OpenSim-Test/OpenSim/Region/ClientStack/Linden/UDP/IncomingPacketHistoryCollection.cs

/*
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 *       documentation and/or other materials provided with the distribution.
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 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 */

using System;
using System.Collections.Generic;

namespace OpenSim.Region.ClientStack.LindenUDP
{
    /// <summary>
    /// A circular buffer and hashset for tracking incoming packet sequence
    /// numbers
    /// </summary>
    public sealed class IncomingPacketHistoryCollection
    {
        private readonly uint[] m_items;
        private HashSet<uint> m_hashSet;
        private int m_first;
        private int m_next;
        private int m_capacity;

        public IncomingPacketHistoryCollection(int capacity)
        {
            this.m_capacity = capacity;
            m_items = new uint[capacity];
            m_hashSet = new HashSet<uint>();
        }

        public bool TryEnqueue(uint ack)
        {
            lock (m_hashSet)
            {
                if (m_hashSet.Add(ack))
                {
                    m_items[m_next] = ack;
                    m_next = (m_next + 1) % m_capacity;
                    if (m_next == m_first)
                    {
                        m_hashSet.Remove(m_items[m_first]);
                        m_first = (m_first + 1) % m_capacity;
                    }

                    return true;
                }
            }

            return false;
        }
    }
}