NullableIntMinMaxAggregationOperator.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Inlined / NullableIntMinMaxAggregationOperator.cs / 1305376 / NullableIntMinMaxAggregationOperator.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// NullableIntMinMaxAggregationOperator.cs 
//
// [....] 
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// An inlined min/max aggregation and its enumerator, for Nullable ints.
    /// 
    internal sealed class NullableIntMinMaxAggregationOperator : InlinedAggregationOperator 
    {
        private readonly int m_sign; // The sign (-1 for min, 1 for max). 
 
        //----------------------------------------------------------------------------------------
        // Constructs a new instance of a min/max associative operator. 
        //

        internal NullableIntMinMaxAggregationOperator(IEnumerable child, int sign) : base(child)
        { 
            Contract.Assert(sign == -1 || sign == 1, "invalid sign");
            m_sign = sign; 
        } 

        //--------------------------------------------------------------------------------------- 
        // 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 int? 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))
            { 
                // Just return null right away for empty results. 
                if (!enumerator.MoveNext())
                { 
                    return null;
                }

                int? best = enumerator.Current; 

                // Based on the sign, do either a min or max reduction. 
                if (m_sign == -1) 
                {
                    while (enumerator.MoveNext()) 
                    {
                        int? current = enumerator.Current;
                        if (best == null || current < best)
                        { 
                            best = current;
                        } 
                    } 
                }
                else 
                {
                    while (enumerator.MoveNext())
                    {
                        int? current = enumerator.Current; 
                        if (best == null || current > best)
                        { 
                            best = current; 
                        }
                    } 
                }

                return best;
            } 
        }
 
        //--------------------------------------------------------------------------------------- 
        // Creates an enumerator that is used internally for the final aggregation step.
        // 

        protected override QueryOperatorEnumerator CreateEnumerator(
            int index, int count, QueryOperatorEnumerator source, object sharedData, CancellationToken cancellationToken)
        { 
            return new NullableIntMinMaxAggregationOperatorEnumerator(source, index, m_sign, cancellationToken);
        } 
 
        //---------------------------------------------------------------------------------------
        // This enumerator type encapsulates the intermediary aggregation over the underlying 
        // (possibly partitioned) data source.
        //

        private class NullableIntMinMaxAggregationOperatorEnumerator : InlinedAggregationOperatorEnumerator 
        {
            private QueryOperatorEnumerator m_source; // The source data. 
            private int m_sign; // The sign for comparisons (-1 means min, 1 means max). 

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

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

            //--------------------------------------------------------------------------------------- 
            // Tallies up the min/max of the underlying data source, walking the entire thing the first
            // time MoveNext is called on this object. 
            // 

            protected override bool MoveNextCore(ref int? currentElement) 
            {
                // Based on the sign, do either a min or max reduction.
                QueryOperatorEnumerator source = m_source;
                TKey keyUnused = default(TKey); 

                if (source.MoveNext(ref currentElement, ref keyUnused)) 
                { 
                    int i = 0;
                    // We just scroll through the enumerator and find the min or max. 
                    if (m_sign == -1)
                    {
                        int? elem = default(int?);
                        while (source.MoveNext(ref elem, ref keyUnused)) 
                        {
                            if ((i++ & CancellationState.POLL_INTERVAL) == 0) 
                                CancellationState.ThrowIfCanceled(m_cancellationToken); 

                            if (currentElement == null || elem < currentElement) 
                            {
                                currentElement = elem;
                            }
                        } 
                    }
                    else 
                    { 
                        int? elem = default(int?);
                        while (source.MoveNext(ref elem, ref keyUnused)) 
                        {
                            if ((i++ & CancellationState.POLL_INTERVAL) == 0)
                                CancellationState.ThrowIfCanceled(m_cancellationToken);
                            if (currentElement == null || elem > currentElement) 
                            {
                                currentElement = elem; 
                            } 
                        }
                    } 

                    // The sum has been calculated. Now just return.
                    return true;
                } 

                return false; 
            } 

            //---------------------------------------------------------------------------------------- 
            // 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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NullableIntMinMaxAggregationOperator.cs source code in C# .NET

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