UA-.NETStandard/Libraries/Opc.Ua.Server/Subscription/MonitoredItem/Queue/EventMonitoredItemQueue.cs

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 *
 * OPC Foundation MIT License 1.00
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using System;
using System.Collections.Generic;
using Microsoft.Extensions.Logging;

namespace Opc.Ua.Server
{
    /// <summary>
    /// Provides a queue for events.
    /// </summary>
    public class EventMonitoredItemQueue : IEventMonitoredItemQueue
    {
        private const uint kMaxNoOfEntriesCheckedForDuplicateEvents = 1000;

        /// <summary>
        /// Creates an empty queue.
        /// </summary>
        public EventMonitoredItemQueue(bool createDurable, uint monitoredItemId, ITelemetryContext telemetry)
        {
            m_logger = telemetry.CreateLogger<DataChangeMonitoredItemQueue>();
            if (createDurable)
            {
                m_logger.LogError(
                    "EventMonitoredItemQueue does not support durable queues, please provide full implementation of IDurableMonitoredItemQueue using Server.CreateDurableMonitoredItemQueueFactory to supply own factory");
                throw new ArgumentException(
                    "DataChangeMonitoredItemQueue does not support durable Queues",
                    nameof(createDurable));
            }
            m_events = [];
            MonitoredItemId = monitoredItemId;
            QueueSize = 0;
        }

        /// <inheritdoc/>
        public uint MonitoredItemId { get; }

        /// <inheritdoc/>
        public virtual bool IsDurable => false;

        /// <inheritdoc/>
        public uint QueueSize { get; protected set; }

        /// <inheritdoc/>
        public int ItemsInQueue => m_events.Count;

        /// <inheritdoc/>
        public bool Dequeue(out EventFieldList value)
        {
            value = null!;
            if (m_events.Count != 0)
            {
                value = m_events[0];
                m_events.RemoveAt(0);
                return true;
            }
            return false;
        }

        /// <inheritdoc/>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// An overrideable version of the Dispose.
        /// </summary>
        protected virtual void Dispose(bool disposing)
        {
        }

        /// <inheritdoc/>
        public void Enqueue(EventFieldList value)
        {
            if (QueueSize == 0)
            {
                throw new ServiceResultException(
                    StatusCodes.BadInternalError,
                    "Error queueing Event. Queue size is set to 0");
            }

            //Discard oldest
            if (m_events.Count == QueueSize)
            {
                Dequeue(out EventFieldList _);
            }

            m_events.Add(value);
        }

        /// <inheritdoc/>
        public bool IsEventContainedInQueue(IFilterTarget instance)
        {
            int maxCount =
                m_events.Count > kMaxNoOfEntriesCheckedForDuplicateEvents
                    ? (int)kMaxNoOfEntriesCheckedForDuplicateEvents
                    : m_events.Count;

            for (int i = 0; i < maxCount; i++)
            {
                if (m_events[i] is EventFieldList processedEvent &&
                    ReferenceEquals(instance, processedEvent.Handle))
                {
                    return true;
                }
            }
            return false;
        }

        /// <inheritdoc/>
        public void SetQueueSize(uint queueSize, bool discardOldest)
        {
            QueueSize = queueSize;

            if (m_events.Count > QueueSize)
            {
                if (discardOldest)
                {
                    m_events.RemoveRange(0, m_events.Count - (int)queueSize);
                }
                else
                {
                    m_events.RemoveRange((int)queueSize, m_events.Count - (int)queueSize);
                }
            }
        }

        /// <summary>
        /// the contained in the queue
        /// </summary>
        protected List<EventFieldList> m_events;

        /// <summary>
        /// The logger to use here and in derived classes
        /// </summary>
        protected ILogger m_logger;
    }
}