/**
    *
    * 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.wal;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.wal.RegionGroupingProvider.RegionGroupingStrategy;
  
  /**
   * A WAL grouping strategy that limits the number of wal groups to
   * "hbase.wal.regiongrouping.numgroups".
   */
  @InterfaceAudience.Private
  public class BoundedGroupingStrategy implements RegionGroupingStrategy{
  
    static final String NUM_REGION_GROUPS = "hbase.wal.regiongrouping.numgroups";
    static final int DEFAULT_NUM_REGION_GROUPS = 2;
  
    private ConcurrentHashMap<String, String> groupNameCache =
        new ConcurrentHashMap<String, String>();
    private AtomicInteger counter = new AtomicInteger(0);
    private String[] groupNames;
  
    @Override
    public String group(byte[] identifier, byte[] namespace) {
      String idStr = Bytes.toString(identifier);
      String groupName = groupNameCache.get(idStr);
      if (null == groupName) {
        groupName = groupNames[getAndIncrAtomicInteger(counter, groupNames.length)];
        String extantName = groupNameCache.putIfAbsent(idStr, groupName);
        if (extantName != null) {
          return extantName;
        }
      }
      return groupName;
    }
  
    // Non-blocking incrementing & resetting of AtomicInteger.
    private int getAndIncrAtomicInteger(AtomicInteger atomicInt, int reset) {
      for (;;) {
        int current = atomicInt.get();
        int next = (current + 1);
        if (next == reset) {
          next = 0;
        }
        if (atomicInt.compareAndSet(current, next)) return current;
      }
    }
  
    @Override
    public void init(Configuration config, String providerId) {
      int regionGroupNumber = config.getInt(NUM_REGION_GROUPS, DEFAULT_NUM_REGION_GROUPS);
      groupNames = new String[regionGroupNumber];
      for (int i = 0; i < regionGroupNumber; i++) {
        groupNames[i] = "regiongroup-" + i;
      }
    }
  
  }