﻿ NullableDoubleMinMaxAggregationOperator.cs
 File: System\Linq\Parallel\QueryOperators\Inlined\NullableDoubleMinMaxAggregationOperator.cs Project: ndp\fx\src\Core\System.Core.csproj (System.Core)
 ```// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // NullableDoubleMinMaxAggregationOperator.cs // // Microsoft // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- 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{Double}s. /// /// Notes: /// Note that normally double.NaN < anything is false, as is anything < NaN. This would /// lead to some strangeness in Min and Max, e.g. Min({ NaN, 5.0 } == NaN, yet /// Min({ 5.0, NaN }) == 5.0! We impose a total ordering so that NaN is smaller than /// everything, including -infinity, which is consistent with Comparer_T. /// internal sealed class NullableDoubleMinMaxAggregationOperator : 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 NullableDoubleMinMaxAggregationOperator(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 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)) { // Just return null right away for empty results. if (!enumerator.MoveNext()) { return null; } double? best = enumerator.Current; // Based on the sign, do either a min or max reduction. if (m_sign == -1) { while (enumerator.MoveNext()) { double? current = enumerator.Current; if (current == null) continue; if (best == null || current < best || double.IsNaN(current.GetValueOrDefault())) { best = current; } } } else { while (enumerator.MoveNext()) { double? current = enumerator.Current; if (current == null) continue; if (best == null || current > best || double.IsNaN(best.GetValueOrDefault())) { 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 NullableDoubleMinMaxAggregationOperatorEnumerator(source, index, m_sign, cancellationToken); } //--------------------------------------------------------------------------------------- // This enumerator type encapsulates the intermediary aggregation over the underlying // (possibly partitioned) data source. // private class NullableDoubleMinMaxAggregationOperatorEnumerator : 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 NullableDoubleMinMaxAggregationOperatorEnumerator(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 double? 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) { double? elem = default(double?); while (source.MoveNext(ref elem, ref keyUnused)) { if ((i++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); if (elem == null) continue; if (currentElement == null || elem < currentElement || double.IsNaN(elem.GetValueOrDefault())) { currentElement = elem; } } } else { double? elem = default(double?); while (source.MoveNext(ref elem, ref keyUnused)) { if ((i++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); if (elem == null) continue; if (currentElement == null || elem > currentElement || double.IsNaN(currentElement.GetValueOrDefault())) { 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(); } } } } ```