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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.util.counter.sampled;

import java.util.TimerTask;

import net.sf.ehcache.util.CircularLossyQueue;
import net.sf.ehcache.util.counter.CounterImpl;

/**
 * An implementation of {@link SampledCounter}
 *
 * @author Abhishek Sanoujam
 * @since 1.7
 *
 */
public class SampledCounterImpl extends CounterImpl implements SampledCounter {
    private static final int MILLIS_PER_SEC = 1000;

    /**
     * The history of this counter
     */
    protected final CircularLossyQueue history;

    /**
     * Should the counter reset on each sample?
     */
    protected final boolean resetOnSample;
    private final TimerTask samplerTask;
    private final long intervalMillis;

    /**
     * todo GL how many threads is this creating?
     * Constructor accepting a {@link SampledCounterConfig}
     *
     * @param config
     */
    public SampledCounterImpl(SampledCounterConfig config) {
        this(config.getIntervalSecs(), config.getHistorySize(), config.isResetOnSample(), config.getInitialValue(), true);
    }

    /**
     * Constructor accepting raw config values.
     *
     * @param intervalInSeconds sampling interval in seconds
     * @param historySize size of history sample
     * @param resetOnSample true to reset value on sample
     * @param initValue initial value
     * @param sampleNow true to record smaple immediately
     */
    public SampledCounterImpl(long intervalInSeconds, int historySize, boolean resetOnSample, long initValue, boolean sampleNow) {
        super(initValue);

        this.intervalMillis = intervalInSeconds * MILLIS_PER_SEC;
        this.history = new CircularLossyQueue(historySize);
        this.resetOnSample = resetOnSample;

        this.samplerTask = new TimerTask() {
            @Override
            public void run() {
                recordSample();
            }
        };

        if (sampleNow) {
            recordSample();
        }
    }

    /**
     * {@inheritDoc}
     */
    public TimeStampedCounterValue getMostRecentSample() {
        return this.history.peek();
    }

    /**
     * {@inheritDoc}
     */
    public TimeStampedCounterValue[] getAllSampleValues() {
        return this.history.toArray(new TimeStampedCounterValue[this.history.depth()]);
    }

    /**
     * {@inheritDoc}
     */
    public void shutdown() {
        if (samplerTask != null) {
            samplerTask.cancel();
        }
    }

    /**
     * Returns the timer task for this sampled counter
     *
     * @return the timer task for this sampled counter
     */
    public TimerTask getTimerTask() {
        return this.samplerTask;
    }

    /**
     * Returns the sampling thread interval in millis
     *
     * @return the sampling thread interval in millis
     */
    public long getIntervalMillis() {
        return intervalMillis;
    }

    /**
     * {@inheritDoc}
     */
    void recordSample() {
        final long sample;
        if (resetOnSample) {
            sample = getAndReset();
        } else {
            sample = getValue();
        }

        final long now = System.currentTimeMillis();
        TimeStampedCounterValue timedSample = new TimeStampedCounterValue(now, sample);

        history.push(timedSample);
    }

    /**
     * {@inheritDoc}
     */
    public long getAndReset() {
        return getAndSet(0L);
    }
}