001/**
002 * Copyright The Apache Software Foundation
003 *
004 * Licensed to the Apache Software Foundation (ASF) under one or more
005 * contributor license agreements. See the NOTICE file distributed with this
006 * work for additional information regarding copyright ownership. The ASF
007 * licenses this file to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance with the License.
009 * You may obtain a copy of the License at
010 *
011 * http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
015 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
016 * License for the specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.hadoop.hbase.io.hfile;
020
021import java.util.Map;
022import java.util.concurrent.ConcurrentHashMap;
023import java.util.concurrent.atomic.AtomicInteger;
024import java.util.stream.Collectors;
025
026import org.apache.yetus.audience.InterfaceAudience;
027
028/**
029 * This class is used to manage the identifiers for {@link CacheableDeserializer}.
030 * All deserializers are registered with this Manager via the
031 * {@link #registerDeserializer(CacheableDeserializer)}}. On registration, we return an
032 * int *identifier* for this deserializer. The int identifier is passed to
033 * {@link #getDeserializer(int)}} to obtain the registered deserializer instance.
034 */
035@InterfaceAudience.Private
036public class CacheableDeserializerIdManager {
037  private static final Map<Integer, CacheableDeserializer<Cacheable>> registeredDeserializers =
038      new ConcurrentHashMap<>();
039  private static final AtomicInteger identifier = new AtomicInteger(0);
040
041  /**
042   * Register the given {@link Cacheable} -- usually an hfileblock instance, these implement
043   * the Cacheable Interface -- deserializer and generate a unique identifier id for it and return
044   * this as our result.
045   * @return the identifier of given cacheable deserializer
046   * @see #getDeserializer(int)
047   */
048  public static int registerDeserializer(CacheableDeserializer<Cacheable> cd) {
049    int idx = identifier.incrementAndGet();
050    // No synchronization here because keys will be unique
051    registeredDeserializers.put(idx, cd);
052    return idx;
053  }
054
055  /**
056   * Get the cacheable deserializer registered at the given identifier Id.
057   * @see #registerDeserializer(CacheableDeserializer)
058   */
059  public static CacheableDeserializer<Cacheable> getDeserializer(int id) {
060    return registeredDeserializers.get(id);
061  }
062
063  /**
064   * Snapshot a map of the current identifiers to class names for reconstruction on reading out
065   * of a file.
066   */
067  public static Map<Integer,String> save() {
068    // No synchronization here because weakly consistent view should be good enough
069    // The assumed risk is that we might not see a new serializer that comes in while iterating,
070    // but with a synchronized block, we won't see it anyway
071    return registeredDeserializers.entrySet().stream()
072        .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().getClass().getName()));
073  }
074}