gistfile1.txt

public class ConcurrentLeastFrequentlyUse<T> where T : class
{
	private readonly int[] generationSizes;
	private readonly ConcurrentQueue<T>[] queues;

	public ConcurrentLeastFrequentlyUse(params int[] generationSizes)
	{
		this.generationSizes = generationSizes;
		queues =new ConcurrentQueue<T>[generationSizes.Length];
	}

	public event Action<T> ItemDropped;

	internal void InvokeItemDropped(T item)
	{
		var handler = ItemDropped;
		if (handler != null) 
			handler(item);
	}

	public void Use(T item)
	{
		queues[0].Enqueue(item);

		T lastItem = null;
		for (int i = 0; i < generationSizes.Length; i++)
		{
			if (queues[i].Count <= generationSizes[i]) 
				continue;
			if (!queues[i].TryDequeue(out lastItem)) 
				continue;
			if ((i + 1) >= generationSizes.Length)
				break;
			queues[i + 1].Enqueue(lastItem);
			lastItem = default(T);
		}

		if(lastItem != default(T))
			InvokeItemDropped(lastItem);

	}
}