﻿ CountAggregationOperator.cs
 File: System\Linq\Parallel\QueryOperators\Inlined\CountAggregationOperator.cs Project: ndp\fx\src\Core\System.Core.csproj (System.Core)
 // ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // CountAggregationOperator.cs // // Microsoft // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections.Generic; using System.Diagnostics.Contracts; using System.Threading; namespace System.Linq.Parallel { /// /// An inlined count aggregation and its enumerator. /// /// internal sealed class CountAggregationOperator : InlinedAggregationOperator { //--------------------------------------------------------------------------------------- // Constructs a new instance of the operator. // internal CountAggregationOperator(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 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)) { // We just reduce the elements in each output partition. int count = 0; while (enumerator.MoveNext()) { checked { count += enumerator.Current; } } return count; } } //--------------------------------------------------------------------------------------- // 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 CountAggregationOperatorEnumerator(source, index, cancellationToken); } //--------------------------------------------------------------------------------------- // This enumerator type encapsulates the intermediary aggregation over the underlying // (possibly partitioned) data source. // private class CountAggregationOperatorEnumerator : InlinedAggregationOperatorEnumerator { private readonly QueryOperatorEnumerator m_source; // The source data. //--------------------------------------------------------------------------------------- // Instantiates a new aggregation operator. // internal CountAggregationOperatorEnumerator(QueryOperatorEnumerator source, int partitionIndex, CancellationToken cancellationToken) : base(partitionIndex, cancellationToken) { Contract.Assert(source != null); m_source = source; } //--------------------------------------------------------------------------------------- // Counts the elements in the underlying data source, walking the entire thing the first // time MoveNext is called on this object. // protected override bool MoveNextCore(ref int currentElement) { TSource elementUnused = default(TSource); TKey keyUnused = default(TKey); QueryOperatorEnumerator source = m_source; if (source.MoveNext(ref elementUnused, ref keyUnused)) { // We just scroll through the enumerator and keep a running count. int count = 0; int i = 0; do { if ((i++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); checked { count++; } } while (source.MoveNext(ref elementUnused, ref keyUnused)); currentElement = count; 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(); } } } }