Acapla

public class AwaitableQueue<T>
{
    private readonly ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();
    private long _count = 0;
    private readonly ConcurrentQueue<TaskCompletionSource<T>> _pending = new ConcurrentQueue<TaskCompletionSource<T>>();

    /// <summary>
    /// Enqueue the specified item. Blocking operation.
    /// </summary>
    /// <param name="item">Item.</param>