8225339: Optimize HashMap.keySet()/HashMap.values()/HashSet toArray() methods

Reviewed-by: rriggs, redestad, smarks

src/java.base/share/classes/java/util/HashMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -911,6 +911,74 @@ public class HashMap<K,V> extends AbstractMap<K,V>
         return ks;
     }
 
+    /**
+     * Prepares the array for {@link Collection#toArray(Object[])} implementation.
+     * If supplied array is smaller than this map size, a new array is allocated.
+     * If supplied array is bigger than this map size, a null is written at size index.
+     *
+     * @param a an original array passed to {@code toArray()} method
+     * @param <T> type of array elements
+     * @return an array ready to be filled and returned from {@code toArray()} method.
+     */
+    @SuppressWarnings("unchecked")
+    final <T> T[] prepareArray(T[] a) {
+        int size = this.size;
+        if (a.length < size) {
+            return (T[]) java.lang.reflect.Array
+                    .newInstance(a.getClass().getComponentType(), size);
+        }
+        if (a.length > size) {
+            a[size] = null;
+        }
+        return a;
+    }
+
+    /**
+     * Fills an array with this map keys and returns it. This method assumes
+     * that input array is big enough to fit all the keys. Use
+     * {@link #prepareArray(Object[])} to ensure this.
+     *
+     * @param a an array to fill
+     * @param <T> type of array elements
+     * @return supplied array
+     */
+    <T> T[] keysToArray(T[] a) {
+        Object[] r = a;
+        Node<K,V>[] tab;
+        int idx = 0;
+        if (size > 0 && (tab = table) != null) {
+            for (Node<K,V> e : tab) {
+                for (; e != null; e = e.next) {
+                    r[idx++] = e.key;
+                }
+            }
+        }
+        return a;
+    }
+
+    /**
+     * Fills an array with this map values and returns it. This method assumes
+     * that input array is big enough to fit all the values. Use
+     * {@link #prepareArray(Object[])} to ensure this.
+     *
+     * @param a an array to fill
+     * @param <T> type of array elements
+     * @return supplied array
+     */
+    <T> T[] valuesToArray(T[] a) {
+        Object[] r = a;
+        Node<K,V>[] tab;
+        int idx = 0;
+        if (size > 0 && (tab = table) != null) {
+            for (Node<K,V> e : tab) {
+                for (; e != null; e = e.next) {
+                    r[idx++] = e.value;
+                }
+            }
+        }
+        return a;
+    }
+
     final class KeySet extends AbstractSet<K> {
         public final int size()                 { return size; }
         public final void clear()               { HashMap.this.clear(); }
@@ -922,6 +990,15 @@ public class HashMap<K,V> extends AbstractMap<K,V>
         public final Spliterator<K> spliterator() {
             return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
         }
+
+        public Object[] toArray() {
+            return keysToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return keysToArray(prepareArray(a));
+        }
+
         public final void forEach(Consumer<? super K> action) {
             Node<K,V>[] tab;
             if (action == null)
@@ -970,6 +1047,15 @@ public class HashMap<K,V> extends AbstractMap<K,V>
         public final Spliterator<V> spliterator() {
             return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
         }
+
+        public Object[] toArray() {
+            return valuesToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return valuesToArray(prepareArray(a));
+        }
+
         public final void forEach(Consumer<? super V> action) {
             Node<K,V>[] tab;
             if (action == null)

src/java.base/share/classes/java/util/HashSet.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -358,4 +358,14 @@ public class HashSet<E>
     public Spliterator<E> spliterator() {
         return new HashMap.KeySpliterator<>(map, 0, -1, 0, 0);
     }
+
+    @Override
+    public Object[] toArray() {
+        return map.keysToArray(new Object[map.size()]);
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+        return map.keysToArray(map.prepareArray(a));
+    }
 }

src/java.base/share/classes/java/util/LinkedHashMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -536,6 +536,26 @@ public class LinkedHashMap<K,V>
         return ks;
     }
 
+    @Override
+    final <T> T[] keysToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            r[idx++] = e.key;
+        }
+        return a;
+    }
+
+    @Override
+    final <T> T[] valuesToArray(T[] a) {
+        Object[] r = a;
+        int idx = 0;
+        for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
+            r[idx++] = e.value;
+        }
+        return a;
+    }
+
     final class LinkedKeySet extends AbstractSet<K> {
         public final int size()                 { return size; }
         public final void clear()               { LinkedHashMap.this.clear(); }
@@ -551,6 +571,15 @@ public class LinkedHashMap<K,V>
                                             Spliterator.ORDERED |
                                             Spliterator.DISTINCT);
         }
+
+        public Object[] toArray() {
+            return keysToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return keysToArray(prepareArray(a));
+        }
+
         public final void forEach(Consumer<? super K> action) {
             if (action == null)
                 throw new NullPointerException();
@@ -600,6 +629,15 @@ public class LinkedHashMap<K,V>
             return Spliterators.spliterator(this, Spliterator.SIZED |
                                             Spliterator.ORDERED);
         }
+
+        public Object[] toArray() {
+            return valuesToArray(new Object[size]);
+        }
+
+        public <T> T[] toArray(T[] a) {
+            return valuesToArray(prepareArray(a));
+        }
+
         public final void forEach(Consumer<? super V> action) {
             if (action == null)
                 throw new NullPointerException();

test/jdk/java/util/HashMap/ToArray.java

@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.LongStream;
+
+/*
+ * @test
+ * @summary HashMap.toArray() behavior tests
+ * @author tvaleev
+ */
+public class ToArray {
+    public static void main(String[] args) {
+        checkMap(false);
+        checkMap(true);
+        checkSet(false);
+        checkSet(true);
+    }
+
+    private static <T extends Comparable<T>> void checkToArray(String message, T[] expected, Collection<T> collection,
+                                                               boolean ignoreOrder) {
+        if (ignoreOrder) {
+            Arrays.sort(expected);
+        }
+        checkToObjectArray(message, expected, collection, ignoreOrder);
+        checkToTypedArray(message, expected, Arrays.copyOf(expected, 0), collection, ignoreOrder);
+        checkToTypedArray(message, expected, expected.clone(), collection, ignoreOrder);
+        if (expected.length > 0) {
+            T[] biggerArray = Arrays.copyOf(expected, expected.length * 2);
+            System.arraycopy(expected, 0, biggerArray, expected.length, expected.length);
+            checkToTypedArray(message, expected, biggerArray, collection, ignoreOrder);
+        }
+    }
+
+    private static <T extends Comparable<T>> void checkToTypedArray(String message, T[] expected, T[] inputArray,
+                                                                    Collection<T> collection, boolean ignoreOrder) {
+        T[] res = collection.toArray(inputArray);
+        if (expected.length <= inputArray.length && res != inputArray) {
+            throw new AssertionError(message + ": not the same array returned");
+        }
+        if (res.getClass() != expected.getClass()) {
+            throw new AssertionError(message + ": wrong class returned: " + res.getClass());
+        }
+        if (res.length < expected.length) {
+            throw new AssertionError(message + ": length is smaller than expected: " + res.length + " < " + expected.length);
+        }
+        if (ignoreOrder) {
+            Arrays.sort(res, 0, Math.min(res.length, expected.length));
+        }
+        if (inputArray.length <= expected.length) {
+            if (!Arrays.equals(res, expected)) {
+                throw new AssertionError(message + ": not equal: " + Arrays.toString(expected) + " != " +
+                        Arrays.toString(res));
+            }
+        } else {
+            int mismatch = Arrays.mismatch(expected, res);
+            if (mismatch != expected.length) {
+                throw new AssertionError(message + ": mismatch at " + mismatch);
+            }
+            if (res[expected.length] != null) {
+                throw new AssertionError(message + ": no null at position " + expected.length);
+            }
+            // The tail of bigger array after expected.length position must be untouched
+            mismatch = Arrays
+                    .mismatch(expected, 1, expected.length, res, expected.length + 1, res.length);
+            if (mismatch != -1) {
+                throw new AssertionError(message + ": mismatch at " + mismatch);
+            }
+        }
+    }
+
+    private static <T extends Comparable<T>> void checkToObjectArray(String message, T[] expected,
+                                                                     Collection<T> collection, boolean ignoreOrder) {
+        Object[] objects = collection.toArray();
+        if (objects.getClass() != Object[].class) {
+            throw new AssertionError(message + ": wrong class returned: " + objects.getClass());
+        }
+        if (ignoreOrder) {
+            Arrays.sort(objects);
+        }
+        int mismatch = Arrays.mismatch(expected, objects);
+        if (mismatch != -1) {
+            throw new AssertionError(message + ": mismatch at " + mismatch);
+        }
+    }
+
+    private static void checkMap(boolean ordered) {
+        Map<String, String> map = ordered ? new LinkedHashMap<>() : new HashMap<>();
+        checkToArray("Empty-keys", new String[0], map.keySet(), !ordered);
+        checkToArray("Empty-values", new String[0], map.values(), !ordered);
+
+        List<String> keys = new ArrayList<>();
+        List<String> values = new ArrayList<>();
+        for (int i = 0; i < 100; i++) {
+            keys.add(String.valueOf(i));
+            values.add(String.valueOf(i * 2));
+            map.put(String.valueOf(i), String.valueOf(i * 2));
+            checkToArray(i + "-keys", keys.toArray(new String[0]), map.keySet(), !ordered);
+            checkToArray(i + "-values", values.toArray(new String[0]), map.values(), !ordered);
+        }
+        map.clear();
+        checkToArray("Empty-keys", new String[0], map.keySet(), !ordered);
+        checkToArray("Empty-values", new String[0], map.values(), !ordered);
+    }
+
+    private static void checkSet(boolean ordered) {
+        Collection<String> set = ordered ? new LinkedHashSet<>() : new HashSet<>();
+        checkToArray("Empty", new String[0], set, !ordered);
+        set.add("foo");
+        checkToArray("One", new String[]{"foo"}, set, !ordered);
+        set.add("bar");
+        checkToArray("Two", new String[]{"foo", "bar"}, set, !ordered);
+
+        Collection<Long> longSet = ordered ? new LinkedHashSet<>() : new HashSet<>();
+        for (int x = 0; x < 100; x++) {
+            longSet.add((long) x);
+        }
+        checkToArray("100", LongStream.range(0, 100).boxed().toArray(Long[]::new), longSet, !ordered);
+        longSet.clear();
+        checkToArray("After clear", new Long[0], longSet, !ordered);
+        for (int x = 0; x < 100; x++) {
+            longSet.add(((long) x) | (((long) x) << 32));
+        }
+        checkToArray("Collisions", LongStream.range(0, 100).mapToObj(x -> x | (x << 32))
+                .toArray(Long[]::new), longSet, !ordered);
+    }
+}

test/micro/org/openjdk/bench/java/util/HashMapToArray.java

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.java.util;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@Fork(3)
+@State(Scope.Thread)
+public class HashMapToArray {
+
+    @Param({"0", "1", "10", "1000", "100000"})
+    public int size;
+
+    @Param({"HashMap", "LinkedHashMap"})
+    public String mapType;
+
+    private Map<Integer, Integer> map;
+
+    @Setup
+    public void setup() {
+        switch (mapType) {
+            case "HashMap":
+                map = new HashMap<>();
+                break;
+            case "LinkedHashMap":
+                map = new LinkedHashMap<>();
+                break;
+            default:
+                throw new IllegalStateException();
+        }
+        for (int i = 0; i < size; i++) {
+            map.put(i, i * i);
+        }
+    }
+
+    @Benchmark
+    public Object[] testKeySetToArray() {
+        return map.keySet().toArray();
+    }
+
+    @Benchmark
+    public Object[] testKeySetToArrayTyped() {
+        return map.keySet().toArray(new Integer[0]);
+    }
+
+    @Benchmark
+    public Object[] testValuesToArray() {
+        return map.values().toArray();
+    }
+
+    @Benchmark
+    public Object[] testValuesToArrayTyped() {
+        return map.values().toArray(new Integer[0]);
+    }
+}