ClockWithOffset.java

/**
 * Copyright 2014 Netflix, Inc.
 * <p/>
 * 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
 * <p/>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p/>
 * 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 com.netflix.servo.util;

/**
 * A {@link Clock} that provides a way to modify the time returned by
 * {@link System#currentTimeMillis()}.
 * <p/>
 * This can be used during application shutdown to force the clock forward and get the
 * latest values which normally
 * would not be returned until the next step boundary is crossed.
 */
public enum ClockWithOffset implements Clock {
  /**
   * Singleton.
   */
  INSTANCE;

  private volatile long offset = 0L;

  /**
   * Sets the offset for the clock.
   *
   * @param offset Number of milliseconds to add to the current time.
   */
  public void setOffset(long offset) {
    if (offset >= 0) {
      this.offset = offset;
    }
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public long now() {
    return offset + System.currentTimeMillis();
  }
}