ReverseQueryOperator.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Unary / ReverseQueryOperator.cs / 1305376 / ReverseQueryOperator.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// ReverseQueryOperator.cs 
//
// [....] 
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// Reverse imposes ordinal order preservation. There are normally two phases to this
    /// operator's execution.  Each partition first builds a buffer containing all of its
    /// elements, and then proceeds to yielding the elements in reverse.  There is a 
    /// 'barrier' (but not a blocking barrier) in between these two steps, at which point the largest index becomes
    /// known.  This is necessary so that when elements from the buffer are yielded, the 
    /// CurrentIndex can be reported as the largest index minus the original index (thereby 
    /// reversing the indices as well as the elements themselves).  If the largest index is
    /// known a priori, because we have an array for example, we can avoid the barrier in 
    /// between the steps.
    /// 
    /// 
    internal sealed class ReverseQueryOperator : UnaryQueryOperator 
    {
 
        //---------------------------------------------------------------------------------------- 
        // Initializes a new reverse operator.
        // 
        // Arguments:
        //     child                - the child whose data we will reverse
        //
 
        internal ReverseQueryOperator(IEnumerable child)
            :base(child) 
        { 
            Contract.Assert(child != null, "child data source cannot be null");
 
            if (Child.OrdinalIndexState == OrdinalIndexState.Indexible)
            {
                SetOrdinalIndexState(OrdinalIndexState.Indexible);
            } 
            else
            { 
                SetOrdinalIndexState(OrdinalIndexState.Shuffled); 
            }
 
        }

        internal override void WrapPartitionedStream(
            PartitionedStream inputStream, IPartitionedStreamRecipient recipient, bool preferStriping, QuerySettings settings) 
        {
            Contract.Assert(Child.OrdinalIndexState != OrdinalIndexState.Indexible, "Don't take this code path if the child is indexible."); 
 
            int partitionCount = inputStream.PartitionCount;
            PartitionedStream outputStream = new PartitionedStream( 
                partitionCount, new ReverseComparer(inputStream.KeyComparer), OrdinalIndexState.Shuffled);

            for (int i = 0; i < partitionCount; i++)
            { 
                outputStream[i] = new ReverseQueryOperatorEnumerator(inputStream[i], settings.CancellationState.MergedCancellationToken);
            } 
            recipient.Receive(outputStream); 
        }
 
        //---------------------------------------------------------------------------------------
        // Just opens the current operator, including opening the child and wrapping it with
        // partitions as needed.
        // 

        internal override QueryResults Open(QuerySettings settings, bool preferStriping) 
        { 
            QueryResults childQueryResults = Child.Open(settings, false);
            return ReverseQueryOperatorResults.NewResults(childQueryResults, this, settings, preferStriping); 
        }

        //---------------------------------------------------------------------------------------
        // 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.Reverse();
        }

        //--------------------------------------------------------------------------------------- 
        // Whether this operator performs a premature merge.
        // 
 
        internal override bool LimitsParallelism
        { 
            get { return false; }
        }

        //---------------------------------------------------------------------------------------- 
        // The enumerator type responsible for executing the reverse operation.
        // 
 
        class ReverseQueryOperatorEnumerator : QueryOperatorEnumerator
        { 

            private readonly QueryOperatorEnumerator m_source; // The data source to reverse.
            private readonly CancellationToken m_cancellationToken;
            private List> m_buffer; // Our buffer. [allocate in moveNext to avoid false-sharing] 
            private Shared m_bufferIndex; // Our current index within the buffer. [allocate in moveNext to avoid false-sharing]
 
            //--------------------------------------------------------------------------------------- 
            // Instantiates a new select enumerator.
            // 

            internal ReverseQueryOperatorEnumerator(QueryOperatorEnumerator source,
                CancellationToken cancellationToken)
            { 
                Contract.Assert(source != null);
                m_source = source; 
                m_cancellationToken = cancellationToken; 
            }
 
            //----------------------------------------------------------------------------------------
            // Straightforward IEnumerator methods.
            //
 
            internal override bool MoveNext(ref TSource currentElement, ref TKey currentKey)
            { 
                // If the buffer has not been created, we will generate it lazily on demand. 
                if (m_buffer == null)
                { 
                    m_bufferIndex = new Shared(0);
                    // Buffer all of our data.
                    m_buffer = new List>();
                    TSource current = default(TSource); 
                    TKey key = default(TKey);
                    int i = 0; 
                    while (m_source.MoveNext(ref current, ref key)) 
                    {
                        if ((i++ & CancellationState.POLL_INTERVAL) == 0) 
                            CancellationState.ThrowIfCanceled(m_cancellationToken);

                        m_buffer.Add(new Pair(current, key));
                        m_bufferIndex.Value++; 
                    }
                } 
 
                // Continue yielding elements from our buffer.
                if (--m_bufferIndex.Value >= 0) 
                {
                    currentElement = m_buffer[m_bufferIndex.Value].First;
                    currentKey = m_buffer[m_bufferIndex.Value].Second;
                    return true; 
                }
 
                return false; 
            }
 
            protected override void Dispose(bool disposing)
            {
                m_source.Dispose();
            } 
        }
 
        //------------------------------------------------------------------------------------ 
        // Query results for a Reverse operator. The results are indexible if the child
        // results were indexible. 
        //

        class ReverseQueryOperatorResults : UnaryQueryOperatorResults
        { 
            private int m_count; // The number of elements in child results
 
            public static QueryResults NewResults( 
                QueryResults childQueryResults, ReverseQueryOperator op,
                QuerySettings settings, bool preferStriping) 
            {
                if (childQueryResults.IsIndexible)
                {
                    return new ReverseQueryOperatorResults( 
                        childQueryResults, op, settings, preferStriping);
                } 
                else 
                {
                    return new UnaryQueryOperatorResults( 
                        childQueryResults, op, settings, preferStriping);
                }
            }
 
            private ReverseQueryOperatorResults(
                QueryResults childQueryResults, ReverseQueryOperator op, 
                QuerySettings settings, bool preferStriping) 
                : base(childQueryResults, op, settings, preferStriping)
            { 
                Contract.Assert(m_childQueryResults.IsIndexible);
                m_count = m_childQueryResults.ElementsCount;
            }
 
            internal override bool IsIndexible
            { 
                get { return true; } 
            }
 
            internal override int ElementsCount
            {
                get
                { 
                    Contract.Assert(m_count >= 0);
                    return m_count; 
                } 
            }
 
            internal override TSource GetElement(int index)
            {
                Contract.Assert(m_count >= 0);
                Contract.Assert(index >= 0); 
                Contract.Assert(index < m_count);
 
                return m_childQueryResults.GetElement(m_count - index - 1); 
            }
        } 

    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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ReverseQueryOperator.cs source code in C# .NET

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