/* Copyright (c) 2006-2009 Jan S. Rellermeyer
* Systems Group,
* Department of Computer Science, ETH Zurich.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* - Neither the name of ETH Zurich nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
package ch.ethz.iks.r_osgi.impl;
import ch.ethz.iks.r_osgi.types.Timestamp;
import ch.ethz.iks.util.MathUtils;
/**
* <p>
* Encapsulates an offset that a remote peer's clock has.
* </p>
* <p>
* Used to transform <code>Timestamp</code> objects received from remote peers
* to local time.
* </p>
*
* @author Jan S. Rellermeyer, ETH Z�rich.
* @since 0.2
*/
final class TimeOffset {
/**
* the offset.
*/
private long offset;
/**
* the last update time.
*/
private long lastUpdate;
/**
* the lifetime of this offset.
*/
private int lifetime;
/**
* the length of the next series.
*/
private int seriesLength;
/**
* the initial lifetime in minutes.
*/
private static final int INITIAL_LIFETIME = 1;
/**
* the maximum lifetime.
*/
private static final int MAX_LIFETIME = 10;
/**
* the minimum lifetime.
*/
private static final int MIN_LIFETIME = 1;
/**
* the default series length.
*/
private static final int DEFAULT_SERIES = 8;
/**
* the maximum series length.
*/
private static final int MAX_SERIES = 32;
/**
* the minimum series length.
*/
private static final int MIN_SERIES = 4;
/**
* creates a new TimeOffset object.
*
* @param timeSerie
* a series of time measurements.
*/
TimeOffset(final long[] timeSerie) {
// initially redo after half a minute
lifetime = INITIAL_LIFETIME;
seriesLength = DEFAULT_SERIES;
update(timeSerie);
}
/**
* update the offset with a new series.
*
* @param timeSeries
* the series.
*/
void update(final long[] timeSeries) {
final int len = timeSeries.length / 2;
final long[] offsets = new long[len];
long l = 0;
long h = 0;
for (int i = 0; i < len; i++) {
final long local = timeSeries[2 * i];
final long remote = timeSeries[2 * i + 1];
offsets[i] = local - remote;
l = l + MathUtils.lower32(offsets[i]);
h = h + MathUtils.higher32(offsets[i]);
}
final int shift = MathUtils.log2(len);
l = l >>> shift;
h = h << (32 - shift);
final long mean = (h | l);
if (lastUpdate != 0) {
// heuristic adaptation of seriesLength
final long stddev = (MathUtils.max(offsets) - MathUtils
.min(offsets)) / 3;
/*
* System.out.println("STDDEV " + stddev);
*/
if (stddev < 10) {
seriesLength /= 2;
}
if (stddev > 40) {
seriesLength *= 2;
}
if (stddev > 100) {
seriesLength *= 2;
}
// heuristic adaptation of lifetime
final long diff = MathUtils.abs(offset - mean);
/*
* System.out.println("DIFF " + diff);
*/
if (diff < (50 - 0.5 * (lifetime * lifetime))) {
lifetime++;
}
if (diff > 100) {
lifetime--;
}
if (diff > 500) {
lifetime -= 4;
}
if (seriesLength > MAX_SERIES) {
seriesLength = MAX_SERIES;
}
if (seriesLength < MIN_SERIES) {
seriesLength = MIN_SERIES;
}
if (lifetime > MAX_LIFETIME) {
lifetime = MAX_LIFETIME;
}
if (lifetime < MIN_LIFETIME) {
lifetime = MIN_LIFETIME;
}
}
lastUpdate = System.currentTimeMillis();
offset = mean;
}
/**
* has this time offset expired ?
*
* @return <code>true</code> if expired, <code>false</code> otherwise.
*/
boolean isExpired() {
return (System.currentTimeMillis() - lastUpdate > lifetime * 60000L);
}
/**
* the length of the series. Note that this value is <i>i</i> = <i>2 * n</i>
* or in other words two times the number of rounds.
*
* @return the length of the series.
*/
int seriesLength() {
return seriesLength;
}
/**
* transform a remote timestamp.
*
* @param remoteTimestamp
* the remote timestamp.
* @return the timestamp transformed into local time.
*/
Long transform(final Long remoteTimestamp) {
return new Long(remoteTimestamp.longValue() + offset);
}
/**
* transform a timestamp.
*
* @param timestamp
* the timestamp.
* @return the transformed timestamp.
*/
Timestamp transform(final Timestamp timestamp) {
return Timestamp.from((timestamp.getValue() + 1000 * offset));
}
}