Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Unary / AnyAllSearchOperator.cs / 1305376 / AnyAllSearchOperator.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // AnyAllSearchOperator.cs // //[....] // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections.Generic; using System.Diagnostics.Contracts; using System.Threading; namespace System.Linq.Parallel { ////// The any/all operators work the same way. They search for the occurrence of a predicate /// value in the data source, and upon the first occurrence of such a value, yield a /// particular value. Specifically: /// /// - Any returns true if the predicate for any element evaluates to true. /// - All returns false if the predicate for any element evaluates to false. /// /// This uniformity is used to apply a general purpose algorithm. Both sentences above /// take the form of "returns XXX if the predicate for any element evaluates to XXX." /// Therefore, we just parameterize on XXX, called the qualifciation below, and if we /// ever find an occurrence of XXX in the input data source, we also return XXX. Otherwise, /// we return !XXX. Obviously, XXX in this case is a bool. /// /// This is a search algorithm. So once any single partition finds an element, it will /// return so that execution can stop. This is done with a "cancelation" flag that is /// polled by all parallel workers. The first worker to find an answer sets it, and all /// other workers notice it and quit as quickly as possible. /// ///internal sealed class AnyAllSearchOperator : UnaryQueryOperator { private readonly Func m_predicate; // The predicate used to test membership. private readonly bool m_qualification; // Whether we're looking for true (any) or false (all). //---------------------------------------------------------------------------------------- // Constructs a new instance of an any/all search operator. // // Arguments: // child - the child tree to enumerate. // qualification - the predicate value we require for an element to be considered // a member of the set; for any this is true, for all it is false. // internal AnyAllSearchOperator(IEnumerable child, bool qualification, Func predicate) :base(child) { Contract.Assert(child != null, "child data source cannot be null"); Contract.Assert(predicate != null, "need a predicate function"); m_qualification = qualification; m_predicate = predicate; } //--------------------------------------------------------------------------------------- // Executes the entire query tree, and aggregates the individual partition results to // form an overall answer to the search operation. // internal bool Aggregate() { // Because the final reduction is typically much cheaper than the intermediate // reductions over the individual partitions, and because each parallel partition // could do a lot of work to produce a single output element, we prefer to turn off // pipelining, and process the final reductions serially. using (IEnumerator enumerator = GetEnumerator(ParallelMergeOptions.FullyBuffered, true)) { // Any value equal to our qualification means that we've found an element matching // the condition, and so we return the qualification without looking in subsequent // partitions. while (enumerator.MoveNext()) { if (enumerator.Current == m_qualification) { return m_qualification; } } } return !m_qualification; } //--------------------------------------------------------------------------------------- // 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 the child operator. QueryResults childQueryResults = Child.Open(settings, preferStriping); return new UnaryQueryOperatorResults(childQueryResults, this, settings, preferStriping); } internal override void WrapPartitionedStream ( PartitionedStream inputStream, IPartitionedStreamRecipient recipient, bool preferStriping, QuerySettings settings) { // Create a shared cancelation variable and then return a possibly wrapped new enumerator. Shared resultFoundFlag = new Shared (false); int partitionCount = inputStream.PartitionCount; PartitionedStream outputStream = new PartitionedStream ( partitionCount, Util.GetDefaultComparer (), OrdinalIndexState.Correct); for (int i = 0; i < partitionCount; i++) { outputStream[i] = new AnyAllSearchOperatorEnumerator (inputStream[i], m_qualification, m_predicate, i, resultFoundFlag, settings.CancellationState.MergedCancellationToken); } 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; } } //--------------------------------------------------------------------------------------- // This enumerator performs the search over its input data source. It also cancels peer // enumerators when an answer was found, and polls this cancelation flag to stop when // requested. // private class AnyAllSearchOperatorEnumerator : QueryOperatorEnumerator { private readonly QueryOperatorEnumerator m_source; // The source data. private readonly Func m_predicate; // The predicate. private readonly bool m_qualification; // Whether this is an any (true) or all (false) operator. private readonly int m_partitionIndex; // The partition's index. private readonly Shared m_resultFoundFlag; // Whether to cancel the search for elements. private readonly CancellationToken m_cancellationToken; //---------------------------------------------------------------------------------------- // Instantiates a new any/all search operator. // internal AnyAllSearchOperatorEnumerator(QueryOperatorEnumerator source, bool qualification, Func predicate, int partitionIndex, Shared resultFoundFlag, CancellationToken cancellationToken) { Contract.Assert(source != null); Contract.Assert(predicate != null); Contract.Assert(resultFoundFlag != null); m_source = source; m_qualification = qualification; m_predicate = predicate; m_partitionIndex = partitionIndex; m_resultFoundFlag = resultFoundFlag; m_cancellationToken = cancellationToken; } //---------------------------------------------------------------------------------------- // This enumerates the entire input source to perform the search. If another peer // partition finds an answer before us, we will voluntarily return (propagating the // peer's result). // internal override bool MoveNext(ref bool currentElement, ref int currentKey) { Contract.Assert(m_predicate != null); // Avoid enumerating if we've already found an answer. if (m_resultFoundFlag.Value) return false; // We just scroll through the enumerator and accumulate the result. TInput element = default(TInput); TKey keyUnused = default(TKey); if (m_source.MoveNext(ref element, ref keyUnused)) { currentElement = !m_qualification; currentKey = m_partitionIndex; int i = 0; // Continue walking the data so long as we haven't found an item that satisfies // the condition we are searching for. do { if ((i++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); if (m_resultFoundFlag.Value) { // If cancelation occurred, it's because a successful answer was found. return false; } if (m_predicate(element) == m_qualification) { // We have found an item that satisfies the search. Tell other // workers that are concurrently searching, and return. m_resultFoundFlag.Value = true; currentElement = m_qualification; break; } } while (m_source.MoveNext(ref element, ref keyUnused)); return true; } return false; } protected override void Dispose(bool disposing) { Contract.Assert(m_source != null); m_source.Dispose(); } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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