DistinctQueryOperator.cs source code in C# .NET

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Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Unary / DistinctQueryOperator.cs / 1305376 / DistinctQueryOperator.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// DistinctQueryOperator.cs 
//
// [....] 
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// This operator yields all of the distinct elements in a single data set. It works quite
    /// like the above set operations, with the obvious difference being that it only accepts
    /// a single data source as input. 
    /// 
    ///  
    internal sealed class DistinctQueryOperator : UnaryQueryOperator 
    {
 
        private readonly IEqualityComparer m_comparer; // An (optional) equality comparer.

        //----------------------------------------------------------------------------------------
        // Constructs a new distinction operator. 
        //
 
        internal DistinctQueryOperator(IEnumerable source, IEqualityComparer comparer) 
            :base(source)
        { 
            Contract.Assert(source != null, "child data source cannot be null");
            m_comparer = comparer;
            SetOrdinalIndexState(OrdinalIndexState.Shuffled);
        } 

        //--------------------------------------------------------------------------------------- 
        // Just opens the current operator, including opening the child and wrapping it with 
        // partitions as needed.
        // 

        internal override QueryResults Open(QuerySettings settings, bool preferStriping)
        {
            // We just open our child operator.  Do not propagate the preferStriping value, but 
            // instead explicitly set it to false. Regardless of whether the parent prefers striping or range
            // partitioning, the output will be hash-partititioned. 
            QueryResults childResults = Child.Open(settings, false); 
            return new UnaryQueryOperatorResults(childResults, this, settings, false);
        } 

        internal override void WrapPartitionedStream(
            PartitionedStream inputStream, IPartitionedStreamRecipient recipient, bool preferStriping, QuerySettings settings)
        { 
            // Hash-repartion the source stream
            if (OutputOrdered) 
            { 
                WrapPartitionedStreamHelper(
                    ExchangeUtilities.HashRepartitionOrdered( 
                        inputStream, null, null, m_comparer, settings.CancellationState.MergedCancellationToken),
                    recipient, settings.CancellationState.MergedCancellationToken);
            }
            else 
            {
                WrapPartitionedStreamHelper( 
                    ExchangeUtilities.HashRepartition( 
                        inputStream, null, null, m_comparer, settings.CancellationState.MergedCancellationToken),
                    recipient, settings.CancellationState.MergedCancellationToken); 
            }
        }

        //--------------------------------------------------------------------------------------- 
        // This is a helper method. WrapPartitionedStream decides what type TKey is going
        // to be, and then call this method with that key as a generic parameter. 
        // 

        private void WrapPartitionedStreamHelper( 
            PartitionedStream, TKey> hashStream,
            IPartitionedStreamRecipient recipient, CancellationToken cancellationToken)
        {
            int partitionCount = hashStream.PartitionCount; 
            PartitionedStream outputStream =
                new PartitionedStream(partitionCount, hashStream.KeyComparer, OrdinalIndexState.Shuffled); 
 
            for (int i = 0; i < partitionCount; i++)
            { 
                if (OutputOrdered)
                {
                    outputStream[i] =
                        new OrderedDistinctQueryOperatorEnumerator(hashStream[i], m_comparer, hashStream.KeyComparer, cancellationToken); 
                }
                else 
                { 
                    outputStream[i] = (QueryOperatorEnumerator)(object)
                                                                                   new DistinctQueryOperatorEnumerator(hashStream[i], m_comparer, cancellationToken); 
                }
            }

            recipient.Receive(outputStream); 
        }
 
        //--------------------------------------------------------------------------------------- 
        // Whether this operator performs a premature merge.
        // 

        internal override bool LimitsParallelism
        {
            get { return false; } 
        }
 
        //---------------------------------------------------------------------------------------- 
        // This enumerator performs the distinct operation incrementally. It does this by
        // maintaining a history -- in the form of a set -- of all data already seen. It simply 
        // then doesn't return elements it has already seen before.
        //

        class DistinctQueryOperatorEnumerator : QueryOperatorEnumerator 
        {
 
            private QueryOperatorEnumerator, TKey> m_source; // The data source. 
            private Set m_hashLookup; // The hash lookup, used to produce the distinct set.
            private CancellationToken m_cancellationToken; 
            private Shared m_outputLoopCount; // Allocated in MoveNext to avoid false sharing.

            //---------------------------------------------------------------------------------------
            // Instantiates a new distinction operator. 
            //
 
            internal DistinctQueryOperatorEnumerator( 
                QueryOperatorEnumerator, TKey> source, IEqualityComparer comparer,
                CancellationToken cancellationToken) 
            {
                Contract.Assert(source != null);
                m_source = source;
                // @ 
                m_hashLookup = new Set(comparer);
                m_cancellationToken = cancellationToken; 
            } 

            //---------------------------------------------------------------------------------------- 
            // Walks the single data source, skipping elements it has already seen.
            //

            internal override bool MoveNext(ref TInputOutput currentElement, ref int currentKey) 
            {
                Contract.Assert(m_source != null); 
                Contract.Assert(m_hashLookup != null); 

                // Iterate over this set's elements until we find a unique element. 
                TKey keyUnused = default(TKey);
                Pair current = default(Pair);

                if (m_outputLoopCount == null) 
                    m_outputLoopCount = new Shared(0);
 
                while (m_source.MoveNext(ref current, ref keyUnused)) 
                {
                    if ((m_outputLoopCount.Value++ & CancellationState.POLL_INTERVAL) == 0) 
                        CancellationState.ThrowIfCanceled(m_cancellationToken);

                    // We ensure we never return duplicates by tracking them in our set.
                    if (m_hashLookup.Add(current.First)) 
                    {
#if DEBUG 
                        currentKey = unchecked((int)0xdeadbeef); 
#endif
                        currentElement = current.First; 
                        return true;
                    }
                }
 
                return false;
            } 
 
            protected override void Dispose(bool disposing)
            { 
                Contract.Assert(m_source != null);
                m_source.Dispose();
            }
        } 

        //---------------------------------------------------------------------------------------- 
        // Returns an enumerable that represents the query executing sequentially. 
        //
 
        internal override IEnumerable AsSequentialQuery(CancellationToken token)
        {
            IEnumerable wrappedChild = CancellableEnumerable.Wrap(Child.AsSequentialQuery(token), token);
            return wrappedChild.Distinct(m_comparer); 
        }
 
        class OrderedDistinctQueryOperatorEnumerator : QueryOperatorEnumerator 
        {
 
            private QueryOperatorEnumerator, TKey> m_source; // The data source.
            private Dictionary, TKey> m_hashLookup; // The hash lookup, used to produce the distinct set.
            private IComparer m_keyComparer; // Comparer to decide the key order.
            private IEnumerator, TKey>> m_hashLookupEnumerator; // Enumerates over m_hashLookup. 
            private CancellationToken m_cancellationToken;
 
            //--------------------------------------------------------------------------------------- 
            // Instantiates a new distinction operator.
            // 

            internal OrderedDistinctQueryOperatorEnumerator(
                QueryOperatorEnumerator, TKey> source,
                IEqualityComparer comparer, IComparer keyComparer, 
                CancellationToken cancellationToken)
            { 
                Contract.Assert(source != null); 
                m_source = source;
                m_keyComparer = keyComparer; 

                // @
                m_hashLookup = new Dictionary, TKey>(
                    new WrapperEqualityComparer(comparer)); 

                m_cancellationToken = cancellationToken; 
            } 

            //---------------------------------------------------------------------------------------- 
            // Walks the single data source, skipping elements it has already seen.
            //

            internal override bool MoveNext(ref TInputOutput currentElement, ref TKey currentKey) 
            {
                Contract.Assert(m_source != null); 
                Contract.Assert(m_hashLookup != null); 

                if (m_hashLookupEnumerator == null) 
                {
                    Pair elem = default(Pair);
                    TKey orderKey = default(TKey);
 
                    int i = 0;
                    while (m_source.MoveNext(ref elem, ref orderKey)) 
                    { 
                        if ((i++ & CancellationState.POLL_INTERVAL) == 0)
                            CancellationState.ThrowIfCanceled(m_cancellationToken); 

                        // For each element, we track the smallest order key for that element that we saw so far
                        TKey oldEntry;
 
                        Wrapper wrappedElem = new Wrapper(elem.First);
 
                        // If this is the first occurence of this element, or the order key is lower than all keys we saw previously, 
                        // update the order key for this element.
                        if (!m_hashLookup.TryGetValue(wrappedElem, out oldEntry) || m_keyComparer.Compare(orderKey, oldEntry) < 0) 
                        {
                            // For each "elem" value, we store the smallest key, and the element value that had that key.
                            // Note that even though two element values are "equal" according to the EqualityComparer,
                            // we still cannot choose arbitrarily which of the two to yield. 
                            m_hashLookup[wrappedElem] = orderKey;
                        } 
                    } 

                    m_hashLookupEnumerator = m_hashLookup.GetEnumerator(); 
                }

                if (m_hashLookupEnumerator.MoveNext())
                { 
                    KeyValuePair, TKey> currentPair = m_hashLookupEnumerator.Current;
                    currentElement = currentPair.Key.Value; 
                    currentKey = currentPair.Value; 
                    return true;
                } 

                return false;
            }
 
            protected override void Dispose(bool disposing)
            { 
                Contract.Assert(m_source != null); 
                m_source.Dispose();
 
                if (m_hashLookupEnumerator != null)
                {
                    m_hashLookupEnumerator.Dispose();
                } 
            }
        } 
 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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