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// ==++==
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
// ==--==
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// ContainsSearchOperator.cs
//
// <OWNER>Microsoft</OWNER>
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Threading;
namespace System.Linq.Parallel
{
/// <summary>
/// Contains is quite similar to the any/all operator above. Each partition searches a
/// subset of elements for a match, and the first one to find a match signals to the rest
/// of the partititons to stop searching.
/// </summary>
/// <typeparam name="TInput"></typeparam>
internal sealed class ContainsSearchOperator<TInput> : UnaryQueryOperator<TInput, bool>
{
private readonly TInput m_searchValue; // The value for which we are searching.
private readonly IEqualityComparer<TInput> m_comparer; // The comparer to use for equality tests.
//---------------------------------------------------------------------------------------
// Constructs a new instance of the contains search operator.
//
// Arguments:
// child - the child tree to enumerate.
// searchValue - value we are searching for.
// comparer - a comparison routine used to test equality.
//
internal ContainsSearchOperator(IEnumerable<TInput> child, TInput searchValue, IEqualityComparer<TInput> comparer)
:base(child)
{
Contract.Assert(child != null, "child data source cannot be null");
m_searchValue = searchValue;
if (comparer == null)
{
m_comparer = EqualityComparer<TInput>.Default;
}
else
{
m_comparer = comparer;
}
}
//---------------------------------------------------------------------------------------
// Executes the entire query tree, and aggregates the individual partition results to
// form an overall answer to the search operation.
//
internal bool Aggregate()
{
// Because the final reduction is typically much cheaper than the intermediate
// reductions over the individual partitions, and because each parallel partition
// could 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<bool> enumerator = GetEnumerator(ParallelMergeOptions.FullyBuffered, true))
{
// Any value of true means the element was found. We needn't consult all partitions
while (enumerator.MoveNext())
{
if (enumerator.Current)
{
return true;
}
}
}
return false;
}
//---------------------------------------------------------------------------------------
// Just opens the current operator, including opening the child and wrapping it with
// partitions as needed.
//
internal override QueryResults<bool> Open(QuerySettings settings, bool preferStriping)
{
QueryResults<TInput> childQueryResults = Child.Open(settings, preferStriping);
return new UnaryQueryOperatorResults(childQueryResults, this, settings, preferStriping);
}
internal override void WrapPartitionedStream<TKey>(
PartitionedStream<TInput, TKey> inputStream, IPartitionedStreamRecipient<bool> recipient, bool preferStriping, QuerySettings settings)
{
int partitionCount = inputStream.PartitionCount;
PartitionedStream<bool, int> outputStream = new PartitionedStream<bool, int>(partitionCount, Util.GetDefaultComparer<int>(), OrdinalIndexState.Correct);
// Create a shared cancelation variable
Shared<bool> resultFoundFlag = new Shared<bool>(false);
for (int i = 0; i < partitionCount; i++)
{
outputStream[i] = new ContainsSearchOperatorEnumerator<TKey>(inputStream[i], m_searchValue, m_comparer, i, resultFoundFlag,
settings.CancellationState.MergedCancellationToken);
}
recipient.Receive(outputStream);
}
//---------------------------------------------------------------------------------------
// Returns an enumerable that represents the query executing sequentially.
//
internal override IEnumerable<bool> AsSequentialQuery(CancellationToken token)
{
Contract.Assert(false, "This method should never be called as it is an ending operator with LimitsParallelism=false.");
throw new NotSupportedException();
}
//---------------------------------------------------------------------------------------
// 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 false; }
}
//---------------------------------------------------------------------------------------
// This enumerator performs the search over its input data source. It also cancels peer
// enumerators when an answer was found, and polls this cancelation flag to stop when
// requested.
//
class ContainsSearchOperatorEnumerator<TKey> : QueryOperatorEnumerator<bool, int>
{
private readonly QueryOperatorEnumerator<TInput, TKey> m_source; // The source data.
private readonly TInput m_searchValue; // The value for which we are searching.
private readonly IEqualityComparer<TInput> m_comparer; // The comparer to use for equality tests.
private readonly int m_partitionIndex; // This partition's unique index.
private readonly Shared<bool> m_resultFoundFlag; // Whether to cancel the operation.
private CancellationToken m_cancellationToken;
//---------------------------------------------------------------------------------------
// Instantiates a new any/all search operator.
//
internal ContainsSearchOperatorEnumerator(QueryOperatorEnumerator<TInput, TKey> source, TInput searchValue,
IEqualityComparer<TInput> comparer, int partitionIndex, Shared<bool> resultFoundFlag,
CancellationToken cancellationToken)
{
Contract.Assert(source != null);
Contract.Assert(comparer != null);
Contract.Assert(resultFoundFlag != null);
m_source = source;
m_searchValue = searchValue;
m_comparer = comparer;
m_partitionIndex = partitionIndex;
m_resultFoundFlag = resultFoundFlag;
m_cancellationToken = cancellationToken;
}
//---------------------------------------------------------------------------------------
// This enumerates the entire input source to perform the search. If another peer
// partition finds an answer before us, we will voluntarily return (propagating the
// peer's result).
//
internal override bool MoveNext(ref bool currentElement, ref int currentKey)
{
Contract.Assert(m_comparer != null);
// Avoid enumerating if we've already found an answer.
if (m_resultFoundFlag.Value)
return false;
// We just scroll through the enumerator and accumulate the result.
TInput element = default(TInput);
TKey keyUnused = default(TKey);
if (m_source.MoveNext(ref element, ref keyUnused))
{
currentElement = false;
currentKey = m_partitionIndex;
// Continue walking the data so long as we haven't found an item that satisfies
// the condition we are searching for.
int i = 0;
do
{
if ((i++ & CancellationState.POLL_INTERVAL) == 0)
CancellationState.ThrowIfCanceled(m_cancellationToken);
if (m_resultFoundFlag.Value)
{
// If cancelation occurred, it's because a successful answer was found.
return false;
}
if (m_comparer.Equals(element, m_searchValue))
{
// We have found an item that satisfies the search. Cancel other
// workers that are concurrently searching, and return.
m_resultFoundFlag.Value = true;
currentElement = true;
break;
}
}
while (m_source.MoveNext(ref element, ref keyUnused));
return true;
}
return false;
}
protected override void Dispose(bool disposing)
{
Contract.Assert(m_source != null);
m_source.Dispose();
}
}
}
}
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