perf: minor improvements to Constraint Streams (#830)

- Iterating manually in join allows to create much less instances of
`Iterator`, reducing GC pressure significantly.
- min/max constraint collector was needlessly using a `Map`, which only
ever had one key.

In cases particularly exposed to these issues, the performance
improvements seen were ~ 10 %.

core/src/main/java/ai/timefold/solver/core/impl/score/stream/bavet/common/AbstractJoinNode.java

@@ -51,12 +51,12 @@ protected AbstractJoinNode(int inputStoreIndexLeftOutTupleList, int inputStoreIn
     protected abstract boolean testFiltering(LeftTuple_ leftTuple, UniTuple<Right_> rightTuple);
 
     protected final void insertOutTuple(LeftTuple_ leftTuple, UniTuple<Right_> rightTuple) {
-        OutTuple_ outTuple = createOutTuple(leftTuple, rightTuple);
+        var outTuple = createOutTuple(leftTuple, rightTuple);
         ElementAwareList<OutTuple_> outTupleListLeft = leftTuple.getStore(inputStoreIndexLeftOutTupleList);
-        ElementAwareListEntry<OutTuple_> outEntryLeft = outTupleListLeft.add(outTuple);
+        var outEntryLeft = outTupleListLeft.add(outTuple);
         outTuple.setStore(outputStoreIndexLeftOutEntry, outEntryLeft);
         ElementAwareList<OutTuple_> outTupleListRight = rightTuple.getStore(inputStoreIndexRightOutTupleList);
-        ElementAwareListEntry<OutTuple_> outEntryRight = outTupleListRight.add(outTuple);
+        var outEntryRight = outTupleListRight.add(outTuple);
         outTuple.setStore(outputStoreIndexRightOutEntry, outEntryRight);
         propagationQueue.insert(outTuple);
     }
@@ -72,7 +72,7 @@ protected final void innerUpdateLeft(LeftTuple_ leftTuple, Consumer<Consumer<Uni
         ElementAwareList<OutTuple_> outTupleListLeft = leftTuple.getStore(inputStoreIndexLeftOutTupleList);
         // Propagate the update for downstream filters, matchWeighers, ...
         if (!isFiltering) {
-            for (OutTuple_ outTuple : outTupleListLeft) {
+            for (var outTuple : outTupleListLeft) {
                 updateOutTupleLeft(outTuple, leftTuple);
             }
         } else {
@@ -89,7 +89,7 @@ private void updateOutTupleLeft(OutTuple_ outTuple, LeftTuple_ leftTuple) {
     }
 
     private void doUpdateOutTuple(OutTuple_ outTuple) {
-        TupleState state = outTuple.state;
+        var state = outTuple.state;
         if (!state.isActive()) { // Impossible because they shouldn't linger in the indexes.
             throw new IllegalStateException("Impossible state: The tuple (" + outTuple.state + ") in node (" +
                     this + ") is in an unexpected state (" + outTuple.state + ").");
@@ -104,7 +104,7 @@ protected final void innerUpdateRight(UniTuple<Right_> rightTuple, Consumer<Cons
         ElementAwareList<OutTuple_> outTupleListRight = rightTuple.getStore(inputStoreIndexRightOutTupleList);
         if (!isFiltering) {
             // Propagate the update for downstream filters, matchWeighers, ...
-            for (OutTuple_ outTuple : outTupleListRight) {
+            for (var outTuple : outTupleListRight) {
                 setOutTupleRightFact(outTuple, rightTuple);
                 doUpdateOutTuple(outTuple);
             }
@@ -118,7 +118,7 @@ protected final void innerUpdateRight(UniTuple<Right_> rightTuple, Consumer<Cons
 
     private void processOutTupleUpdate(LeftTuple_ leftTuple, UniTuple<Right_> rightTuple, ElementAwareList<OutTuple_> outList,
             ElementAwareList<OutTuple_> outTupleList, int outputStoreIndexOutEntry) {
-        OutTuple_ outTuple = findOutTuple(outTupleList, outList, outputStoreIndexOutEntry);
+        var outTuple = findOutTuple(outTupleList, outList, outputStoreIndexOutEntry);
         if (testFiltering(leftTuple, rightTuple)) {
             if (outTuple == null) {
                 insertOutTuple(leftTuple, rightTuple);
@@ -132,15 +132,19 @@ private void processOutTupleUpdate(LeftTuple_ leftTuple, UniTuple<Right_> rightT
         }
     }
 
-    private OutTuple_ findOutTuple(ElementAwareList<OutTuple_> outTupleList, ElementAwareList<OutTuple_> outList,
-            int outputStoreIndexOutEntry) {
+    private static <Tuple_ extends AbstractTuple> Tuple_ findOutTuple(ElementAwareList<Tuple_> outTupleList,
+            ElementAwareList<Tuple_> outList, int outputStoreIndexOutEntry) {
         // Hack: the outTuple has no left/right input tuple reference, use the left/right outList reference instead.
-        for (OutTuple_ outTuple : outTupleList) {
-            ElementAwareListEntry<OutTuple_> outEntry = outTuple.getStore(outputStoreIndexOutEntry);
-            ElementAwareList<OutTuple_> outEntryList = outEntry.getList();
+        var item = outTupleList.first();
+        while (item != null) {
+            // Creating list iterators here caused major GC pressure; therefore, we iterate over the entries directly.
+            var outTuple = item.getElement();
+            ElementAwareListEntry<Tuple_> outEntry = outTuple.getStore(outputStoreIndexOutEntry);
+            var outEntryList = outEntry.getList();
             if (outList == outEntryList) {
                 return outTuple;
             }
+            item = item.next();
         }
         return null;
     }
@@ -150,7 +154,7 @@ protected final void retractOutTuple(OutTuple_ outTuple) {
         outEntryLeft.remove();
         ElementAwareListEntry<OutTuple_> outEntryRight = outTuple.removeStore(outputStoreIndexRightOutEntry);
         outEntryRight.remove();
-        TupleState state = outTuple.state;
+        var state = outTuple.state;
         if (!state.isActive()) {
             // Impossible because they shouldn't linger in the indexes.
             throw new IllegalStateException("Impossible state: The tuple (" + outTuple.state + ") in node (" + this

core/src/main/java/ai/timefold/solver/core/impl/score/stream/bavet/common/index/ComparisonIndexer.java

@@ -12,21 +12,20 @@
 import ai.timefold.solver.core.impl.util.ElementAwareListEntry;
 
 final class ComparisonIndexer<T, Key_ extends Comparable<Key_>>
-        implements ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T> {
+        implements Indexer<T> {
 
     private final int propertyIndex;
-    private final Supplier<ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> downstreamIndexerSupplier;
+    private final Supplier<Indexer<T>> downstreamIndexerSupplier;
     private final Comparator<Key_> keyComparator;
     private final boolean hasOrEquals;
-    private final NavigableMap<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> comparisonMap;
+    private final NavigableMap<Key_, Indexer<T>> comparisonMap;
 
-    public ComparisonIndexer(JoinerType comparisonJoinerType,
-            Supplier<ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> downstreamIndexerSupplier) {
+    public ComparisonIndexer(JoinerType comparisonJoinerType, Supplier<Indexer<T>> downstreamIndexerSupplier) {
         this(comparisonJoinerType, 0, downstreamIndexerSupplier);
     }
 
     public ComparisonIndexer(JoinerType comparisonJoinerType, int propertyIndex,
-            Supplier<ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> downstreamIndexerSupplier) {
+            Supplier<Indexer<T>> downstreamIndexerSupplier) {
         this.propertyIndex = propertyIndex;
         this.downstreamIndexerSupplier = Objects.requireNonNull(downstreamIndexerSupplier);
         /*
@@ -44,11 +43,10 @@ public ComparisonIndexer(JoinerType comparisonJoinerType, int propertyIndex,
     }
 
     @Override
-    public ElementAwareListEntry<T>
-            put(ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties, T tuple) {
+    public ElementAwareListEntry<T> put(IndexProperties indexProperties, T tuple) {
         Key_ indexKey = indexProperties.toKey(propertyIndex);
         // Avoids computeIfAbsent in order to not create lambdas on the hot path.
-        ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T> downstreamIndexer = comparisonMap.get(indexKey);
+        var downstreamIndexer = comparisonMap.get(indexKey);
         if (downstreamIndexer == null) {
             downstreamIndexer = downstreamIndexerSupplier.get();
             comparisonMap.put(indexKey, downstreamIndexer);
@@ -57,22 +55,17 @@ public ComparisonIndexer(JoinerType comparisonJoinerType, int propertyIndex,
     }
 
     @Override
-    public void remove(ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties,
-            ElementAwareListEntry<T> entry) {
+    public void remove(IndexProperties indexProperties, ElementAwareListEntry<T> entry) {
         Key_ indexKey = indexProperties.toKey(propertyIndex);
-        ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T> downstreamIndexer =
-                getDownstreamIndexer(indexProperties, indexKey, entry);
+        var downstreamIndexer = getDownstreamIndexer(indexProperties, indexKey, entry);
         downstreamIndexer.remove(indexProperties, entry);
         if (downstreamIndexer.isEmpty()) {
             comparisonMap.remove(indexKey);
         }
     }
 
-    private ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T> getDownstreamIndexer(
-            ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties, Key_ indexerKey,
-            ElementAwareListEntry<T> entry) {
-        ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T> downstreamIndexer =
-                comparisonMap.get(indexerKey);
+    private Indexer<T> getDownstreamIndexer(IndexProperties indexProperties, Key_ indexerKey, ElementAwareListEntry<T> entry) {
+        var downstreamIndexer = comparisonMap.get(indexerKey);
         if (downstreamIndexer == null) {
             throw new IllegalStateException("Impossible state: the tuple (" + entry.getElement()
                     + ") with indexProperties (" + indexProperties
@@ -83,16 +76,15 @@ private ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>
 
     // TODO clean up DRY
     @Override
-    public int size(ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties) {
-        int mapSize = comparisonMap.size();
+    public int size(IndexProperties indexProperties) {
+        var mapSize = comparisonMap.size();
         if (mapSize == 0) {
             return 0;
         }
         Key_ indexKey = indexProperties.toKey(propertyIndex);
         if (mapSize == 1) { // Avoid creation of the entry set and iterator.
-            Map.Entry<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> entry =
-                    comparisonMap.firstEntry();
-            int comparison = keyComparator.compare(entry.getKey(), indexKey);
+            var entry = comparisonMap.firstEntry();
+            var comparison = keyComparator.compare(entry.getKey(), indexKey);
             if (comparison >= 0) { // Possibility of reaching the boundary condition.
                 if (comparison > 0 || !hasOrEquals) {
                     // Boundary condition reached when we're out of bounds entirely, or when GTE/LTE is not allowed.
@@ -101,10 +93,9 @@ public int size(ai.timefold.solver.core.impl.score.stream.bavet.common.index.Ind
             }
             return entry.getValue().size(indexProperties);
         } else {
-            int size = 0;
-            for (Map.Entry<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> entry : comparisonMap
-                    .entrySet()) {
-                int comparison = keyComparator.compare(entry.getKey(), indexKey);
+            var size = 0;
+            for (var entry : comparisonMap.entrySet()) {
+                var comparison = keyComparator.compare(entry.getKey(), indexKey);
                 if (comparison >= 0) { // Possibility of reaching the boundary condition.
                     if (comparison > 0 || !hasOrEquals) {
                         // Boundary condition reached when we're out of bounds entirely, or when GTE/LTE is not allowed.
@@ -119,33 +110,29 @@ public int size(ai.timefold.solver.core.impl.score.stream.bavet.common.index.Ind
     }
 
     @Override
-    public void forEach(ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties,
-            Consumer<T> tupleConsumer) {
-        int size = comparisonMap.size();
+    public void forEach(IndexProperties indexProperties, Consumer<T> tupleConsumer) {
+        var size = comparisonMap.size();
         if (size == 0) {
             return;
         }
         Key_ indexKey = indexProperties.toKey(propertyIndex);
         if (size == 1) { // Avoid creation of the entry set and iterator.
-            Map.Entry<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> entry =
-                    comparisonMap.firstEntry();
+            var entry = comparisonMap.firstEntry();
             visitEntry(indexProperties, tupleConsumer, indexKey, entry);
         } else {
-            for (Map.Entry<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> entry : comparisonMap
-                    .entrySet()) {
-                boolean boundaryReached = visitEntry(indexProperties, tupleConsumer, indexKey, entry);
+            for (var entry : comparisonMap.entrySet()) {
+                var boundaryReached = visitEntry(indexProperties, tupleConsumer, indexKey, entry);
                 if (boundaryReached) {
                     return;
                 }
             }
         }
     }
 
-    private boolean visitEntry(ai.timefold.solver.core.impl.score.stream.bavet.common.index.IndexProperties indexProperties,
-            Consumer<T> tupleConsumer,
-            Key_ indexKey, Map.Entry<Key_, ai.timefold.solver.core.impl.score.stream.bavet.common.index.Indexer<T>> entry) {
+    private boolean visitEntry(IndexProperties indexProperties, Consumer<T> tupleConsumer, Key_ indexKey,
+            Map.Entry<Key_, Indexer<T>> entry) {
         // Comparator matches the order of iteration of the map, so the boundary is always found from the bottom up.
-        int comparison = keyComparator.compare(entry.getKey(), indexKey);
+        var comparison = keyComparator.compare(entry.getKey(), indexKey);
         if (comparison >= 0) { // Possibility of reaching the boundary condition.
             if (comparison > 0 || !hasOrEquals) {
                 // Boundary condition reached when we're out of bounds entirely, or when GTE/LTE is not allowed.

core/src/main/java/ai/timefold/solver/core/impl/score/stream/collector/MinMaxUndoableActionable.java

@@ -1,22 +1,21 @@
 package ai.timefold.solver.core.impl.score.stream.collector;
 
 import java.util.Comparator;
-import java.util.LinkedHashMap;
-import java.util.Map;
 import java.util.NavigableMap;
 import java.util.TreeMap;
 import java.util.function.Function;
 
 import ai.timefold.solver.core.impl.util.ConstantLambdaUtils;
 import ai.timefold.solver.core.impl.util.MutableInt;
 
-public final class MinMaxUndoableActionable<Result_, Property_> implements UndoableActionable<Result_, Result_> {
+public final class MinMaxUndoableActionable<Result_, Property_>
+        implements UndoableActionable<Result_, Result_> {
+
     private final boolean isMin;
-    private final NavigableMap<Property_, Map<Result_, MutableInt>> propertyToItemCountMap;
+    private final NavigableMap<Property_, ItemCount<Result_>> propertyToItemCountMap;
     private final Function<? super Result_, ? extends Property_> propertyFunction;
 
-    private MinMaxUndoableActionable(boolean isMin,
-            NavigableMap<Property_, Map<Result_, MutableInt>> propertyToItemCountMap,
+    private MinMaxUndoableActionable(boolean isMin, NavigableMap<Property_, ItemCount<Result_>> propertyToItemCountMap,
             Function<? super Result_, ? extends Property_> propertyFunction) {
         this.isMin = isMin;
         this.propertyToItemCountMap = propertyToItemCountMap;
@@ -40,30 +39,29 @@ public static <Result> MinMaxUndoableActionable<Result, Result> maxCalculator(Co
     }
 
     public static <Result, Property extends Comparable<? super Property>> MinMaxUndoableActionable<Result, Property>
-            minCalculator(
-                    Function<? super Result, ? extends Property> propertyMapper) {
+            minCalculator(Function<? super Result, ? extends Property> propertyMapper) {
         return new MinMaxUndoableActionable<>(true, new TreeMap<>(), propertyMapper);
     }
 
     public static <Result, Property extends Comparable<? super Property>> MinMaxUndoableActionable<Result, Property>
-            maxCalculator(
-                    Function<? super Result, ? extends Property> propertyMapper) {
+            maxCalculator(Function<? super Result, ? extends Property> propertyMapper) {
         return new MinMaxUndoableActionable<>(false, new TreeMap<>(), propertyMapper);
     }
 
     @Override
     public Runnable insert(Result_ item) {
         Property_ key = propertyFunction.apply(item);
-        Map<Result_, MutableInt> itemCountMap = propertyToItemCountMap.computeIfAbsent(key, ignored -> new LinkedHashMap<>());
-        MutableInt count = itemCountMap.computeIfAbsent(item, ignored -> new MutableInt());
+        var value = propertyToItemCountMap.get(key);
+        if (value == null) {
+            value = new ItemCount<>(item, new MutableInt());
+            propertyToItemCountMap.put(key, value);
+        }
+        var count = value.count;
         count.increment();
 
         return () -> {
             if (count.decrement() == 0) {
-                itemCountMap.remove(item);
-                if (itemCountMap.isEmpty()) {
-                    propertyToItemCountMap.remove(key);
-                }
+                propertyToItemCountMap.remove(key);
             }
         };
     }
@@ -73,11 +71,11 @@ public Result_ result() {
         if (propertyToItemCountMap.isEmpty()) {
             return null;
         }
-        return isMin ? getFirstKey(propertyToItemCountMap.firstEntry().getValue())
-                : getFirstKey(propertyToItemCountMap.lastEntry().getValue());
+        var itemCount = isMin ? propertyToItemCountMap.firstEntry().getValue() : propertyToItemCountMap.lastEntry().getValue();
+        return itemCount.item;
     }
 
-    private static <Key_> Key_ getFirstKey(Map<Key_, ?> map) {
-        return map.keySet().iterator().next();
+    private record ItemCount<Item_>(Item_ item, MutableInt count) {
     }
+
 }