Timer.java

/**
 * Copyright 2007 Google Inc. All Rights Reserved.
 * 
 * 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 com.google.apphosting.runtime.timer;

public interface Timer {
  /**
   * Start the timer running.
   *
   * @throws IllegalStateException If it was already running.
   */
  public void start();

  /**
   * Stop the timer.
   *
   * @throws IllegalStateException If it was not running.
   */
  public void stop();

  /**
   * Get the number of nanoseconds that elapsed between when the
   * {@code Timer} was started and when it was stopped.  Note that the
   * return value has nanosecond precision but not necessarily
   * nanosecond accuracy.
   */
  public long getNanoseconds();

  /**
   * Update any internal state.  For example, some {@link Timer}
   * implementations may take snapshots of data that may be
   * unavailable in the future.  Clients should call this method
   * periodically to qensure that any state is being updated.  For an
   * example, see {@link JmxThreadGroupCpuTimer#update}.
   */
  public void update();
}