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/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Unary / SingleQueryOperator.cs / 1305376 / SingleQueryOperator.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // SingleQueryOperator.cs // //[....] // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections.Generic; using System.Threading; using System.Diagnostics.Contracts; namespace System.Linq.Parallel { ////// Single searches the input to find the sole element that satisfies the (optional) /// predicate. If multiple such elements are found, the caller is responsible for /// producing an error. There is some degree of cross-partition synchronization to /// proactively hault the search if we ever determine there are multiple elements /// satisfying the search in the input. /// ///internal sealed class SingleQueryOperator : UnaryQueryOperator { private readonly Func m_predicate; // The optional predicate used during the search. //---------------------------------------------------------------------------------------- // Initializes a new Single operator. // // Arguments: // child - the child whose data we will reverse // internal SingleQueryOperator(IEnumerable child, Func predicate) :base(child) { Contract.Assert(child != null, "child data source cannot be null"); m_predicate = predicate; } //--------------------------------------------------------------------------------------- // 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 new UnaryQueryOperatorResults(childQueryResults, this, settings, preferStriping); } internal override void WrapPartitionedStream ( PartitionedStream inputStream, IPartitionedStreamRecipient recipient, bool preferStriping, QuerySettings settings) { int partitionCount = inputStream.PartitionCount; PartitionedStream outputStream = new PartitionedStream ( partitionCount, Util.GetDefaultComparer (), OrdinalIndexState.Shuffled); Shared totalElementCount = new Shared (0); for (int i = 0; i < partitionCount; i++) { outputStream[i] = new SingleQueryOperatorEnumerator (inputStream[i], m_predicate, totalElementCount); } recipient.Receive(outputStream); } //--------------------------------------------------------------------------------------- // Returns an enumerable that represents the query executing sequentially. // internal override IEnumerable 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. // internal override bool LimitsParallelism { get { return false; } } //---------------------------------------------------------------------------------------- // The enumerator type responsible for executing the Single operation. // class SingleQueryOperatorEnumerator : QueryOperatorEnumerator { private QueryOperatorEnumerator m_source; // The data source to enumerate. private Func m_predicate; // The optional predicate used during the search. private bool m_alreadySearched; // Whether we have searched our input already. private bool m_yieldExtra; // Whether we found more than one element. // Data shared among partitions. private Shared m_totalElementCount; // The total count of elements found. //--------------------------------------------------------------------------------------- // Instantiates a new enumerator. // internal SingleQueryOperatorEnumerator(QueryOperatorEnumerator source, Func predicate, Shared totalElementCount) { Contract.Assert(source != null); Contract.Assert(totalElementCount != null); m_source = source; m_predicate = predicate; m_totalElementCount = totalElementCount; } //---------------------------------------------------------------------------------------- // Straightforward IEnumerator methods. // internal override bool MoveNext(ref TSource currentElement, ref int currentKey) { Contract.Assert(m_source != null); if (m_alreadySearched) { // If we've already searched, we will "fake out" the caller by returning an extra // element at the end in the case that we've found more than one element. if (m_yieldExtra) { m_yieldExtra = false; currentElement = default(TSource); currentKey = 0; return true; } return false; } // Scan our input, looking for a match. bool found = false; TSource current = default(TSource); TKey keyUnused = default(TKey); while (m_source.MoveNext(ref current, ref keyUnused)) { // If the predicate is null or the current element satisfies it, we will remember // it so that we can yield it later. We then proceed with scanning the input // in case there are multiple such elements. if (m_predicate == null || m_predicate(current)) { // Notify other partitions. Interlocked.Increment(ref m_totalElementCount.Value); currentElement = current; currentKey = 0; if (found) { // Already found an element previously, we can exit. m_yieldExtra = true; break; } else { found = true; } } // If we've already determined there is more than one matching element in the // data source, we can exit right away. if (m_totalElementCount.Value > 1) { break; } } m_alreadySearched = true; return found; } protected override void Dispose(bool disposing) { m_source.Dispose(); } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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