com.analog.lyric.collect.WeakInterner.java Source code

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/*******************************************************************************
*   Copyright 2014 Analog Devices, Inc.
*
*   Licensed 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
*
*       http://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.analog.lyric.collect;

import java.lang.ref.WeakReference;
import java.util.WeakHashMap;

import net.jcip.annotations.ThreadSafe;

import org.eclipse.jdt.annotation.NonNullByDefault;
import com.google.common.collect.Interner;

/**
 * An {@link Interner} that weakly caches interned values.
 * <p>
 * This duplicates the functionality of {@linkplain com.google.common.collect.Interners#newWeakInterner
 * Interners.newWeakInterner()} from the Guava library. It is really only needed to work around a bug
 * in MATLAB.
 * <p>
 * @since 0.07
 * @author Christopher Barber
 */
@ThreadSafe
public class WeakInterner<E> implements Interner<E> {
    private final WeakHashMap<E, WeakReference<E>> _interned = new WeakHashMap<>();

    /**
     * Create a new interner for type {@code T}
     * @since 0.07
     */
    public static <T> WeakInterner<T> create() {
        return new WeakInterner<T>();
    }

    @NonNullByDefault(false)
    @Override
    public E intern(E value) {
        synchronized (this) {
            final WeakReference<E> ref = _interned.get(value);
            if (ref != null) {
                E internedValue = ref.get();
                if (internedValue != null) {
                    return internedValue;
                }
            }

            _interned.put(value, new WeakReference<E>(value));
        }

        return value;
    }

}