8365058: Enhance CopyOnWriteArraySet

Reviewed-by: rhalade, skoivu, vklang, rriggs

src/java.base/share/classes/java/util/concurrent/CopyOnWriteArraySet.java

@@ -35,6 +35,13 @@
 
 package java.util.concurrent;
 
+import jdk.internal.misc.Unsafe;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectStreamException;
+import java.io.Serial;
+import java.io.StreamCorruptedException;
 import java.util.AbstractSet;
 import java.util.Collection;
 import java.util.Iterator;
@@ -445,4 +452,38 @@ public class CopyOnWriteArraySet<E> extends AbstractSet<E>
         return Spliterators.spliterator
             (al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT);
     }
+
+    /**
+     * De-serialization without data not supported for this class.
+     */
+    @Serial
+    private void readObjectNoData() throws ObjectStreamException {
+        throw new StreamCorruptedException("Deserialized CopyOnWriteArraySet requires data");
+    }
+
+    /**
+     * Reconstitutes the {@code CopyOnWriteArraySet} instance from a stream
+     * (that is, deserializes it).
+     * @throws StreamCorruptedException if the object read from the stream is invalid.
+     */
+    @Serial
+    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
+        CopyOnWriteArrayList<E> newAl; // Set during the duplicate check
+
+        @SuppressWarnings("unchecked")
+        CopyOnWriteArrayList<E> inAl = (CopyOnWriteArrayList<E>) in.readFields().get("al", null);
+
+        if (inAl == null
+                || inAl.getClass() != CopyOnWriteArrayList.class
+                || (newAl = new CopyOnWriteArrayList<>()).addAllAbsent(inAl) != inAl.size()) {
+            throw new StreamCorruptedException("Content is invalid");
+        }
+
+        final Unsafe U = Unsafe.getUnsafe();
+        U.putReference(
+                this,
+                U.objectFieldOffset(CopyOnWriteArraySet.class, "al"),
+                newAl
+        );
+    }
 }

test/jdk/java/util/concurrent/CopyOnWriteArraySet/SerializationTest.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 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
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8365058
+ * @summary Check basic correctness of de-serialization
+ * @run junit SerializationTest
+ */
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class SerializationTest {
+
+    // Ensure basic serialization round trip correctness
+    @ParameterizedTest
+    @MethodSource
+    void roundTripTest(CopyOnWriteArraySet<?> expected) {
+        var bytes = ser(expected);
+        var actual = deSer(bytes);
+        assertEquals(CopyOnWriteArraySet.class, actual.getClass());
+        assertEquals(expected, actual);
+    }
+
+    private static Stream<CopyOnWriteArraySet<?>> roundTripTest() {
+        return Stream.of(
+                new CopyOnWriteArraySet<>(),
+                new CopyOnWriteArraySet<>(List.of(1, 2, 3)),
+                new CopyOnWriteArraySet<>(Set.of("Foo", "Bar", "Baz"))
+        );
+    }
+
+    private static byte[] ser(Object obj) {
+        return assertDoesNotThrow(() -> {
+            try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+                 ObjectOutputStream oos = new ObjectOutputStream(byteArrayOutputStream)) {
+                oos.writeObject(obj);
+                return byteArrayOutputStream.toByteArray();
+            }
+        }, "Unexpected error during serialization");
+    }
+
+    private static Object deSer(byte[] bytes) {
+        return assertDoesNotThrow(() -> {
+            try (ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(bytes);
+                 ObjectInputStream ois = new ObjectInputStream(byteArrayInputStream)) {
+                return ois.readObject();
+            }
+        }, "Unexpected error during de-serialization");
+    }
+}