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Ehcache is an open source, standards-based cache used to boost performance, offload the database and simplify scalability. Ehcache is robust, proven and full-featured and this has made it the most widely-used Java-based cache.

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/**
 *  Copyright Terracotta, Inc.
 *
 *  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 net.sf.ehcache.statistics.extended;

import java.util.List;
import java.util.concurrent.ScheduledExecutorService;

import org.terracotta.statistics.Time;
import org.terracotta.statistics.ValueStatistic;
import org.terracotta.statistics.archive.Timestamped;

/**
 * Statistic implementation that stops sampling history if the last history access is 
 * before a user supplied timestamp.
 * 
 * @param  statistic type
 * @author Chris Dennis
 */
public class SemiExpiringStatistic extends AbstractStatistic {
  
    /** The active. */
    private boolean active = false;

    /** The touch timestamp. */
    private long touchTimestamp = -1;

    /**
     * Creates a new semi-expiring statistic.
     * 
     * @param source statistic source
     * @param executor executor to use for sampling
     * @param historySize size of sample history
     * @param historyNanos period between samples
     */
    public SemiExpiringStatistic(ValueStatistic source, ScheduledExecutorService executor, int historySize, long historyNanos) {
        super(source, executor, historySize, historyNanos);
    }

    @Override
    public List> history() {
        touch();
        return super.history();
    }
    
    /*
     * (non-Javadoc)
     *
     * @see net.sf.ehcache.statisticsV2.extended.ExtendedStatistics.Statistic#active()
     */
    @Override
    public final synchronized boolean active() {
        return active;
    }

    /**
     * Touch.
     */
    protected final synchronized void touch() {
        touchTimestamp = Time.absoluteTime();
        start();
    }

    /**
     * Start.
     */
    protected final synchronized void start() {
        if (!active) {
            startStatistic();
            startSampling();
            active = true;
        }
    }

    /**
     * Expire.
     *
     * @param expiry the expiry
     * @return true, if successful
     */
    protected final synchronized boolean expire(long expiry) {
        if (touchTimestamp < expiry) {
            if (active) {
                stopSampling();
                stopStatistic();
                active = false;
            }
            return true;
        } else {
            return false;
        }
    }

    /**
     * Stop statistic.
     */
    protected void stopStatistic() {
      //no-op
    }

    /**
     * Start statistic.
     */
    protected void startStatistic() {
      //no-op
    }
}