Add WeakIdentityHashMap implementation (from Apache Avro)

Origin <https://github.com/apache/avro/blob/master/lang/java/avro/src/main/java/org/apache/avro/util/WeakIdentityHashMap.java>
from their commit 70260919426f89825ca148f5ee815f3b2cf4764d.
Apache License Version 2.0 until.
Using our JogAmp 'New BSD 2-Clause License' for changes after this initial commit.

Related to Bug 1312, where we like to utilize a WeakIdentityHashMap,
allowing to have cached shared GLContext to disappear .. a compromise.

Author: sgothel

LICENSE.txt

@@ -140,8 +140,8 @@ L.3) The GlueGen source tree contains CGRAM http://www.antlr.org/grammar/cgram/,
 A.1) The GlueGen source tree contains code from The Apache Software Foundation
      which is covered by the Apache License Version 2.0
 
-   Apache Harmony - Open Source Java SE
-   =====================================
+A.1.1) Apache Harmony - Open Source Java SE
+   ===============================================
 
    <http://harmony.apache.org/>
 
@@ -157,6 +157,25 @@ A.1) The GlueGen source tree contains code from The Apache Software Foundation
     - src/java/com/jogamp/common/net/Uri.java 
       (derived from java.net.URI.Helper and heavily modified)
 
+A.1.2) Apache Avro - A data serialization system.
+   ===============================================
+
+   <https://avro.apache.org/>
+
+   Copyright 2010-2019 The Apache Software Foundation
+
+   Apache License Version 2.0, January 2004
+   http://www.apache.org/licenses/LICENSE-2.0
+   Or within this repository: doc/licenses/Apache.LICENSE-2.0
+
+   Files:
+    - src/java/com/jogamp/common/util/WeakIdentityHashMap.java
+
+      <https://github.com/apache/avro/blob/master/lang/java/avro/src/main/java/org/apache/avro/util/WeakIdentityHashMap.java>
+      Taken as commit 70260919426f89825ca148f5ee815f3b2cf4764d
+      and using our JogAmp 'New BSD 2-Clause License' since migration.
+
+
 A.2) The GlueGen source tree contains code from Ben Mankin, a.k.a 'Shevek',
      which is covered by the Apache License Version 2.0
 

src/java/com/jogamp/common/util/WeakIdentityHashMap.java

@@ -0,0 +1,229 @@
+/**
+ * Copyright 2019 JogAmp Community. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are
+ * permitted provided that the following conditions are met:
+ *
+ *    1. Redistributions of source code must retain the above copyright notice, this list of
+ *       conditions and the following disclaimer.
+ *
+ *    2. Redistributions in binary form must reproduce the above copyright notice, this list
+ *       of conditions and the following disclaimer in the documentation and/or other materials
+ *       provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY JogAmp Community ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JogAmp Community OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * The views and conclusions contained in the software and documentation are those of the
+ * authors and should not be interpreted as representing official policies, either expressed
+ * or implied, of JogAmp Community.
+ *
+ * Original source code of this class taken from Apache Avro
+ * <https://github.com/apache/avro/blob/master/lang/java/avro/src/main/java/org/apache/avro/util/WeakIdentityHashMap.java>
+ * commit 70260919426f89825ca148f5ee815f3b2cf4764d.
+ * Up until commit 70260919426f89825ca148f5ee815f3b2cf4764d, 
+ * this code has been licensed as described below:
+ * 
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package com.jogamp.common.util;
+
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.WeakReference;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Implements a combination of WeakHashMap and IdentityHashMap. Useful for
+ * caches that need to key off of a == comparison instead of a .equals.
+ *
+ * <b> This class is not a general-purpose Map implementation! While this class
+ * implements the Map interface, it intentionally violates Map's general
+ * contract, which mandates the use of the equals method when comparing objects.
+ * This class is designed for use only in the rare cases wherein
+ * reference-equality semantics are required.
+ *
+ * Note that this implementation is not synchronized. </b>
+ */
+public class WeakIdentityHashMap<K, V> implements Map<K, V> {
+  private final ReferenceQueue<K> queue = new ReferenceQueue<>();
+  private Map<IdentityWeakReference, V> backingStore = new HashMap<>();
+
+  public WeakIdentityHashMap() {
+  }
+
+  @Override
+  public void clear() {
+    backingStore.clear();
+    reap();
+  }
+
+  @Override
+  public boolean containsKey(Object key) {
+    reap();
+    return backingStore.containsKey(new IdentityWeakReference(key));
+  }
+
+  @Override
+  public boolean containsValue(Object value) {
+    reap();
+    return backingStore.containsValue(value);
+  }
+
+  @Override
+  public Set<Map.Entry<K, V>> entrySet() {
+    reap();
+    Set<Map.Entry<K, V>> ret = new HashSet<>();
+    for (Map.Entry<IdentityWeakReference, V> ref : backingStore.entrySet()) {
+      final K key = ref.getKey().get();
+      final V value = ref.getValue();
+      Map.Entry<K, V> entry = new Map.Entry<K, V>() {
+        @Override
+        public K getKey() {
+          return key;
+        }
+
+        @Override
+        public V getValue() {
+          return value;
+        }
+
+        @Override
+        public V setValue(V value) {
+          throw new UnsupportedOperationException();
+        }
+      };
+      ret.add(entry);
+    }
+    return Collections.unmodifiableSet(ret);
+  }
+
+  @Override
+  public Set<K> keySet() {
+    reap();
+    Set<K> ret = new HashSet<>();
+    for (IdentityWeakReference ref : backingStore.keySet()) {
+      ret.add(ref.get());
+    }
+    return Collections.unmodifiableSet(ret);
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof WeakIdentityHashMap)) {
+      return false;
+    }
+    return backingStore.equals(((WeakIdentityHashMap) o).backingStore);
+  }
+
+  @Override
+  public V get(Object key) {
+    reap();
+    return backingStore.get(new IdentityWeakReference(key));
+  }
+
+  @Override
+  public V put(K key, V value) {
+    reap();
+    return backingStore.put(new IdentityWeakReference(key), value);
+  }
+
+  @Override
+  public int hashCode() {
+    reap();
+    return backingStore.hashCode();
+  }
+
+  @Override
+  public boolean isEmpty() {
+    reap();
+    return backingStore.isEmpty();
+  }
+
+  @Override
+  public void putAll(Map t) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public V remove(Object key) {
+    reap();
+    return backingStore.remove(new IdentityWeakReference(key));
+  }
+
+  @Override
+  public int size() {
+    reap();
+    return backingStore.size();
+  }
+
+  @Override
+  public Collection<V> values() {
+    reap();
+    return backingStore.values();
+  }
+
+  private synchronized void reap() {
+    Object zombie = queue.poll();
+
+    while (zombie != null) {
+      IdentityWeakReference victim = (IdentityWeakReference) zombie;
+      backingStore.remove(victim);
+      zombie = queue.poll();
+    }
+  }
+
+  class IdentityWeakReference extends WeakReference<K> {
+    int hash;
+
+    @SuppressWarnings("unchecked")
+    IdentityWeakReference(Object obj) {
+      super((K) obj, queue);
+      hash = System.identityHashCode(obj);
+    }
+
+    @Override
+    public int hashCode() {
+      return hash;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (!(o instanceof WeakIdentityHashMap.IdentityWeakReference)) {
+        return false;
+      }
+      IdentityWeakReference ref = (IdentityWeakReference) o;
+      return this.get() == ref.get();
+    }
+  }
+}