existing = setMap.map.putIfAbsent(entryKey, entryKey);
+ if (existing == null) {
+ return true;
+ } 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.
+ entryKey.unused();
+ return false;
+ }
+ }
+
}
diff --git a/src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java b/src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java
new file mode 100644
index 00000000000..21b940439e0
--- /dev/null
+++ b/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}.
+ *
+ * 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 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 the type of elements maintained by this set
+ */
+public final class ReferencedKeySet extends AbstractSet {
+ /**
+ * Backing {@link ReferencedKeySet} map.
+ */
+ final ReferencedKeyMap> map;
+
+ /**
+ * Private constructor.
+ *
+ * @param map backing map
+ */
+ private ReferencedKeySet(ReferencedKeyMap> 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 the type of elements maintained by this set
+ */
+ public static ReferencedKeySet
+ create(boolean isSoft, Supplier, ReferenceKey>> 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