AbstractIntervalTimer.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;

/**
 * {@code AbstractIntervalTimer} is common base class for {@link
 * Timer} implementations that base measure the change in some value
 * between the point where the timer is started and the point where
 * the timer is stopped.
 *
 * <p>This class is thread-safe.
 *
 */
public abstract class AbstractIntervalTimer implements Timer {
  // This object serves as its own lock protecting the following
  // fields.
  protected boolean running = false;
  protected long startTime = 0L;
  protected long cumulativeTime = 0L;

  @Override
  public synchronized void start() {
    if (running) {
      throw new IllegalStateException("already running");
    }

    startTime = getCurrent();
    running = true;
  }

  @Override
  public synchronized void stop() {
    if (!running) {
      throw new IllegalStateException("not running");
    }

    update(getCurrent());
    running = false;
  }

  @Override
  public synchronized void update() {
    update(getCurrent());
  }

  @Override
  public long getNanoseconds() {
    double ratio = getRatio();
    synchronized (this) {
      if (running) {
        return cumulativeTime + ((long) ((getCurrent() - startTime) * ratio));
      } else {
        return cumulativeTime;
      }
    }
  }

  /**
   * The fraction of the change in the underlying counter which will
   * be attributed to this timer.  By default, 100% of it.
   */
  protected double getRatio() {
    return 1.0;
  }

  protected void update(long currentValue) {
    synchronized (this) {
      long increment = (long) ((currentValue - startTime) * getRatio());
      cumulativeTime += increment;
      startTime = currentValue;
    }
  }

  protected abstract long getCurrent();
}