package com.bigdata.util.concurrent;
import java.util.concurrent.Callable;
import org.apache.log4j.Logger;
/**
* Class tracks a the moving average of some sampled datum.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class MovingAverageTask implements Runnable {
protected static final Logger log = Logger
.getLogger(MovingAverageTask.class);
/**
* The label used in log messages.
*/
protected final String name;
/**
* Used to sample whatever is being measured.
*/
protected final Callable<?extends Number> sampleTask;
/**
* The weight used to compute the moving average.
*/
protected final double w;
/**
* #of samples taken so far.
*/
protected long nsamples = 0;
/**
* The moving average.
*/
protected double average = 0d;
/**
* The current value of the moving average.
*/
public double getMovingAverage() {
return average;
}
// /**
// * Scaling factor converts nanoseconds to milliseconds.
// */
// static protected final double scalingFactor = 1d / TimeUnit.NANOSECONDS
// .convert(1, TimeUnit.MILLISECONDS);
/**
* The weight used to compute the moving average.
*/
public double getWeight() {
return w;
}
/**
* #of samples taken so far.
*/
public long getSampleCount() {
return nsamples;
}
/**
* The recommended default weight.
*/
public static final double DEFAULT_WEIGHT = .2d;
/**
*
* @param name
* The label for log messages.
* @param sampleTask
* Task that returns a sampled value.
*/
public MovingAverageTask(final String name,
final Callable<? extends Number> sampleTask) {
this(name, sampleTask, DEFAULT_WEIGHT);
}
/**
* Core impl.
*
* @param name
* The label for log messages.
* @param queue
* Task that returns a sampled value.
* @param w
* The weight to be used by
* {@link #getMovingAverage(double, double, double)}
*/
public MovingAverageTask(final String name,
final Callable<? extends Number> sampleTask, final double w) {
if (name == null)
throw new IllegalArgumentException();
if (sampleTask == null)
throw new IllegalArgumentException();
if (w <= 0d || w >= 1d)
throw new IllegalArgumentException();
this.name = name;
this.sampleTask = sampleTask;
this.w = w;
}
/**
* Compute a moving average: <code>(1 - w) * avg + w * q</code>
*
* @param avg
* The previous average and initially zero (0.0).
* @param q
* The current value (e.g., the instantaneous measurement of the
* #of active tasks plus the length of the queue).
* @param w
* The weight for the moving average in (0:1). Values around .2
* seem appropriate.
*
* @return The updated moving average.
*/
final static protected double getMovingAverage(final double avg,
final double q, final double w) {
return (1 - w) * avg + (w * q);
}
/**
* Note: don't throw anything from here or it will cause the task to no
* longer be run!
*/
public void run() {
try {
final double sample = sampleTask.call().doubleValue();
average = getMovingAverage(average, sample, w);
nsamples++;
} catch (Exception ex) {
log.warn(name, ex);
}
}
}