src/com/android/gallery3d/util/IdentityCache.java

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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.android.gallery3d.util;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Set;

public class IdentityCache<K, V> {

    private final HashMap<K, Entry<K, V>> mWeakMap =
            new HashMap<K, Entry<K, V>>();
    private ReferenceQueue<V> mQueue = new ReferenceQueue<V>();

    public IdentityCache() {
    }

    private static class Entry<K, V> extends WeakReference<V> {
        K mKey;

        public Entry(K key, V value, ReferenceQueue<V> queue) {
            super(value, queue);
            mKey = key;
        }
    }

    private void cleanUpWeakMap() {
        Entry<K, V> entry = (Entry<K, V>) mQueue.poll();
        while (entry != null) {
            mWeakMap.remove(entry.mKey);
            entry = (Entry<K, V>) mQueue.poll();
        }
    }

    public synchronized V put(K key, V value) {
        cleanUpWeakMap();
        Entry<K, V> entry = mWeakMap.put(
                key, new Entry<K, V>(key, value, mQueue));
        return entry == null ? null : entry.get();
    }

    public synchronized V get(K key) {
        cleanUpWeakMap();
        Entry<K, V> entry = mWeakMap.get(key);
        return entry == null ? null : entry.get();
    }

    // This is currently unused.
    /*
    public synchronized void clear() {
        mWeakMap.clear();
        mQueue = new ReferenceQueue<V>();
    }
    */

    // This is for debugging only
    public synchronized ArrayList<K> keys() {
        Set<K> set = mWeakMap.keySet();
        ArrayList<K> result = new ArrayList<K>(set);
        return result;
    }
}