content: /*
   * 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.beam.sdk.util;
  
  /**
   * Nano clock which can be used to measure elapsed time in nanoseconds.
   *
   * <p>The default system implementation can be accessed at {@link #SYSTEM}. Alternative
   * implementations may be used for testing.
   */
  @FunctionalInterface
  interface NanoClock {
  
    /**
     * Returns the current value of the most precise available system timer, in nanoseconds for use to
     * measure elapsed time, to match the behavior of {@link System#nanoTime()}.
     */
    long nanoTime();
  
    /**
     * Provides the default System implementation of a nano clock by using {@link System#nanoTime()}.
     */
    NanoClock SYSTEM = System::nanoTime;
  }
  