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/ 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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