Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Binary / HashJoinQueryOperatorEnumerator.cs / 1305376 / HashJoinQueryOperatorEnumerator.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // HashJoinQueryOperatorEnumerator.cs // //[....] // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections.Generic; using System.Diagnostics.Contracts; using System.Threading; namespace System.Linq.Parallel { ////// This enumerator implements the hash-join algorithm as noted earlier. /// /// Assumptions: /// This enumerator type won't work properly at all if the analysis engine didn't /// ensure a proper hash-partition. We expect inner and outer elements with equal /// keys are ALWAYS in the same partition. If they aren't (e.g. if the analysis is /// busted) we'll silently drop items on the floor. :( /// /// /// This is the enumerator class for two operators: /// - Join /// - GroupJoin /// ////// /// /// /// internal class HashJoinQueryOperatorEnumerator : QueryOperatorEnumerator { private readonly QueryOperatorEnumerator , TLeftKey> m_leftSource; // Left (outer) data source. For probing. private readonly QueryOperatorEnumerator , int> m_rightSource; // Right (inner) data source. For building. private readonly Func m_singleResultSelector; // Single result selector. private readonly Func , TOutput> m_groupResultSelector; // Group result selector. private readonly IEqualityComparer m_keyComparer; // An optional key comparison object. private readonly CancellationToken m_cancellationToken; private Mutables m_mutables; private class Mutables { internal TLeftInput m_currentLeft; // The current matching left element. internal TLeftKey m_currentLeftKey; // The current index of the matching left element. internal HashLookup >> m_rightHashLookup; // The hash lookup. internal ListChunk m_currentRightMatches; // Current right matches (if any). internal int m_currentRightMatchesIndex; // Current index in the set of right matches. internal int m_outputLoopCount; } //---------------------------------------------------------------------------------------- // Instantiates a new hash-join enumerator. // internal HashJoinQueryOperatorEnumerator( QueryOperatorEnumerator , TLeftKey> leftSource, QueryOperatorEnumerator , int> rightSource, Func singleResultSelector, Func , TOutput> groupResultSelector, IEqualityComparer keyComparer, CancellationToken cancellationToken) { Contract.Assert(leftSource != null); Contract.Assert(rightSource != null); Contract.Assert(singleResultSelector != null || groupResultSelector != null); m_leftSource = leftSource; m_rightSource = rightSource; m_singleResultSelector = singleResultSelector; m_groupResultSelector = groupResultSelector; m_keyComparer = keyComparer; m_cancellationToken = cancellationToken; } //--------------------------------------------------------------------------------------- // MoveNext implements all the hash-join logic noted earlier. When it is called first, it // will execute the entire inner query tree, and build a hash-table lookup. This is the // Building phase. Then for the first call and all subsequent calls to MoveNext, we will // incrementally perform the Probing phase. We'll keep getting elements from the outer // data source, looking into the hash-table we built, and enumerating the full results. // // This routine supports both inner and outer (group) joins. An outer join will yield a // (possibly empty) list of matching elements from the inner instead of one-at-a-time, // as we do for inner joins. // internal override bool MoveNext(ref TOutput currentElement, ref TLeftKey currentKey) { Contract.Assert(m_singleResultSelector != null || m_groupResultSelector != null, "expected a compiled result selector"); Contract.Assert(m_leftSource != null); Contract.Assert(m_rightSource != null); // BUILD phase: If we haven't built the hash-table yet, create that first. Mutables mutables = m_mutables; if (mutables == null) { mutables = m_mutables = new Mutables(); #if DEBUG int hashLookupCount = 0; int hashKeyCollisions = 0; #endif mutables.m_rightHashLookup = new HashLookup >>(m_keyComparer); Pair rightPair = default(Pair ); int rightKeyUnused = default(int); int i = 0; while (m_rightSource.MoveNext(ref rightPair, ref rightKeyUnused)) { if ((i++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); TRightInput rightElement = rightPair.First; THashKey rightHashKey = rightPair.Second; // We ignore null keys. if (rightHashKey != null) { #if DEBUG hashLookupCount++; #endif // See if we've already stored an element under the current key. If not, we // lazily allocate a pair to hold the elements mapping to the same key. const int INITIAL_CHUNK_SIZE = 2; Pair > currentValue = default(Pair >); if (!mutables.m_rightHashLookup.TryGetValue(rightHashKey, ref currentValue)) { currentValue = new Pair >(rightElement, null); if (m_groupResultSelector != null) { // For group joins, we also add the element to the list. This makes // it easier later to yield the list as-is. currentValue.Second = new ListChunk (INITIAL_CHUNK_SIZE); currentValue.Second.Add(rightElement); } mutables.m_rightHashLookup.Add(rightHashKey, currentValue); } else { if (currentValue.Second == null) { // Lazily allocate a list to hold all but the 1st value. We need to // re-store this element because the pair is a value type. currentValue.Second = new ListChunk (INITIAL_CHUNK_SIZE); mutables.m_rightHashLookup[rightHashKey] = currentValue; } currentValue.Second.Add(rightElement); #if DEBUG hashKeyCollisions++; #endif } } } #if DEBUG TraceHelpers.TraceInfo("ParallelJoinQueryOperator::MoveNext - built hash table [count = {0}, collisions = {1}]", hashLookupCount, hashKeyCollisions); #endif } // PROBE phase: So long as the source has a next element, return the match. ListChunk currentRightChunk = mutables.m_currentRightMatches; if (currentRightChunk != null && mutables.m_currentRightMatchesIndex == currentRightChunk.Count) { currentRightChunk = mutables.m_currentRightMatches = currentRightChunk.Next; mutables.m_currentRightMatchesIndex = 0; } if (mutables.m_currentRightMatches == null) { // We have to look up the next list of matches in the hash-table. Pair leftPair = default(Pair ); TLeftKey leftKey = default(TLeftKey); while (m_leftSource.MoveNext(ref leftPair, ref leftKey)) { if ((mutables.m_outputLoopCount++ & CancellationState.POLL_INTERVAL) == 0) CancellationState.ThrowIfCanceled(m_cancellationToken); // Find the match in the hash table. Pair > matchValue = default(Pair >); TLeftInput leftElement = leftPair.First; THashKey leftHashKey = leftPair.Second; // Ignore null keys. if (leftHashKey != null) { if (mutables.m_rightHashLookup.TryGetValue(leftHashKey, ref matchValue)) { // We found a new match. For inner joins, we remember the list in case // there are multiple value under this same key -- the next iteration will pick // them up. For outer joins, we will use the list momentarily. if (m_singleResultSelector != null) { mutables.m_currentRightMatches = matchValue.Second; Contract.Assert(mutables.m_currentRightMatches == null || mutables.m_currentRightMatches.Count > 0, "we were expecting that the list would be either null or empty"); mutables.m_currentRightMatchesIndex = 0; // Yield the value. currentElement = m_singleResultSelector(leftElement, matchValue.First); currentKey = leftKey; // If there is a list of matches, remember the left values for next time. if (matchValue.Second != null) { mutables.m_currentLeft = leftElement; mutables.m_currentLeftKey = leftKey; } return true; } } } // For outer joins, we always yield a result. if (m_groupResultSelector != null) { // Grab the matches, or create an empty list if there are none. IEnumerable matches = matchValue.Second; if (matches == null) { matches = ParallelEnumerable.Empty (); } // Generate the current value. currentElement = m_groupResultSelector(leftElement, matches); currentKey = leftKey; return true; } } // If we've reached the end of the data source, we're done. return false; } // Produce the next element and increment our index within the matches. Contract.Assert(m_singleResultSelector != null); Contract.Assert(mutables.m_currentRightMatches != null); Contract.Assert(0 <= mutables.m_currentRightMatchesIndex && mutables.m_currentRightMatchesIndex < mutables.m_currentRightMatches.Count); currentElement = m_singleResultSelector( mutables.m_currentLeft, mutables.m_currentRightMatches.m_chunk[mutables.m_currentRightMatchesIndex]); currentKey = mutables.m_currentLeftKey; mutables.m_currentRightMatchesIndex++; return true; } protected override void Dispose(bool disposing) { Contract.Assert(m_leftSource != null && m_rightSource != null); m_leftSource.Dispose(); m_rightSource.Dispose(); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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