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/*
 * 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.hadoop.hbase.regionserver;

import java.io.IOException;
import java.util.List;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionContext;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionPolicy;
import org.apache.hadoop.hbase.regionserver.compactions.Compactor;
import org.apache.hadoop.hbase.util.ReflectionUtils;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * StoreEngine is a factory that can create the objects necessary for HStore to operate. Since not
 * all compaction policies, compactors and store file managers are compatible, they are tied
 * together and replaced together via StoreEngine-s.
 */
@InterfaceAudience.Private
public abstract class StoreEngine {
  protected SF storeFlusher;
  protected CP compactionPolicy;
  protected C compactor;
  protected SFM storeFileManager;

  /**
   * The name of the configuration parameter that specifies the class of a store engine that is used
   * to manage and compact HBase store files.
   */
  public static final String STORE_ENGINE_CLASS_KEY = "hbase.hstore.engine.class";

  private static final Class> DEFAULT_STORE_ENGINE_CLASS =
    DefaultStoreEngine.class;

  /** Returns Compaction policy to use. */
  public CompactionPolicy getCompactionPolicy() {
    return this.compactionPolicy;
  }

  /** Returns Compactor to use. */
  public Compactor getCompactor() {
    return this.compactor;
  }

  /** Returns Store file manager to use. */
  public StoreFileManager getStoreFileManager() {
    return this.storeFileManager;
  }

  /** Returns Store flusher to use. */
  public StoreFlusher getStoreFlusher() {
    return this.storeFlusher;
  }

  /**
   * @param filesCompacting Files currently compacting
   * @return whether a compaction selection is possible
   */
  public abstract boolean needsCompaction(List filesCompacting);

  /**
   * Creates an instance of a compaction context specific to this engine. Doesn't actually select or
   * start a compaction. See CompactionContext class comment.
   * @return New CompactionContext object.
   */
  public abstract CompactionContext createCompaction() throws IOException;

  /**
   * Create the StoreEngine's components.
   */
  protected abstract void createComponents(Configuration conf, HStore store,
    CellComparator cellComparator) throws IOException;

  private void createComponentsOnce(Configuration conf, HStore store, CellComparator cellComparator)
    throws IOException {
    assert compactor == null && compactionPolicy == null && storeFileManager == null
      && storeFlusher == null;
    createComponents(conf, store, cellComparator);
    assert compactor != null && compactionPolicy != null && storeFileManager != null
      && storeFlusher != null;
  }

  /**
   * Create the StoreEngine configured for the given Store.
   * @param store          The store. An unfortunate dependency needed due to it being passed to
   *                       coprocessors via the compactor.
   * @param conf           Store configuration.
   * @param cellComparator CellComparator for storeFileManager.
   * @return StoreEngine to use.
   */
  public static StoreEngine create(HStore store, Configuration conf,
    CellComparator cellComparator) throws IOException {
    String className = conf.get(STORE_ENGINE_CLASS_KEY, DEFAULT_STORE_ENGINE_CLASS.getName());
    try {
      StoreEngine se =
        ReflectionUtils.instantiateWithCustomCtor(className, new Class[] {}, new Object[] {});
      se.createComponentsOnce(conf, store, cellComparator);
      return se;
    } catch (Exception e) {
      throw new IOException("Unable to load configured store engine '" + className + "'", e);
    }
  }
}