content: /**
   * 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.
   */
  package org.apache.aurora.common.util;
  
  import java.time.Instant;
  
  /**
   * An abstraction of the system clock.
   * @author John Sirois
   */
  public interface Clock {
    // TODO(zmanji): Consider replacing this with java.time.Clock
    /**
     * A clock that returns the the actual time reported by the system.
     */
    Clock SYSTEM_CLOCK = new Clock() {
      @Override public long nowMillis() {
        return System.currentTimeMillis();
      }
      @Override public long nowNanos() {
        return System.nanoTime();
      }
      @Override public void waitFor(long millis) throws InterruptedException {
        Thread.sleep(millis);
      }
      @Override public Instant nowInstant() {
        return Instant.now();
      }
    };
  
    /**
     * Returns the current time in milliseconds since the epoch.
     *
     * @return The current time in milliseconds since the epoch.
     * @see System#currentTimeMillis()
     */
    long nowMillis();
  
    /**
     * Returns the current time in nanoseconds. Should be used only for relative timing.
     * See {@code System.nanoTime()} for tips on using the value returned here.
     *
     * @return A measure of the current time in nanoseconds.
     * @see System#nanoTime()
     */
    long nowNanos();
  
    /**
     * Waits for the given amount of time to pass on this clock before returning.
     *
     * @param millis the amount of time to wait in milliseconds
     * @throws InterruptedException if this wait was interrupted
     */
    void waitFor(long millis) throws InterruptedException;
  
    /**
     * Returns the current time as an java.time.Instant.
     *
     * @return the Instant representing the current time.
     * @see Instant#now()
     */
    Instant nowInstant();
  }
  