geode-core/src/main/java/org/apache/geode/management/internal/beans/SequenceNumber.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.geode.management.internal.beans;

import java.util.concurrent.atomic.AtomicLong;

import org.apache.geode.annotations.internal.MakeNotStatic;

/**
 * Class to give a consistent sequence number to notifications
 *
 *
 */
public class SequenceNumber {

  /** Sequence number for resource related notifications **/
  @MakeNotStatic
  private static final AtomicLong sequenceNumber = new AtomicLong(1);

  public static long next() {
    long retVal = sequenceNumber.incrementAndGet();

    if (retVal == Long.MAX_VALUE || retVal < 0) {// retVal <0 is checked for cases where other
                                                 // threads might have incremented sequenceNumber
                                                 // beyond Long.MAX_VALUE

      synchronized (SequenceNumber.class) {
        long currentValue = sequenceNumber.get();
        if (currentValue == Long.MAX_VALUE || retVal < 0) {
          sequenceNumber.set(1);
          retVal = sequenceNumber.get();
        } else {
          retVal = currentValue;
        }
      }
    }
    return retVal;
  }

}