trunk/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/tar/CleanupContext.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.jackrabbit.oak.segment.file.tar;

import java.util.Collection;
import java.util.UUID;

/**
 * Initial data and logic needed for the cleanup of unused TAR entries.
 */
public interface CleanupContext {

    /**
     * Initial references to TAR entries. These references represent the entries
     * that are currently in use. The transitive closure of these entries will
     * be computed by the cleanup algorithm.
     *
     * @return An instance of {@link Collection}.
     */
    Collection<UUID> initialReferences();

    /**
     * Check if an entry should be reclaimed.
     *
     * @param id         The identifier of the entry.
     * @param generation The generation of the entry.
     * @param referenced If this entry was referenced directly or indirectly by
     *                   the initial set of references.
     * @return {@code true} if the entry should be reclaimed, {@code false}
     * otherwise.
     */
    boolean shouldReclaim(UUID id, GCGeneration generation, boolean referenced);

    /**
     * Determine if a reference between two entries should be followed, and if
     * the referenced entry should be marked.
     *
     * @param from The identifier of the referencing entry.
     * @param to   The identifier of the referenced entry.
     * @return {@code true} if the reference should be followed, {@code false}
     * otherwise.
     */
    boolean shouldFollow(UUID from, UUID to);

}