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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.awt.image;

import java.awt.*;
import java.lang.ref.*;
import java.util.*;
import java.util.concurrent.locks.*;
import sun.awt.AppContext;

ImageCache - A fixed pixel count sized cache of Images keyed by arbitrary
set of arguments. All images are held with SoftReferences so they will be
dropped by the GC if heap memory gets tight. When our size hits max pixel
count least recently requested images are removed first.
The ImageCache must be used from the thread with an AppContext only.
/**
 * ImageCache - A fixed pixel count sized cache of Images keyed by arbitrary
 * set of arguments. All images are held with SoftReferences so they will be
 * dropped by the GC if heap memory gets tight. When our size hits max pixel
 * count least recently requested images are removed first.
 *
 * The ImageCache must be used from the thread with an AppContext only.
 *
 */
final public class ImageCache {

    // Ordered Map keyed by args hash, ordered by most recent accessed entry.
    private final LinkedHashMap<PixelsKey, ImageSoftReference> map
            = new LinkedHashMap<>(16, 0.75f, true);

    // Maximum number of pixels to cache, this is used if maxCount
    private final int maxPixelCount;
    // The current number of pixels stored in the cache
    private int currentPixelCount = 0;

    // Lock for concurrent access to map
    private final ReadWriteLock lock = new ReentrantReadWriteLock();
    // Reference queue for tracking lost softreferences to images in the cache
    private final ReferenceQueue<Image> referenceQueue = new ReferenceQueue<>();

    public static ImageCache getInstance() {
        return AppContext.getSoftReferenceValue(ImageCache.class,
                () -> new ImageCache());
    }

    ImageCache(final int maxPixelCount) {
        this.maxPixelCount = maxPixelCount;
    }

    ImageCache() {
        this((8 * 1024 * 1024) / 4); // 8Mb of pixels
    }

    public void flush() {
        lock.writeLock().lock();
        try {
            map.clear();
        } finally {
            lock.writeLock().unlock();
        }
    }

    public Image getImage(final PixelsKey key){
        final ImageSoftReference ref;
        lock.readLock().lock();
        try {
            ref = map.get(key);
        } finally {
            lock.readLock().unlock();
        }
        return ref == null ? null : ref.get();
    }

    
Sets the cached image for the specified constraints.
Params:
key – The key with which the specified image is to be associated
image –  The image to store in cache/**
     * Sets the cached image for the specified constraints.
     *
     * @param key The key with which the specified image is to be associated
     * @param image  The image to store in cache
     */
    public void setImage(final PixelsKey key, final Image image) {

        lock.writeLock().lock();
        try {
            ImageSoftReference ref = map.get(key);

            // check if currently in map
            if (ref != null) {
                if (ref.get() != null) {
                    return;
                }
                // soft image has been removed
                currentPixelCount -= key.getPixelCount();
                map.remove(key);
            };


            // add new image to pixel count
            final int newPixelCount = key.getPixelCount();
            currentPixelCount += newPixelCount;
            // clean out lost references if not enough space
            if (currentPixelCount > maxPixelCount) {
                while ((ref = (ImageSoftReference)referenceQueue.poll()) != null) {
                    //reference lost
                    map.remove(ref.key);
                    currentPixelCount -= ref.key.getPixelCount();
                }
            }

            // remove old items till there is enough free space
            if (currentPixelCount > maxPixelCount) {
                final Iterator<Map.Entry<PixelsKey, ImageSoftReference>>
                        mapIter = map.entrySet().iterator();
                while ((currentPixelCount > maxPixelCount) && mapIter.hasNext()) {
                    final Map.Entry<PixelsKey, ImageSoftReference> entry =
                            mapIter.next();
                    mapIter.remove();
                    final Image img = entry.getValue().get();
                    if (img != null) img.flush();
                    currentPixelCount -= entry.getValue().key.getPixelCount();
                }
            }

            // finally put new in map
            map.put(key, new ImageSoftReference(key, image, referenceQueue));
        } finally {
            lock.writeLock().unlock();
        }
    }

    public interface PixelsKey {

        int getPixelCount();
    }

    private static class ImageSoftReference extends SoftReference<Image> {

        final PixelsKey key;

        ImageSoftReference(final PixelsKey key, final Image referent,
                final ReferenceQueue<? super Image> q) {
            super(referent, q);
            this.key = key;
        }
    }
}