BackoffSleeper.java

package org.skyscreamer.nevado.jms.util;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * This "sleeper" sleeps and backs off over time until it is reset.  It is used when looking for messages, so active
 * destinations can be checked more frequently for better response.  Less active destinations will be checked less
 * frequently as the sleeper backs off, to save AWS costs and unnecessary network calls.
 *
 * @author Carter Page <carter@skyscreamer.org>
 */
public class BackoffSleeper {
    private final Log _log = LogFactory.getLog(getClass());

    private volatile long _wait;
    private final long _minWait;
    private final long _maxWait;
    private final double _backoffMultiplier;
    private final Object _waiter = new Object();

    public BackoffSleeper(long minWait, long maxWait, double backoffMultiplier) {
        if (minWait <= 0)
        {
            throw new IllegalArgumentException("Minimum wait must be at least 1 ms");
        }
        if (maxWait <= minWait)
        {
            throw new IllegalArgumentException("Maximum wait must be greater than minimum wait");
        }
        if (backoffMultiplier <= 1.0)
        {
            throw new IllegalArgumentException("Backoff multiplier must be greater than 1.0");
        }
        _minWait = minWait;
        _maxWait = maxWait;
        _backoffMultiplier = backoffMultiplier;
        reset();
    }

    public void reset() {
        _wait = _minWait;
    }

    public void sleep() throws InterruptedException {
        synchronized (_waiter) {
            _waiter.wait(_wait);
        }
        if (_wait < _maxWait) {
            _wait = Math.round(_wait * _backoffMultiplier);
            if (_wait > _maxWait) {
                _wait = _maxWait;
            }
        }
    }

    public void stopSleeping() {
        synchronized (_waiter) {
            _waiter.notifyAll();
        }
    }
}