BasePackBitmapIndex.java

/*
 * Copyright (C) 2012, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.file;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectIdOwnerMap;

import com.googlecode.javaewah.EWAHCompressedBitmap;

/**
 * Base implementation of the PackBitmapIndex.
 */
abstract class BasePackBitmapIndex extends PackBitmapIndex {
    private final ObjectIdOwnerMap<StoredBitmap> bitmaps;

    BasePackBitmapIndex(ObjectIdOwnerMap<StoredBitmap> bitmaps) {
        this.bitmaps = bitmaps;
    }

    /** {@inheritDoc} */
    @Override
    public EWAHCompressedBitmap getBitmap(AnyObjectId objectId) {
        StoredBitmap sb = bitmaps.get(objectId);
        return sb != null ? sb.getBitmap() : null;
    }

    ObjectIdOwnerMap<StoredBitmap> getBitmaps() {
        return bitmaps;
    }

    /**
     * Data representation of the bitmap entry restored from a pack index. The
     * commit of the bitmap is the map key.
     */
    static final class StoredBitmap extends ObjectIdOwnerMap.Entry {
        private volatile Object bitmapContainer;
        private final int flags;

        StoredBitmap(AnyObjectId objectId, EWAHCompressedBitmap bitmap,
                StoredBitmap xorBitmap, int flags) {
            super(objectId);
            this.bitmapContainer = xorBitmap == null
                    ? bitmap
                    : new XorCompressedBitmap(bitmap, xorBitmap);
            this.flags = flags;
        }

        /**
         * Computes and returns the full bitmap.
         *
         * @return the full bitmap
         */
        EWAHCompressedBitmap getBitmap() {
            EWAHCompressedBitmap bitmap = getBitmapWithoutCaching();
            // Cache the result.
            bitmapContainer = bitmap;
            return bitmap;
        }

        /**
         * Compute and return the full bitmap, do NOT cache the expanded bitmap,
         * which saves memory and should only be used during bitmap creation in
         * garbage collection.
         *
         * @return the full bitmap
         */
        EWAHCompressedBitmap getBitmapWithoutCaching() {
            // Fast path to immediately return the expanded result.
            Object r = bitmapContainer;
            if (r instanceof EWAHCompressedBitmap)
                return (EWAHCompressedBitmap) r;

            // Expand the bitmap but not cache the result.
            XorCompressedBitmap xb = (XorCompressedBitmap) r;
            EWAHCompressedBitmap out = xb.bitmap;
            for (;;) {
                r = xb.xorBitmap.bitmapContainer;
                if (r instanceof EWAHCompressedBitmap) {
                    out = out.xor((EWAHCompressedBitmap) r);
                    out.trim();
                    return out;
                }
                xb = (XorCompressedBitmap) r;
                out = out.xor(xb.bitmap);
            }
        }

        /** @return the flags associated with the bitmap */
        int getFlags() {
            return flags;
        }
    }

    private static final class XorCompressedBitmap {
        final EWAHCompressedBitmap bitmap;
        final StoredBitmap xorBitmap;

        XorCompressedBitmap(EWAHCompressedBitmap b, StoredBitmap xb) {
            bitmap = b;
            xorBitmap = xb;
        }
    }
}