8371164: ArrayList.addAll() optimizations

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2025, 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
@@ -750,9 +750,17 @@ public void clear() {
      * @throws NullPointerException if the specified collection is null
      */
     public boolean addAll(Collection<? extends E> c) {
-        Object[] a = c.toArray();
+        Object[] a;
+        int numNew;
+        if (c.getClass() == ArrayList.class) {
+            ArrayList<?> src = (ArrayList<?>) c;
+            a = src.elementData;
+            numNew = src.size;
+        } else {
+            a = c.toArray();
+            numNew = a.length;
+        }
         modCount++;
-        int numNew = a.length;
         if (numNew == 0)
             return false;
         Object[] elementData;

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

@@ -5253,6 +5253,20 @@ public boolean removeIf(Predicate<? super E> filter) {
         public int hashCode() {
             return Objects.hashCode(element);
         }
+        @Override
+        public Object[] toArray() {
+            return new Object[] {element};
+        }
+        @Override
+        @SuppressWarnings("unchecked")
+        public <T> T[] toArray(T[] a) {
+            if (a.length < 1)
+                a = (T[])java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), 1);
+            a[0] = (T)element;
+            if (a.length > 1)
+                a[1] = null;
+            return a;
+        }
     }
 
     /**

test/jdk/java/util/Collection/MOAT.java

@@ -887,6 +887,28 @@ private static void testStringElement(Collection<Integer> c) {
         catch (Throwable t) { unexpected(t); }
     }
 
+    private static void testAddAll(Collection<Integer> c) {
+        clear(c);
+
+        // Test ArrayList source
+        ArrayList<Integer> arrayListSource = new ArrayList<>();
+        arrayListSource.add(42);
+        arrayListSource.add(99);
+        check(c.addAll(arrayListSource));
+        equal(c.size(), arrayListSource.size());
+        check(c.containsAll(arrayListSource));
+
+        clear(c);
+
+        // Test non-ArrayList source
+        LinkedList<Integer> linkedListSource = new LinkedList<>();
+        linkedListSource.add(77);
+        linkedListSource.add(88);
+        check(c.addAll(linkedListSource));
+        equal(c.size(), linkedListSource.size());
+        check(c.containsAll(linkedListSource));
+    }
+
     private static void testConcurrentCollection(Collection<Integer> c) {
         try {
             c.add(1);
@@ -1294,6 +1316,8 @@ private static void testCollection1(Collection<Integer> c) {
         clear(c);      testStringElement(c);
         oneElement(c); testStringElement(c);
 
+        testAddAll(c);
+
         if (c.getClass().getName().matches(".*concurrent.*"))
             testConcurrentCollection(c);
 

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

@@ -0,0 +1,128 @@
+/*
+ * Copyright Amazon.com Inc. 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 java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.WeakHashMap;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+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;
+
+
+/**
+ * Benchmark measuring ArrayList addAll() performance.
+ *
+ * Tests the performance of ArrayList.addAll() when copying from another ArrayList.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+@Warmup(iterations = 3, time = 1, timeUnit = TimeUnit.SECONDS)
+@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@Fork(value = 1, jvmArgs = { "-XX:+UseParallelGC", "-Xmx3g" })
+public class ArrayListBulkOpsBenchmark {
+    @Param({"0", "1", "5", "75"})
+    int size;
+
+    @Param({"ArrayList", "LinkedList"})
+    String type;
+
+    List<String> source;
+
+    @Setup(Level.Trial)
+    public void setup() {
+        switch (type) {
+            case "ArrayList" -> source = new ArrayList<>(size);
+            case "LinkedList" -> source = new LinkedList<>();
+        }
+        for (int i = 0; i < size; i++) source.add("key" + i);
+    }
+
+    @Benchmark
+    public ArrayList<String> addAll() {
+        ArrayList<String> result = new ArrayList<>(size);
+        result.addAll(source);
+        return result;
+    }
+
+    static void poisonCallSites() {
+        HashMap<String, String> hashMapSource = new HashMap<>();
+        TreeSet<String> treeSetSource = new TreeSet<>();
+        WeakHashMap<String, String> weakHashMapSource = new WeakHashMap<>();
+        for (int i = 0; i < 75; i++) {
+            hashMapSource.put("key" + i, "value" + i);
+            treeSetSource.add("key" + i);
+            weakHashMapSource.put("key" + i, "value" + i);
+        }
+        // Poison ArrayList.addAll() with different Collection types
+        for (int i = 0; i < 40_000; i++) {
+            ArrayList<Object> temp = new ArrayList<>();
+            temp.addAll(hashMapSource.entrySet());
+            temp.addAll(treeSetSource);
+            temp.addAll(weakHashMapSource.keySet());
+        }
+    }
+
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    @State(Scope.Benchmark)
+    @Warmup(iterations = 3, time = 1, timeUnit = TimeUnit.SECONDS)
+    @Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+    @Fork(value = 1, jvmArgs = { "-XX:+UseParallelGC", "-Xmx3g" })
+    public static class SingletonSet {
+        Set<String> singletonSetSource = Collections.singleton("key");
+
+        @Param({ "false", "true" })
+        private boolean poison;
+
+        @Setup(Level.Trial)
+        public void setup() {
+            if (poison) poisonCallSites();
+        }
+
+        @Benchmark
+        public ArrayList<String> addAllSingletonSet() {
+            ArrayList<String> result = new ArrayList<>(1);
+            result.addAll(singletonSetSource);
+            return result;
+        }
+    }
+}