =>

            {

                T result;

                if (!_collection.TryTake(out result)) throw new InvalidOperationException("Invalid collection");

                return result;

            }, TaskContinuationOptions.OnlyOnRanToCompletion);

        }

        /// <summary>Gets the number of elements in the collection.</summary>

        public int Count { get { return _collection.Count; } }

    }

}