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 * Copyright (C) 2002-2004 Jan Arne Petersen 
 * Copyright (C) 2002-2004 Anders Bengtsson 
 * Copyright (C) 2004-2006 Charles O Nutter 
 * Copyright (C) 2004 Stefan Matthias Aust 
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package org.jruby.util.collections;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.IdentityHashMap;
import java.util.Map;

/**
 * A Map that holds its values weakly and uses object identity for keys.
 */
public class WeakValuedIdentityMap {
    private final ReferenceQueue deadReferences = new ReferenceQueue();
    private final Map> references = new IdentityHashMap>();

    public synchronized void put(Key key, Value value) {
        cleanReferences();
        references.put(key, new KeyedReference(value, key, deadReferences));
    }

    public synchronized Value get(Key key) {
        cleanReferences();
        KeyedReference reference = references.get(key);
        if (reference == null) {
            return null;
        }
        return reference.get();
    }

    private void cleanReferences() {
        KeyedReference ref;
        while ((ref = (KeyedReference) deadReferences.poll()) != null) {
            references.remove((ref.key()));
        }
    }

    private static class KeyedReference extends WeakReference {
        private final Key key;

        public KeyedReference(Value object, Key key, ReferenceQueue queue) {
            super(object, queue);
            this.key = key;
        }

        public Key key() {
            return key;
        }
    }
}