Synnefo » Pithos MS Client

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

// <copyright file="AsyncSemaphore.cs" company="Microsoft">

// TODO: Update copyright text.

// </copyright>

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

using System.Threading.Tasks;

namespace Pithos.Core

{

    using System;

    using System.Collections.Generic;

    using System.Linq;

    using System.Text;

    /// <summary>

    /// TODO: Update summary.

    /// </summary>

    public class AsyncSemaphore

    {

        private readonly static Task s_completed = TaskEx.FromResult(true);

        private readonly Queue<TaskCompletionSource<bool>> m_waiters = new Queue<TaskCompletionSource<bool>>();

        private int m_currentCount; 

        public AsyncSemaphore(int initialCount)

        {

            if (initialCount < 0) throw new ArgumentOutOfRangeException("initialCount");

            m_currentCount = initialCount; 

        }

        public Task WaitAsync()

        {

            lock (m_waiters)

            {

                if (m_currentCount > 0)

                {

                    --m_currentCount;

                    return s_completed;

                }

                else

                {

                    var waiter = new TaskCompletionSource<bool>();

                    m_waiters.Enqueue(waiter);

                    return waiter.Task;

                }

            }

        }

        public void Release()

        {

            TaskCompletionSource<bool> toRelease = null;

            lock (m_waiters)

            {

                if (m_waiters.Count > 0)

                    toRelease = m_waiters.Dequeue();

                else

                    ++m_currentCount;

            }

            if (toRelease != null)

                toRelease.SetResult(true);

        }

    }

}