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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.
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// IndexedSelectQueryOperator.cs
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
namespace System.Linq.Parallel
{
/// <summary>
/// A variant of the Select operator that supplies element index while performing the
/// projection operation. This requires cooperation with partitioning and merging to
/// guarantee ordering is preserved.
///
/// </summary>
/// <typeparam name="TInput"></typeparam>
/// <typeparam name="TOutput"></typeparam>
internal sealed class IndexedSelectQueryOperator<TInput, TOutput> : UnaryQueryOperator<TInput, TOutput>
{
// Selector function. Used to project elements to a transformed view during execution.
private readonly Func<TInput, int, TOutput> _selector;
private bool _prematureMerge; // Whether to prematurely merge the input of this operator.
private bool _limitsParallelism; // Whether this operator limits parallelism
//---------------------------------------------------------------------------------------
// Initializes a new select operator.
//
// Arguments:
// child - the child operator or data source from which to pull data
// selector - a delegate representing the selector function
//
// Assumptions:
// selector must be non null.
//
internal IndexedSelectQueryOperator(IEnumerable<TInput> child,
Func<TInput, int, TOutput> selector)
: base(child)
{
Debug.Assert(child != null, "child data source cannot be null");
Debug.Assert(selector != null, "need a selector function");
_selector = selector;
// In an indexed Select, elements must be returned in the order in which
// indices were assigned.
_outputOrdered = true;
InitOrdinalIndexState();
}
private void InitOrdinalIndexState()
{
OrdinalIndexState childIndexState = Child.OrdinalIndexState;
OrdinalIndexState indexState = childIndexState;
if (ExchangeUtilities.IsWorseThan(childIndexState, OrdinalIndexState.Correct))
{
_prematureMerge = true;
_limitsParallelism = childIndexState != OrdinalIndexState.Shuffled;
indexState = OrdinalIndexState.Correct;
}
Debug.Assert(!ExchangeUtilities.IsWorseThan(indexState, OrdinalIndexState.Correct));
SetOrdinalIndexState(indexState);
}
//---------------------------------------------------------------------------------------
// Just opens the current operator, including opening the child and wrapping it with
// partitions as needed.
//
internal override QueryResults<TOutput> Open(
QuerySettings settings, bool preferStriping)
{
QueryResults<TInput> childQueryResults = Child.Open(settings, preferStriping);
return IndexedSelectQueryOperatorResults.NewResults(childQueryResults, this, settings, preferStriping);
}
internal override void WrapPartitionedStream<TKey>(
PartitionedStream<TInput, TKey> inputStream, IPartitionedStreamRecipient<TOutput> recipient, bool preferStriping, QuerySettings settings)
{
int partitionCount = inputStream.PartitionCount;
// If the index is not correct, we need to reindex.
PartitionedStream<TInput, int> inputStreamInt;
if (_prematureMerge)
{
ListQueryResults<TInput> listResults = QueryOperator<TInput>.ExecuteAndCollectResults(
inputStream, partitionCount, Child.OutputOrdered, preferStriping, settings);
inputStreamInt = listResults.GetPartitionedStream();
}
else
{
Debug.Assert(typeof(TKey) == typeof(int));
inputStreamInt = (PartitionedStream<TInput, int>)(object)inputStream;
}
// Since the index is correct, the type of the index must be int
PartitionedStream<TOutput, int> outputStream =
new PartitionedStream<TOutput, int>(partitionCount, Util.GetDefaultComparer<int>(), OrdinalIndexState);
for (int i = 0; i < partitionCount; i++)
{
outputStream[i] = new IndexedSelectQueryOperatorEnumerator(inputStreamInt[i], _selector);
}
recipient.Receive(outputStream);
}
//---------------------------------------------------------------------------------------
// Whether this operator performs a premature merge that would not be performed in
// a similar sequential operation (i.e., in LINQ to Objects).
//
internal override bool LimitsParallelism
{
get { return _limitsParallelism; }
}
//---------------------------------------------------------------------------------------
// The enumerator type responsible for projecting elements as it is walked.
//
private sealed class IndexedSelectQueryOperatorEnumerator : QueryOperatorEnumerator<TOutput, int>
{
private readonly QueryOperatorEnumerator<TInput, int> _source; // The data source to enumerate.
private readonly Func<TInput, int, TOutput> _selector; // The actual select function.
//---------------------------------------------------------------------------------------
// Instantiates a new select enumerator.
//
internal IndexedSelectQueryOperatorEnumerator(QueryOperatorEnumerator<TInput, int> source, Func<TInput, int, TOutput> selector)
{
Debug.Assert(source != null);
Debug.Assert(selector != null);
_source = source;
_selector = selector;
}
//---------------------------------------------------------------------------------------
// Straightforward IEnumerator<T> methods.
//
internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TOutput currentElement, ref int currentKey)
{
// So long as the source has a next element, we have an element.
TInput element = default(TInput)!;
if (_source.MoveNext(ref element!, ref currentKey))
{
Debug.Assert(_selector != null, "expected a compiled selection function");
currentElement = _selector(element, currentKey);
return true;
}
return false;
}
protected override void Dispose(bool disposing)
{
_source.Dispose();
}
}
//---------------------------------------------------------------------------------------
// Returns an enumerable that represents the query executing sequentially.
//
internal override IEnumerable<TOutput> AsSequentialQuery(CancellationToken token)
{
return Child.AsSequentialQuery(token).Select(_selector);
}
//-----------------------------------------------------------------------------------
// Query results for an indexed Select operator. The results are indexable if the child
// results were indexable.
//
private sealed class IndexedSelectQueryOperatorResults : UnaryQueryOperatorResults
{
private readonly IndexedSelectQueryOperator<TInput, TOutput> _selectOp; // Operator that generated the results
private readonly int _childCount; // The number of elements in child results
public static QueryResults<TOutput> NewResults(
QueryResults<TInput> childQueryResults, IndexedSelectQueryOperator<TInput, TOutput> op,
QuerySettings settings, bool preferStriping)
{
if (childQueryResults.IsIndexible)
{
return new IndexedSelectQueryOperatorResults(
childQueryResults, op, settings, preferStriping);
}
else
{
return new UnaryQueryOperatorResults(
childQueryResults, op, settings, preferStriping);
}
}
private IndexedSelectQueryOperatorResults(
QueryResults<TInput> childQueryResults, IndexedSelectQueryOperator<TInput, TOutput> op,
QuerySettings settings, bool preferStriping)
: base(childQueryResults, op, settings, preferStriping)
{
_selectOp = op;
Debug.Assert(_childQueryResults.IsIndexible);
_childCount = _childQueryResults.ElementsCount;
}
internal override int ElementsCount
{
get
{
Debug.Assert(_childCount >= 0);
return _childQueryResults.ElementsCount;
}
}
internal override bool IsIndexible
{
get { return true; }
}
internal override TOutput GetElement(int index)
{
return _selectOp._selector(_childQueryResults.GetElement(index), index);
}
}
}
}
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