NullableIntAverageAggregationOperator.cs source code in C# .NET

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Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Inlined / NullableIntAverageAggregationOperator.cs / 1305376 / NullableIntAverageAggregationOperator.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// NullableIntAverageAggregationOperator.cs 
//
// [....] 
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// An inlined average aggregation operator and its enumerator, for Nullable ints.
    /// 
    internal sealed class NullableIntAverageAggregationOperator : InlinedAggregationOperator, double?> 
    {
        //---------------------------------------------------------------------------------------- 
        // Constructs a new instance of an average associative operator. 
        //
 
        internal NullableIntAverageAggregationOperator(IEnumerable child) : base(child)
        {
        }
 
        //---------------------------------------------------------------------------------------
        // Executes the entire query tree, and aggregates the intermediate results into the 
        // final result based on the binary operators and final reduction. 
        //
        // Return Value: 
        //     The single result of aggregation.
        //

        protected override double? InternalAggregate(ref Exception singularExceptionToThrow) 
        {
            // Because the final reduction is typically much cheaper than the intermediate 
            // reductions over the individual partitions, and because each parallel partition 
            // will do a lot of work to produce a single output element, we prefer to turn off
            // pipelining, and process the final reductions serially. 
            using (IEnumerator> enumerator = GetEnumerator(ParallelMergeOptions.FullyBuffered, true))
            {
                // If the sequence was empty, return null right away.
                if (!enumerator.MoveNext()) 
                {
                    return null; 
                } 

                Pair result = enumerator.Current; 

                // Simply add together the sums and totals.
                while (enumerator.MoveNext())
                { 
                    checked
                    { 
                        result.First += enumerator.Current.First; 
                        result.Second += enumerator.Current.Second;
                    } 
                }

                // And divide the sum by the total to obtain the final result.
                return (double)result.First / result.Second; 
            }
        } 
 
        //---------------------------------------------------------------------------------------
        // Creates an enumerator that is used internally for the final aggregation step. 
        //

        protected override QueryOperatorEnumerator,int> CreateEnumerator(
            int index, int count, QueryOperatorEnumerator source, object sharedData, CancellationToken cancellationToken) 
        {
            return new NullableIntAverageAggregationOperatorEnumerator(source, index, cancellationToken); 
        } 

        //--------------------------------------------------------------------------------------- 
        // This enumerator type encapsulates the intermediary aggregation over the underlying
        // (possibly partitioned) data source.
        //
 
        private class NullableIntAverageAggregationOperatorEnumerator : InlinedAggregationOperatorEnumerator>
        { 
            private QueryOperatorEnumerator m_source; // The source data. 

            //---------------------------------------------------------------------------------------- 
            // Instantiates a new aggregation operator.
            //

            internal NullableIntAverageAggregationOperatorEnumerator(QueryOperatorEnumerator source, int partitionIndex, 
                CancellationToken cancellationToken) :
                base(partitionIndex, cancellationToken) 
            { 
                Contract.Assert(source != null);
                m_source = source; 
            }

            //---------------------------------------------------------------------------------------
            // Tallies up the average of the underlying data source, walking the entire thing the first 
            // time MoveNext is called on this object.
            // 
 
            protected override bool MoveNextCore(ref Pair currentElement)
            { 
                // The temporary result contains the running sum and count, respectively.
                long sum = 0;
                long count = 0;
 
                QueryOperatorEnumerator source = m_source;
                int? current = default(int?); 
                TKey keyUnused = default(TKey); 

                int i = 0; 
                while (source.MoveNext(ref current, ref keyUnused))
                {
                    if ((i++ & CancellationState.POLL_INTERVAL) == 0)
                        CancellationState.ThrowIfCanceled(m_cancellationToken); 

                    if (current.HasValue) 
                    { 
                        sum += current.GetValueOrDefault();
                        count++; 
                    }
                }

                currentElement = new Pair(sum, count); 
                return count > 0;
            } 
 
            //----------------------------------------------------------------------------------------
            // Dispose of resources associated with the underlying enumerator. 
            //

            protected override void Dispose(bool disposing)
            { 
                Contract.Assert(m_source != null);
                m_source.Dispose(); 
            } 
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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