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/***** BEGIN LICENSE BLOCK *****
 * Version: EPL 1.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * License Version 1.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.eclipse.org/legal/epl-v10.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * 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 
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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package org.jruby.util.collections;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Map-like that holds its values weakly (backed by a concurrent hash map).
 */
public class WeakValuedMap {

    private final Map> map = newMap();
    @SuppressWarnings("unchecked")
    private final ReferenceQueue deadRefs = new ReferenceQueue();

    public final void put(Key key, Value value) {
        cleanReferences();
        map.put(key, new KeyedReference(value, key, deadRefs));
    }

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

    protected Map> newMap() {
        return new ConcurrentHashMap>();
    }

    protected static class KeyedReference extends WeakReference {

        protected final Key key;

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

    }

    @SuppressWarnings("unchecked")
    private void cleanReferences() {
        KeyedReference ref;
        while ( ( ref = (KeyedReference) deadRefs.poll() ) != null ) {
            map.remove( ref.key );
        }
    }
}