8310913: Move ReferencedKeyMap to jdk.internal so it may be shared

Reviewed-by: naoto, rriggs, mchung, liach

src/java.base/share/classes/java/lang/invoke/MethodType.java

@@ -33,7 +33,9 @@ import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.function.Supplier;
 import java.util.List;
+import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.Optional;
@@ -42,7 +44,8 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.stream.Stream;
 
-import jdk.internal.access.SharedSecrets;
+import jdk.internal.util.ReferencedKeySet;
+import jdk.internal.util.ReferenceKey;
 import jdk.internal.vm.annotation.Stable;
 import sun.invoke.util.BytecodeDescriptor;
 import sun.invoke.util.VerifyType;
@@ -227,7 +230,13 @@ class MethodType
         return new IndexOutOfBoundsException(num.toString());
     }
 
-    static final ConcurrentWeakInternSet<MethodType> internTable = new ConcurrentWeakInternSet<>();
+    static final ReferencedKeySet<MethodType> internTable =
+        ReferencedKeySet.create(false, true, new Supplier<>() {
+            @Override
+            public Map<ReferenceKey<MethodType>, ReferenceKey<MethodType>> get() {
+                return new ConcurrentHashMap<>(512);
+            }
+        });
 
     static final Class<?>[] NO_PTYPES = {};
 
@@ -405,7 +414,7 @@ class MethodType
             mt = new MethodType(rtype, ptypes);
         }
         mt.form = MethodTypeForm.findForm(mt);
-        return internTable.add(mt);
+        return internTable.intern(mt);
     }
     private static final @Stable MethodType[] objectOnlyTypes = new MethodType[20];
 
@@ -883,10 +892,6 @@ class MethodType
      * @param x object to compare
      * @see Object#equals(Object)
      */
-    // This implementation may also return true if x is a WeakEntry containing
-    // a method type that is equal to this. This is an internal implementation
-    // detail to allow for faster method type lookups.
-    // See ConcurrentWeakInternSet.WeakEntry#equals(Object)
     @Override
     public boolean equals(Object x) {
         if (this == x) {
@@ -895,10 +900,6 @@ class MethodType
         if (x instanceof MethodType mt) {
             return equals(mt);
         }
-        if (x instanceof ConcurrentWeakInternSet.WeakEntry<?> e
-                && e.get() instanceof MethodType mt) {
-            return equals(mt);
-        }
         return false;
     }
 
@@ -1390,112 +1391,4 @@ s.writeObject(this.parameterArray());
         wrapAlt = null;
         return mt;
     }
-
-    /**
-     * Simple implementation of weak concurrent intern set.
-     *
-     * @param <T> interned type
-     */
-    private static class ConcurrentWeakInternSet<T> {
-
-        private final ConcurrentMap<WeakEntry<T>, WeakEntry<T>> map;
-        private final ReferenceQueue<T> stale;
-
-        public ConcurrentWeakInternSet() {
-            this.map = new ConcurrentHashMap<>(512);
-            this.stale = SharedSecrets.getJavaLangRefAccess().newNativeReferenceQueue();
-        }
-
-        /**
-         * Get the existing interned element.
-         * This method returns null if no element is interned.
-         *
-         * @param elem element to look up
-         * @return the interned element
-         */
-        public T get(T elem) {
-            if (elem == null) throw new NullPointerException();
-            expungeStaleElements();
-
-            WeakEntry<T> value = map.get(elem);
-            if (value != null) {
-                T res = value.get();
-                if (res != null) {
-                    return res;
-                }
-            }
-            return null;
-        }
-
-        /**
-         * Interns the element.
-         * Always returns non-null element, matching the one in the intern set.
-         * Under the race against another add(), it can return <i>different</i>
-         * element, if another thread beats us to interning it.
-         *
-         * @param elem element to add
-         * @return element that was actually added
-         */
-        public T add(T elem) {
-            if (elem == null) throw new NullPointerException();
-
-            // Playing double race here, and so spinloop is required.
-            // First race is with two concurrent updaters.
-            // Second race is with GC purging weak ref under our feet.
-            // Hopefully, we almost always end up with a single pass.
-            T interned;
-            WeakEntry<T> e = new WeakEntry<>(elem, stale);
-            do {
-                expungeStaleElements();
-                WeakEntry<T> exist = map.putIfAbsent(e, e);
-                interned = (exist == null) ? elem : exist.get();
-            } while (interned == null);
-            return interned;
-        }
-
-        private void expungeStaleElements() {
-            Reference<? extends T> reference;
-            while ((reference = stale.poll()) != null) {
-                map.remove(reference);
-            }
-        }
-
-        private static class WeakEntry<T> extends WeakReference<T> {
-
-            public final int hashcode;
-
-            public WeakEntry(T key, ReferenceQueue<T> queue) {
-                super(key, queue);
-                hashcode = key.hashCode();
-            }
-
-            /**
-             * This implementation returns {@code true} if {@code obj} is another
-             * {@code WeakEntry} whose referent is equal to this referent, or
-             * if {@code obj} is equal to the referent of this. This allows
-             * lookups to be made without wrapping in a {@code WeakEntry}.
-             *
-             * @param obj the object to compare
-             * @return true if {@code obj} is equal to this or the referent of this
-             * @see MethodType#equals(Object)
-             * @see Object#equals(Object)
-             */
-            @Override
-            public boolean equals(Object obj) {
-                Object mine = get();
-                if (obj instanceof WeakEntry<?> we) {
-                    Object that = we.get();
-                    return (that == null || mine == null) ? (this == obj) : mine.equals(that);
-                }
-                return (mine == null) ? (obj == null) : mine.equals(obj);
-            }
-
-            @Override
-            public int hashCode() {
-                return hashcode;
-            }
-
-        }
-    }
-
 }

src/java.base/share/classes/java/lang/runtime/Carriers.java

@@ -35,6 +35,7 @@ import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 
 import jdk.internal.misc.Unsafe;
+import jdk.internal.util.ReferencedKeyMap;
 
 import static java.lang.invoke.MethodType.methodType;
 
@@ -366,7 +367,7 @@ final class Carriers {
          * Cache mapping {@link MethodType} to previously defined {@link CarrierElements}.
          */
         private static final Map<MethodType, CarrierElements>
-                methodTypeCache = ReferencedKeyMap.create(ConcurrentHashMap::new);
+                methodTypeCache = ReferencedKeyMap.create(false, ConcurrentHashMap::new);
 
         /**
          * Permute a raw constructor and component accessor {@link MethodHandle MethodHandles} to

src/java.base/share/classes/jdk/internal/access/JavaLangRefAccess.java

@@ -54,7 +54,7 @@ public interface JavaLangRefAccess {
     /**
      * Constructs a new NativeReferenceQueue.
      *
-     * Invoked by MethodType.ConcurrentWeakInternSet
+     * Invoked by jdk.internal.util.ReferencedKeyMap
      */
     <T> ReferenceQueue<T> newNativeReferenceQueue();
 }

src/java.base/share/classes/jdk/internal/util/ReferenceKey.java

@@ -23,12 +23,9 @@
  * questions.
  */
 
-package java.lang.runtime;
+package jdk.internal.util;
 
-import java.lang.ref.ReferenceQueue;
+import java.lang.ref.Reference;
-import java.lang.ref.SoftReference;
-import java.lang.ref.WeakReference;
-import java.util.Objects;
 
 /**
  * View/wrapper of keys used by the backing {@link ReferencedKeyMap}.
@@ -39,11 +36,8 @@ import java.util.Objects;
  * @param <T> key type
  *
  * @since 21
- *
- * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
- *          Do not rely on its availability.
  */
-sealed interface ReferenceKey<T> permits StrongReferenceKey, WeakReferenceKey, SoftReferenceKey {
+public sealed interface ReferenceKey<T> permits StrongReferenceKey, WeakReferenceKey, SoftReferenceKey {
     /**
      * {@return the value of the unwrapped key}
      */

src/java.base/share/classes/jdk/internal/util/ReferencedKeyMap.java

@@ -23,7 +23,7 @@
  * questions.
  */
 
-package java.lang.runtime;
+package jdk.internal.util;
 
 import java.lang.ref.Reference;
 import java.lang.ref.ReferenceQueue;
@@ -37,9 +37,12 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import jdk.internal.access.SharedSecrets;
+
 /**
  * This class provides management of {@link Map maps} where it is desirable to
  * remove entries automatically when the key is garbage collected. This is
@@ -78,11 +81,8 @@ import java.util.stream.Stream;
  * @param <V> the type of mapped values
  *
  * @since 21
- *
- * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
- *          Do not rely on its availability.
  */
-final class ReferencedKeyMap<K, V> implements Map<K, V> {
+public final class ReferencedKeyMap<K, V> implements Map<K, V> {
     /**
      * true if {@link SoftReference} keys are to be used,
      * {@link WeakReference} otherwise.
@@ -95,7 +95,7 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
     private final Map<ReferenceKey<K>, V> map;
 
     /**
-     * {@link ReferenceQueue} for cleaning up {@link WeakReferenceKey EntryKeys}.
+     * {@link ReferenceQueue} for cleaning up entries.
      */
     private final ReferenceQueue<K> stale;
 
@@ -105,11 +105,12 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
      * @param isSoft          true if {@link SoftReference} keys are to
      *                        be used, {@link WeakReference} otherwise.
      * @param map             backing map
+     * @param stale           {@link ReferenceQueue} for cleaning up entries
      */
-    private ReferencedKeyMap(boolean isSoft, Map<ReferenceKey<K>, V> map) {
+    private ReferencedKeyMap(boolean isSoft, Map<ReferenceKey<K>, V> map, ReferenceQueue<K> stale) {
         this.isSoft = isSoft;
         this.map = map;
-        this.stale = new ReferenceQueue<>();
+        this.stale = stale;
     }
 
     /**
@@ -124,15 +125,18 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
      * @param <K> the type of keys maintained by the new map
      * @param <V> the type of mapped values
      */
-    static <K, V> ReferencedKeyMap<K, V>
+    public static <K, V> ReferencedKeyMap<K, V>
     create(boolean isSoft, Supplier<Map<ReferenceKey<K>, V>> supplier) {
-        return new ReferencedKeyMap<K, V>(isSoft, supplier.get());
+        return create(isSoft, false, supplier);
     }
 
     /**
-     * Create a new {@link ReferencedKeyMap} map using
+     * Create a new {@link ReferencedKeyMap} map.
-     * {@link WeakReference} keys.
      *
+     * @param isSoft          true if {@link SoftReference} keys are to
+     *                        be used, {@link WeakReference} otherwise.
+     * @param useNativeQueue  true if uses NativeReferenceQueue
+     *                        otherwise use {@link ReferenceQueue}.
      * @param supplier        {@link Supplier} of the backing map
      *
      * @return a new map with {@link Reference} keys
@@ -140,9 +144,12 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
      * @param <K> the type of keys maintained by the new map
      * @param <V> the type of mapped values
      */
-    static <K, V> ReferencedKeyMap<K, V>
+    public static <K, V> ReferencedKeyMap<K, V>
-    create(Supplier<Map<ReferenceKey<K>, V>> supplier) {
+    create(boolean isSoft, boolean useNativeQueue, Supplier<Map<ReferenceKey<K>, V>> supplier) {
-        return new ReferencedKeyMap<K, V>(false, supplier.get());
+        return new ReferencedKeyMap<K, V>(isSoft, supplier.get(),
+                useNativeQueue ? SharedSecrets.getJavaLangRefAccess().newNativeReferenceQueue()
+                               : new ReferenceQueue<>()
+                );
     }
 
     /**
@@ -320,10 +327,9 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
     /**
      * Removes enqueued weak references from map.
      */
-    @SuppressWarnings("unchecked")
     public void removeStaleReferences() {
         while (true) {
-            WeakReferenceKey<K> key = (WeakReferenceKey<K>)stale.poll();
+            Object key = stale.poll();
             if (key == null) {
                 break;
             }
@@ -331,4 +337,106 @@ final class ReferencedKeyMap<K, V> implements Map<K, V> {
         }
     }
 
+    /**
+     * Puts an entry where the key and the value are the same. Used for
+     * interning values in a set.
+     *
+     * @implNote Requires a {@link ReferencedKeyMap} whose {@code V} type
+     * is a {@code ReferenceKey<K>}. Otherwise, a {@link ClassCastException} will
+     * be thrown.
+     *
+     * @param setMap    {@link ReferencedKeyMap} where interning takes place
+     * @param key       key to add
+     *
+     * @param <T> type of key
+     *
+     * @return the old key instance if found otherwise the new key instance
+     *
+     * @throws ClassCastException if {@code V} is not {@code EntryKey<T>}
+     */
+    static <T> T intern(ReferencedKeyMap<T, ReferenceKey<T>> setMap, T key) {
+        T value = existingKey(setMap, key);
+        if (value != null) {
+            return value;
+        }
+        return internKey(setMap, key);
+    }
+
+    /**
+     * Puts an entry where the key and the value are the same. Used for
+     * interning values in a set.
+     *
+     * @implNote Requires a {@link ReferencedKeyMap} whose {@code V} type
+     * is a {@code ReferenceKey<K>}. Otherwise, a {@link ClassCastException} will
+     * be thrown.
+     *
+     * @param setMap    {@link ReferencedKeyMap} where interning takes place
+     * @param key       key to add
+     * @param interner  operation to apply to key before adding to map
+     *
+     * @param <T> type of key
+     *
+     * @return the old key instance if found otherwise the new key instance
+     *
+     * @throws ClassCastException if {@code V} is not {@code EntryKey<T>}
+     *
+     * @implNote This version of intern should not be called during phase1
+     * using a lambda. Use an UnaryOperator instance instead.
+     */
+    static <T> T intern(ReferencedKeyMap<T, ReferenceKey<T>> setMap, T key, UnaryOperator<T> interner) {
+        T value = existingKey(setMap, key);
+        if (value != null) {
+            return value;
+        }
+        key = interner.apply(key);
+        return internKey(setMap, key);
+    }
+
+    /**
+     * Check if the key already exists in the map.
+     *
+     * @param setMap    {@link ReferencedKeyMap} where interning takes place
+     * @param key       key to test
+     *
+     * @param <T> type of key
+     *
+     * @return key if found otherwise null
+     */
+    private static <T> T existingKey(ReferencedKeyMap<T, ReferenceKey<T>> setMap, T key) {
+        setMap.removeStaleReferences();
+        ReferenceKey<T> entryKey = setMap.get(setMap.lookupKey(key));
+        return entryKey != null ? entryKey.get() : null;
+    }
+
+    /**
+     * Attempt to add key to map.
+     *
+     * @param setMap    {@link ReferencedKeyMap} where interning takes place
+     * @param key       key to add
+     *
+     * @param <T> type of key
+     *
+     * @return the old key instance if found otherwise the new key instance
+     */
+    private static <T> T internKey(ReferencedKeyMap<T, ReferenceKey<T>> setMap, T key) {
+        ReferenceKey<T> entryKey = setMap.entryKey(key);
+        T interned;
+        do {
+            setMap.removeStaleReferences();
+            ReferenceKey<T> existing = setMap.map.putIfAbsent(entryKey, entryKey);
+            if (existing == null) {
+                return key;
+            } else {
+                // If {@code putIfAbsent} returns non-null then was actually a
+                // {@code replace} and older key was used. In that case the new
+                // key was not used and the reference marked stale.
+                interned = existing.get();
+                if (interned != null) {
+                    entryKey.unused();
+                }
+            }
+        } while (interned == null);
+        return interned;
+    }
+
 }

src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java

@@ -0,0 +1,205 @@
+/*
+ * Copyright (c) 2023, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 jdk.internal.util;
+
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
+
+/**
+ * This class provides management of {@link Set set} where it is desirable to
+ * remove elements automatically when the element is garbage collected. This is
+ * accomplished by using a backing map where the keys and values are either a
+ * {@link WeakReference} or a {@link SoftReference}.
+ * <p>
+ * To create a {@link ReferencedKeySet} the user must provide a {@link Supplier}
+ * of the backing map and whether {@link WeakReference} or
+ * {@link SoftReference} is to be used.
+ * {@snippet :
+ * Set<Long> set;
+ *
+ * set = ReferencedKeySet.create(false, HashMap::new);
+ * set.add(30_000_000L);
+ * set.add(30_000_001L);
+ * set.add(30_000_002L);
+ * set.add(30_000_003L);
+ * set.add(30_000_004L);
+ *
+ * set = ReferencedKeySet.create(true, ConcurrentHashMap::new);
+ * set.add(40_000_000L);
+ * set.add(40_000_001L);
+ * set.add(40_000_002L);
+ * set.add(40_000_003L);
+ * set.add(40_000_004L);
+ * }
+ *
+ * @implNote Care must be given that the backing map does replacement by
+ * replacing the value in the map entry instead of deleting the old entry and
+ * adding a new entry, otherwise replaced entries may end up with a strongly
+ * referenced key. {@link HashMap} and {@link ConcurrentHashMap} are known
+ * to be safe.
+ *
+ * @param <T> the type of elements maintained by this set
+ */
+public final class ReferencedKeySet<T> extends AbstractSet<T> {
+    /**
+     * Backing {@link ReferencedKeySet} map.
+     */
+    final ReferencedKeyMap<T, ReferenceKey<T>> map;
+
+    /**
+     * Private constructor.
+     *
+     * @param map     backing map
+     */
+    private ReferencedKeySet(ReferencedKeyMap<T, ReferenceKey<T>> map) {
+        this.map = map;
+    }
+
+    /**
+     * Create a new {@link ReferencedKeySet} elements.
+     *
+     * @param isSoft          true if {@link SoftReference} elements are to
+     *                        be used, {@link WeakReference} otherwise.
+     * @param supplier        {@link Supplier} of the backing map
+     *
+     * @return a new set with {@link Reference} elements
+     *
+     * @param <E> the type of elements maintained by this set
+     */
+    public static <E> ReferencedKeySet<E>
+    create(boolean isSoft, Supplier<Map<ReferenceKey<E>, ReferenceKey<E>>> supplier) {
+        return create(isSoft, false, supplier);
+    }
+
+    /**
+     * Create a new {@link ReferencedKeySet} elements.
+     *
+     * @param isSoft          true if {@link SoftReference} elements are to
+     *                        be used, {@link WeakReference} otherwise.
+     * @param useNativeQueue  true if uses NativeReferenceQueue
+     *                        otherwise use {@link ReferenceQueue}.
+     * @param supplier        {@link Supplier} of the backing map
+     *
+     * @return a new set with {@link Reference} elements
+     *
+     * @param <E> the type of elements maintained by this set
+     */
+    public static <E> ReferencedKeySet<E>
+    create(boolean isSoft, boolean useNativeQueue, Supplier<Map<ReferenceKey<E>, ReferenceKey<E>>> supplier) {
+         return new ReferencedKeySet<>(ReferencedKeyMap.create(isSoft, useNativeQueue, supplier));
+    }
+
+    /**
+     * Removes enqueued weak references from set.
+     */
+    public void removeStaleReferences() {
+        map.removeStaleReferences();
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return map.keySet().iterator();
+    }
+
+    @Override
+    public int size() {
+        return map.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return map.isEmpty();
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public boolean contains(Object o) {
+        return map.containsKey((T)o);
+    }
+
+    @Override
+    public boolean add(T e) {
+        return intern(e) == null;
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        return map.remove(o) != null;
+    }
+
+    @Override
+    public void clear() {
+        map.clear();
+    }
+
+    /**
+     * Gets an existing element from the set, returning null if not present or
+     * the old element if previously added.
+     *
+     * @param e  element to get
+     *
+     * @return the old element if present, otherwise, null
+     */
+    public T get(T e) {
+        ReferenceKey<T> key = map.get(e);
+
+        return key == null ? null : key.get();
+    }
+
+    /**
+     * Intern an element to the set, returning the element if newly added or the
+     * old element if previously added.
+     *
+     * @param e  element to add
+     *
+     * @return the old element if present, otherwise, the new element
+     */
+    public T intern(T e) {
+        return ReferencedKeyMap.intern(map, e);
+    }
+
+    /**
+     * Intern an element to the set, returning the element if newly added or the
+     * old element if previously added.
+     *
+     * @param e         element to add
+     * @param interner  operation to apply to key before adding to set
+     *
+     * @return the old element if present, otherwise, the new element
+     *
+     * @implNote This version of intern should not be called during phase1
+     * using a lambda. Use an UnaryOperator instance instead.
+     */
+    public T intern(T e, UnaryOperator<T> interner) {
+        return ReferencedKeyMap.intern(map, e, interner);
+    }
+}

src/java.base/share/classes/jdk/internal/util/SoftReferenceKey.java

@@ -23,7 +23,7 @@
  * questions.
  */
 
-package java.lang.runtime;
+package jdk.internal.util;
 
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.SoftReference;
@@ -35,9 +35,6 @@ import java.util.Objects;
  * @param <T> key type
  *
  * @since 21
- *
- * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
- *          Do not rely on its availability.
  */
 final class SoftReferenceKey<T> extends SoftReference<T> implements ReferenceKey<T> {
     /**
@@ -76,6 +73,8 @@ final class SoftReferenceKey<T> extends SoftReference<T> implements ReferenceKey
         if (obj instanceof ReferenceKey<?> key) {
             obj = key.get();
         }
+        // Note: refersTo is insufficient since keys require equivalence.
+        // refersTo would also require a cast to type T.
         return Objects.equals(get(), obj);
     }
 

src/java.base/share/classes/jdk/internal/util/StrongReferenceKey.java

@@ -23,7 +23,7 @@
  * questions.
  */
 
-package java.lang.runtime;
+package jdk.internal.util;
 
 import java.util.Objects;
 
@@ -34,9 +34,6 @@ import java.util.Objects;
  * @param <T> key type
  *
  * @since 21
- *
- * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
- *          Do not rely on its availability.
  */
 final class StrongReferenceKey<T> implements ReferenceKey<T> {
     T key;

src/java.base/share/classes/jdk/internal/util/WeakReferenceKey.java

@@ -23,7 +23,7 @@
  * questions.
  */
 
-package java.lang.runtime;
+package jdk.internal.util;
 
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
@@ -35,9 +35,6 @@ import java.util.Objects;
  * @param <T> key type
  *
  * @since 21
- *
- * Warning: This class is part of PreviewFeature.Feature.STRING_TEMPLATES.
- *          Do not rely on its availability.
  */
 final class WeakReferenceKey<T> extends WeakReference<T> implements ReferenceKey<T> {
     /**
@@ -76,6 +73,8 @@ final class WeakReferenceKey<T> extends WeakReference<T> implements ReferenceKey
         if (obj instanceof ReferenceKey<?> key) {
             obj = key.get();
         }
+        // Note: refersTo is insufficient since keys require equivalence.
+        // refersTo would also require a cast to type T.
         return Objects.equals(get(), obj);
     }
 

test/jdk/java/lang/runtime/ReferencedKeyTest.java

@@ -1,109 +0,0 @@
-/*
- * Copyright (c) 2023, 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
- * @summary Test features provided by the ReferencedKeyMap class.
- * @modules java.base/java.lang.runtime
- * @enablePreview
- * @compile --patch-module java.base=${test.src} ReferencedKeyTest.java
- * @run main/othervm --patch-module java.base=${test.class.path} java.lang.runtime.ReferencedKeyTest
- */
-
-package java.lang.runtime;
-
-import java.util.HashMap;
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.function.Supplier;
-
-public class ReferencedKeyTest {
-    static long BASE_KEY = 10_000_000L;
-
-    public static void main(String[] args) throws Throwable {
-        mapTest(false, HashMap::new);
-        mapTest(true, HashMap::new);
-        mapTest(false, ConcurrentHashMap::new);
-        mapTest(true, ConcurrentHashMap::new);
-    }
-
-    static void assertTrue(boolean test, String message) {
-        if (!test) {
-            throw new RuntimeException(message);
-        }
-    }
-
-    static void  mapTest(boolean isSoft, Supplier<Map<ReferenceKey<Long>, String>> supplier) {
-        Map<Long, String> map = ReferencedKeyMap.create(isSoft, supplier);
-        populate(map);
-        collect();
-        // assertTrue(map.isEmpty() || isSoft, "Weak not collecting");
-        populate(map);
-        methods(map);
-    }
-
-    static void methods(Map<Long, String> map) {
-        assertTrue(map.size() == 26, "missing key");
-        assertTrue(map.containsKey(BASE_KEY + 'a' -'a'), "missing key");
-        assertTrue(map.get(BASE_KEY + 'b' -'a').equals("b"), "wrong key");
-        assertTrue(map.containsValue("c"), "missing value");
-        map.remove(BASE_KEY + 'd' -'a');
-        assertTrue(map.get(BASE_KEY + 'd' -'a') == null, "not removed");
-        map.putAll(Map.of(1L, "A", 2L, "B"));
-        assertTrue(map.get(2L).equals("B"), "collection not added");
-        assertTrue(map.keySet().contains(1L), "key missing");
-        assertTrue(map.values().contains("A"), "key missing");
-        assertTrue(map.entrySet().contains(Map.entry(1L, "A")), "key missing");
-        map.putIfAbsent(3L, "C");
-        assertTrue(map.get(3L).equals("C"), "key missing");
-        map.putIfAbsent(2L, "D");
-        assertTrue(map.get(2L).equals("B"), "key replaced");
-        map.remove(3L);
-        assertTrue(map.get(3L) == null, "key not removed");
-        map.replace(2L, "D");
-        assertTrue(map.get(2L).equals("D"), "key not replaced");
-        map.replace(2L, "B", "E");
-        assertTrue(map.get(2L).equals("D"), "key replaced");
-    }
-
-    static void collect() {
-        System.gc();
-        sleep();
-    }
-
-    static void sleep() {
-        try {
-            Thread.sleep(100L);
-        } catch (InterruptedException e) {
-            throw new RuntimeException(e);
-        }
-    }
-
-    static void populate(Map<Long, String> map) {
-        for (int i = 0; i < 26; i++) {
-            Long key = BASE_KEY + i;
-            String value = String.valueOf((char) ('a' + i));
-            map.put(key, value);
-        }
-    }
-}

test/jdk/jdk/internal/util/ReferencedKeyTest.java

@@ -0,0 +1,175 @@
+/*
+ * Copyright (c) 2023, 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 8285932 8310913
+ * @summary Test features provided by the ReferencedKeyMap/ReferencedKeySet classes.
+ * @modules java.base/jdk.internal.util
+ * @compile --patch-module java.base=${test.src} ReferencedKeyTest.java
+ * @run main/othervm --patch-module java.base=${test.class.path} jdk.internal.util.ReferencedKeyTest
+ */
+
+package jdk.internal.util;
+
+import java.lang.ref.PhantomReference;
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.BooleanSupplier;
+import java.util.function.Supplier;
+
+public class ReferencedKeyTest {
+    static long BASE_KEY = 10_000_000L;
+
+    public static void main(String[] args) {
+        mapTest(false, HashMap::new);
+        mapTest(true, HashMap::new);
+        mapTest(false, ConcurrentHashMap::new);
+        mapTest(true, ConcurrentHashMap::new);
+
+        setTest(false, HashMap::new);
+        setTest(true, HashMap::new);
+        setTest(false, ConcurrentHashMap::new);
+        setTest(true, ConcurrentHashMap::new);
+    }
+
+    static void assertTrue(boolean test, String message) {
+        if (!test) {
+            throw new RuntimeException(message);
+        }
+    }
+
+    static void mapTest(boolean isSoft, Supplier<Map<ReferenceKey<Long>, String>> supplier) {
+        Map<Long, String> map = ReferencedKeyMap.create(isSoft, supplier);
+        populate(map);
+        if (!isSoft) {
+            if (!collect(() -> map.isEmpty())) {
+                throw new RuntimeException("WeakReference map not collecting!");
+            }
+        }
+        populate(map);
+        methods(map);
+    }
+
+    static void setTest(boolean isSoft, Supplier<Map<ReferenceKey<Long>, ReferenceKey<Long>>> supplier) {
+        ReferencedKeySet<Long> set = ReferencedKeySet.create(isSoft, supplier);
+        populate(set);
+        if (!isSoft) {
+            if (!collect(() -> set.isEmpty())) {
+                throw new RuntimeException("WeakReference set not collecting!");
+            }
+        }
+        populate(set);
+        methods(set);
+    }
+
+    static void methods(Map<Long, String> map) {
+        assertTrue(map.size() == 26, "missing key");
+        assertTrue(map.containsKey(BASE_KEY + 'a' -'a'), "missing key");
+        assertTrue(map.get(BASE_KEY + 'b' -'a').equals("b"), "wrong key");
+        assertTrue(map.containsValue("c"), "missing value");
+        map.remove(BASE_KEY + 'd' -'a');
+        assertTrue(map.get(BASE_KEY + 'd' -'a') == null, "not removed");
+        map.putAll(Map.of(1L, "A", 2L, "B"));
+        assertTrue(map.get(2L).equals("B"), "collection not added");
+        assertTrue(map.containsKey(1L), "key missing");
+        assertTrue(map.containsValue("A"), "key missing");
+        assertTrue(map.entrySet().contains(Map.entry(1L, "A")), "key missing");
+        map.putIfAbsent(3L, "C");
+        assertTrue(map.get(3L).equals("C"), "key missing");
+        map.putIfAbsent(2L, "D");
+        assertTrue(map.get(2L).equals("B"), "key replaced");
+        map.remove(3L);
+        assertTrue(map.get(3L) == null, "key not removed");
+        map.replace(2L, "D");
+        assertTrue(map.get(2L).equals("D"), "key not replaced");
+        map.replace(2L, "B", "E");
+        assertTrue(map.get(2L).equals("D"), "key replaced");
+    }
+
+    static void methods(ReferencedKeySet<Long> set) {
+        assertTrue(set.size() == 26, "missing key");
+        assertTrue(set.contains(BASE_KEY + 3), "missing key");
+        set.remove(BASE_KEY + 3);
+        assertTrue(!set.contains(BASE_KEY + 3), "not removed");
+        Long element1 = set.get(BASE_KEY + 2);
+        Long element2 = set.get(BASE_KEY + 3);
+        Long element3 = set.get(BASE_KEY + 4);
+        Long intern1 = set.intern(BASE_KEY + 2);
+        Long intern2 = set.intern(BASE_KEY + 3);
+        Long intern3 = set.intern(BASE_KEY + 4, e -> e);
+        assertTrue(element1 != null, "missing key");
+        assertTrue(element2 == null, "not removed");
+        assertTrue(element1 == intern1, "intern failed"); // must be same object
+        assertTrue(intern2 != null, "intern failed");
+        assertTrue(element3 == intern3, "intern failed");
+    }
+
+    // Borrowed from jdk.test.lib.util.ForceGC but couldn't use from java.base/jdk.internal.util
+    static boolean collect(BooleanSupplier booleanSupplier) {
+        ReferenceQueue<Object> queue = new ReferenceQueue<>();
+        Object obj = new Object();
+        PhantomReference<Object> ref = new PhantomReference<>(obj, queue);
+        obj = null;
+        Reference.reachabilityFence(obj);
+        Reference.reachabilityFence(ref);
+        long timeout = 1000L;
+        long quanta = 200L;
+        long retries = timeout / quanta;
+
+        for (; retries >= 0; retries--) {
+            if (booleanSupplier.getAsBoolean()) {
+                return true;
+            }
+
+            System.gc();
+
+            try {
+                queue.remove(quanta);
+            } catch (InterruptedException ie) {
+                // ignore, the loop will try again
+            }
+        }
+
+        return booleanSupplier.getAsBoolean();
+    }
+
+    static void populate(Map<Long, String> map) {
+        for (int i = 0; i < 26; i++) {
+            Long key = BASE_KEY + i;
+            String value = String.valueOf((char) ('a' + i));
+            map.put(key, value);
+        }
+    }
+
+    static void populate(Set<Long> set) {
+        for (int i = 0; i < 26; i++) {
+            Long value = BASE_KEY + i;
+            set.add(value);
+        }
+    }
+}