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.yarn.util;
019
020import org.apache.hadoop.classification.InterfaceAudience.Public;
021import org.apache.hadoop.classification.InterfaceStability.Evolving;
022import org.apache.hadoop.util.Time;
023
024/**
025 * A monotonic clock from some arbitrary time base in the past, counting in
026 * milliseconds, and not affected by settimeofday or similar system clock
027 * changes.
028 * This is appropriate to use when computing how much longer to wait for an
029 * interval to expire.
030 * This function can return a negative value and it must be handled correctly
031 * by callers. See the documentation of System#nanoTime for caveats.
032 */
033@Public
034@Evolving
035public class MonotonicClock implements Clock {
036
037  /**
038   * Get current time from some arbitrary time base in the past, counting in
039   * milliseconds, and not affected by settimeofday or similar system clock
040   * changes.
041   * @return a monotonic clock that counts in milliseconds.
042   */
043  public long getTime() {
044    return Time.monotonicNow();
045  }
046}