IndexedSelectQueryOperator.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 / IndexedSelectQueryOperator.cs / 1305376 / IndexedSelectQueryOperator.cs

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

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// 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. 
    ///
    /// @ 
 

 


    internal sealed class IndexedSelectQueryOperator : UnaryQueryOperator
    { 

        // Selector function. Used to project elements to a transformed view during execution. 
        private Func m_selector; 
        private bool m_prematureMerge = false; // Whether to prematurely merge the input of this operator.
 
        //----------------------------------------------------------------------------------------
        // 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 child,
                                            Func selector) 
            :base(child)
        { 
            Contract.Assert(child != null, "child data source cannot be null"); 
            Contract.Assert(selector != null, "need a selector function");
 
            m_selector = selector;

            // In an indexed Select, elements must be returned in the order in which
            // indices were assigned. 
            m_outputOrdered = true;
 
            InitOrdinalIndexState(); 
        }
 
        private void InitOrdinalIndexState()
        {
            OrdinalIndexState indexState = Child.OrdinalIndexState;
 
            if (ExchangeUtilities.IsWorseThan(Child.OrdinalIndexState, OrdinalIndexState.Correct))
            { 
                m_prematureMerge = true; 
                indexState = OrdinalIndexState.Correct;
            } 

            Contract.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 Open(
            QuerySettings settings, bool preferStriping) 
        {
            QueryResults childQueryResults = Child.Open(settings, preferStriping); 
            return IndexedSelectQueryOperatorResults.NewResults(childQueryResults, this, settings, preferStriping); 
        }
 
        internal override void  WrapPartitionedStream(
            PartitionedStream inputStream, IPartitionedStreamRecipient recipient, bool preferStriping, QuerySettings settings)
        {
            int partitionCount = inputStream.PartitionCount; 

            // If the index is not correct, we need to reindex. 
            PartitionedStream inputStreamInt; 
            if (m_prematureMerge)
            { 
                ListQueryResults listResults = QueryOperator.ExecuteAndCollectResults(
                    inputStream, partitionCount, Child.OutputOrdered, preferStriping, settings);
                inputStreamInt = listResults.GetPartitionedStream();
            } 
            else
            { 
                Contract.Assert(typeof(TKey) == typeof(int)); 
                inputStreamInt = (PartitionedStream)(object)inputStream;
            } 

            // Since the index is correct, the type of the index must be int
            PartitionedStream outputStream =
                new PartitionedStream(partitionCount, Util.GetDefaultComparer(), OrdinalIndexState); 

            for (int i = 0; i < partitionCount; i++) 
            { 
                outputStream[i] = new IndexedSelectQueryOperatorEnumerator(inputStreamInt[i], m_selector);
            } 

            recipient.Receive(outputStream);
        }
 

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

        //--------------------------------------------------------------------------------------- 
        // The enumerator type responsible for projecting elements as it is walked. 
        //
 
        class IndexedSelectQueryOperatorEnumerator : QueryOperatorEnumerator
        {

            private readonly QueryOperatorEnumerator m_source; // The data source to enumerate. 
            private readonly Func m_selector;  // The actual select function.
 
            //---------------------------------------------------------------------------------------- 
            // Instantiates a new select enumerator.
            // 

            internal IndexedSelectQueryOperatorEnumerator(QueryOperatorEnumerator source, Func selector)
            {
                Contract.Assert(source != null); 
                Contract.Assert(selector != null);
                m_source = source; 
                m_selector = selector; 
            }
 
            //---------------------------------------------------------------------------------------
            // Straightforward IEnumerator methods.
            //
 
            internal override bool MoveNext(ref TOutput currentElement, ref int currentKey)
            { 
                // So long as the source has a next element, we have an element. 
                TInput element = default(TInput);
                if (m_source.MoveNext(ref element, ref currentKey)) 
                {
                    Contract.Assert(m_selector != null, "expected a compiled selection function");
                    currentElement = m_selector(element, currentKey);
                    return true; 
                }
 
                return false; 
            }
 
            protected override void Dispose(bool disposing)
            {
                m_source.Dispose();
            } 

        } 
 

        //---------------------------------------------------------------------------------------- 
        // Returns an enumerable that represents the query executing sequentially.
        //

        internal override IEnumerable AsSequentialQuery(CancellationToken token) 
        {
            return Child.AsSequentialQuery(token).Select(m_selector); 
        } 

        //------------------------------------------------------------------------------------ 
        // Query results for an indexed Select operator. The results are indexible if the child
        // results were indexible.
        //
 
        class IndexedSelectQueryOperatorResults : UnaryQueryOperatorResults
        { 
            IndexedSelectQueryOperator m_selectOp;  // Operator that generated the results 
            int m_childCount; // The number of elements in child results
 
            public static QueryResults NewResults(
                QueryResults childQueryResults, IndexedSelectQueryOperator 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 childQueryResults, IndexedSelectQueryOperator op, 
                QuerySettings settings, bool preferStriping)
                : base(childQueryResults, op, settings, preferStriping)
            {
                m_selectOp = op; 
                Contract.Assert(m_childQueryResults.IsIndexible);
 
                m_childCount = m_childQueryResults.ElementsCount; 
            }
 
            internal override int ElementsCount
            {
                get
                { 
                    Contract.Assert(m_childCount >= 0);
                    return m_childQueryResults.ElementsCount; 
                } 
            }
 
            internal override bool IsIndexible
            {
                get { return true; }
            } 

            internal override TOutput GetElement(int index) 
            { 
                return m_selectOp.m_selector(m_childQueryResults.GetElement(index), index);
            } 
        }
    }
}

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

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