content: package act.db.util;
  
  /*-
   * #%L
   * ACT Framework
   * %%
   * Copyright (C) 2014 - 2017 ActFramework
   * %%
   * Licensed 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.
   * #L%
   */
  
  import act.app.DbServiceManager;
  import act.conf.AppConfig;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * Define the interface that can generate next or retrieve current sequence number
   */
  public interface _SequenceNumberGenerator {
      /**
       * Generate next sequence number
       * @param name the name of the sequence
       * @return the next sequence number
       */
      long next(String name);
  
      /**
       * Returns the current sequence number
       * @param name the name of the sequence
       * @return the current sequence number
       */
      long get(String name);
  
      /**
       * Configure the sequence generator
       */
      void configure(AppConfig config, DbServiceManager dbManager);
  
      class InMemorySequenceNumberGenerator implements _SequenceNumberGenerator {
  
          private ConcurrentMap<String, AtomicLong> seqs = new ConcurrentHashMap<String, AtomicLong>();
          @Override
          public long next(String name) {
              return getSeq(name).getAndIncrement();
          }
  
          @Override
          public long get(String name) {
              return getSeq(name).get();
          }
  
          private AtomicLong getSeq(String name) {
              AtomicLong al = seqs.get(name);
              if (null == al) {
                  AtomicLong newAl = new AtomicLong(0);
                  al = seqs.putIfAbsent(name, newAl);
                  if (null == al) {
                      al = newAl;
                  }
              }
              return al;
          }
  
          @Override
          public void configure(AppConfig config, DbServiceManager dbManager) {
              // do nothing configuration
          }
      }
  
  }
  