001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.util;
019
020import java.util.concurrent.atomic.AtomicLong;
021import org.apache.yetus.audience.InterfaceAudience;
022
023/**
024 * An clock which will never return the same clock twice.
025 */
026@InterfaceAudience.Private
027public class NonRepeatedEnvironmentEdge implements EnvironmentEdge {
028
029  private final AtomicLong prevTime = new AtomicLong(0L);
030
031  @Override
032  public long currentTime() {
033    for (long current;;) {
034      current = System.currentTimeMillis();
035      long prev = prevTime.get();
036      if (current <= prev) {
037        current = prev + 1;
038      }
039      if (prevTime.compareAndSet(prev, current)) {
040        return current;
041      }
042    }
043  }
044}