UA-.NETStandard/SampleApplications/Samples/Opc.Ua.Sample/Base/MonitoredItemQueue.cs

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 *
 * OPC Foundation MIT License 1.00
 * 
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 * obtaining a copy of this software and associated documentation
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using System;
using System.Collections.Generic;
using System.Text;

namespace Opc.Ua.Sample
{
    /// <summary>
    /// Provides a queue for data changes.
    /// </summary>
    public class MonitoredItemQueue
    {
        /// <summary>
        /// Creates an empty queue.
        /// </summary>
        public MonitoredItemQueue()
        {
            m_values = null;
            m_errors = null;
            m_start = -1;
            m_end = -1;
            m_overflow = -1;
            m_discardOldest = false;
            m_nextSampleTime = 0;
            m_samplingInterval = 0;
        }
        
        #region Public Methods
        /// <summary>
        /// Gets the current queue size.
        /// </summary>
        public uint QueueSize
        {
            get 
            {
                if (m_values == null)
                {
                    return 0;
                }

                return (uint)m_values.Length; 
            }
        }
        
        /// <summary>
        /// Sets the sampling interval used when queuing values.
        /// </summary>
        /// <param name="samplingInterval">The new sampling interval.</param>
        public void SetSamplingInterval(double samplingInterval)
        {
            // substract the previous sampling interval.
            if (m_samplingInterval < m_nextSampleTime)
            {
                m_nextSampleTime -= m_samplingInterval;
            }

            // calculate the next sampling interval.
            m_samplingInterval = (long)(samplingInterval*TimeSpan.TicksPerMillisecond);

            if (m_samplingInterval > 0)
            {
                m_nextSampleTime += m_samplingInterval;
            }
            else
            {
                m_nextSampleTime = 0;
            }
        }

        /// <summary>
        /// Sets the queue size.
        /// </summary>
        /// <param name="queueSize">The new queue size.</param>
        /// <param name="discardOldest">Whether to discard the oldest values if the queue overflows.</param>
        /// <param name="diagnosticsMasks">Specifies which diagnostics which should be kept in the queue.</param>
        public void SetQueueSize(uint queueSize, bool discardOldest, DiagnosticsMasks diagnosticsMasks)
        {
            int length = (int)queueSize;

            if (length < 1)
            {
                length = 1;
            }

            int start = m_start;
            int end = m_end;

            // create new queue.
            DataValue[] values = new DataValue[length];            
            ServiceResult[] errors = null;

            if ((diagnosticsMasks & DiagnosticsMasks.OperationAll) != 0)
            {
                errors = new ServiceResult[length];
            }
            
            // copy existing values.
            List<DataValue> existingValues = null;
            List<ServiceResult> existingErrors = null;

            if (m_start >= 0)
            {
                existingValues = new List<DataValue>();
                existingErrors = new List<ServiceResult>();

                DataValue value = null;
                ServiceResult error = null;

                while (Dequeue(out value, out error))
                {
                    existingValues.Add(value);
                    existingErrors.Add(error);
                }
            }

            // update internals.
            m_values = values;
            m_errors = errors;
            m_start = -1;
            m_end = 0;
            m_overflow = -1;
            m_discardOldest = discardOldest;

            // requeue the data.
            if (existingValues != null)
            {
                for (int ii = 0; ii < existingValues.Count; ii++)
                {
                    Enqueue(existingValues[ii], existingErrors[ii]);
                }
            }
        }
        
        /// <summary>
        /// Adds the value to the queue.
        /// </summary>
        /// <param name="value">The value to queue.</param>
        /// <param name="error">The error to queue.</param>
        public void QueueValue(DataValue value, ServiceResult error)
        {
            long now = DateTime.UtcNow.Ticks;

            if (m_start >= 0)
            {
                // check if too soon for another sample.
                if (now < m_nextSampleTime)
                {
                    int last = m_end-1;

                    if (last < 0)
                    {
                        last = m_values.Length-1;
                    }

                    // replace last value and error.
                    m_values[last] = value;

                    if (m_errors != null)
                    {
                        m_errors[last] = error;
                    }

                    return;
                }
            }

            // update next sample time.
            if (m_nextSampleTime > 0)
            {
                long delta = now - m_nextSampleTime;

                if (m_samplingInterval > 0 && delta >= 0)
                {
                    m_nextSampleTime += ((delta/m_samplingInterval)+1)*m_samplingInterval;                 
                }
            }
            else
            {
                m_nextSampleTime = now + m_samplingInterval;
            }

            // queue next value.
            Enqueue(value, error);
        }

        /// <summary>
        /// Publishes the oldest value in the queue.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <param name="error">The error associated with the value.</param>
        /// <returns>True if a value was found. False if the queue is empty.</returns>
        public bool Publish(out DataValue value, out ServiceResult error)
        {
            return Dequeue(out value, out error);
        }
        #endregion
        
        #region Private Methods
        /// <summary>
        /// Adds the value to the queue. Discards values if the queue is full.
        /// </summary>
        /// <param name="value">The value to add.</param>
        /// <param name="error">The error to add.</param>
        private void Enqueue(DataValue value, ServiceResult error)
        {
            // check for empty queue.
            if (m_start < 0)
            {
                m_start = 0;
                m_end = 1;
                m_overflow = -1;

                m_values[m_start] = value;

                if (m_errors != null)
                {
                    m_errors[m_start] = error;
                }

                return;
            }

            int next = m_end;

            // check for wrap around.
            if (next >= m_values.Length)
            {
                next = 0;
            }

            // check if queue is full.
            if (m_start == next)
            {
                if (!m_discardOldest)
                {
                    m_overflow = m_end-1;
                    return;
                }

                // remove oldest value.
                m_start++;

                if (m_start >= m_values.Length)
                {
                    m_start = 0;
                }

                // set overflow bit.
                m_overflow = m_start;
            }

            // add value.
            m_values[next] = value;

            if (m_errors != null)
            {
                m_errors[next] = error;
            }

            m_end = next+1;
        }

        /// <summary>
        /// Removes a value and an error from the queue.
        /// </summary>
        /// <param name="value">The value removed from the queue.</param>
        /// <param name="error">The error removed from the queue.</param>
        /// <returns>True if a value was found. False if the queue is empty.</returns>
        private bool Dequeue(out DataValue value, out ServiceResult error)
        {
            value = null;
            error = null;

            // check for empty queue.
            if (m_start < 0)
            {
                return false;
            }

            value = m_values[m_start];
            m_values[m_start] = null;
            
            if (m_errors != null)
            {
                error = m_errors[m_start];
                m_errors[m_start] = null;
            }

            // set the overflow bit.
            if (m_overflow == m_start)
            {
                SetOverflowBit(ref value, ref error);
                m_overflow = -1;
            }

            m_start++;
            
            // check if queue has been emptied.
            if (m_start == m_end)
            {
                m_start = -1;
                m_end = 0;
            }

            // check for wrap around.
            else if (m_start >= m_values.Length)
            {
                m_start = 0;
            }
            
            return true;
        }

        /// <summary>
        /// Sets the overflow bit in the value and error.
        /// </summary>
        /// <param name="value">The value to update.</param>
        /// <param name="error">The error to update.</param>
        private void SetOverflowBit(ref DataValue value, ref ServiceResult error)
        {
            if (value != null)
            {
                StatusCode status = value.StatusCode;
                status.Overflow = true;
                value.StatusCode = status;
            }

            if (error != null)
            {
                StatusCode status = error.StatusCode;
                status.Overflow = true;

                // have to copy before updating because the ServiceResult is invariant.
                ServiceResult copy = new ServiceResult(
                    status,
                    error.SymbolicId,
                    error.NamespaceUri,
                    error.LocalizedText,
                    error.AdditionalInfo,
                    error.InnerResult);

                error = copy;
            }
        }
        #endregion

        #region Private Fields
        private DataValue[] m_values;
        private ServiceResult[] m_errors;
        private int m_start;
        private int m_end;
        private int m_overflow;
        private bool m_discardOldest;
        private long m_nextSampleTime;
        private long m_samplingInterval;
        #endregion
    }
}