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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// CountAggregationOperator.cs
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
namespace System.Linq.Parallel
{
/// <summary>
/// An inlined count aggregation and its enumerator.
/// </summary>
/// <typeparam name="TSource"></typeparam>
internal sealed class CountAggregationOperator<TSource> : InlinedAggregationOperator<TSource, int, int>
{
//---------------------------------------------------------------------------------------
// Constructs a new instance of the operator.
//
internal CountAggregationOperator(IEnumerable<TSource> 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<int> 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<int, int> CreateEnumerator<TKey>(
int index, int count, QueryOperatorEnumerator<TSource, TKey> source, object? sharedData,
CancellationToken cancellationToken)
{
return new CountAggregationOperatorEnumerator<TKey>(source, index, cancellationToken);
}
//---------------------------------------------------------------------------------------
// This enumerator type encapsulates the intermediary aggregation over the underlying
// (possibly partitioned) data source.
//
private sealed class CountAggregationOperatorEnumerator<TKey> : InlinedAggregationOperatorEnumerator<int>
{
private readonly QueryOperatorEnumerator<TSource, TKey> _source; // The source data.
//---------------------------------------------------------------------------------------
// Instantiates a new aggregation operator.
//
internal CountAggregationOperatorEnumerator(QueryOperatorEnumerator<TSource, TKey> source, int partitionIndex,
CancellationToken cancellationToken) :
base(partitionIndex, cancellationToken)
{
Debug.Assert(source != null);
_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<TSource, TKey> source = _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)
_cancellationToken.ThrowIfCancellationRequested();
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)
{
Debug.Assert(_source != null);
_source.Dispose();
}
}
}
}
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