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/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.qpid.junit.extensions;
/**
* BatchedThrottle is a {@link SleepThrottle} that uses batching to achieve much higher throttling rates than a sleep
* throttle can. Sleep throttle has difficulties once the rate gets above a few hundred hertz, because the JVM cannot
* generate timed pauses that are that short. BatchedThrottle gets around this by only inserting pauses once every so
* many calls to the {@link #throttle()} method, and using a sleep throttle run at a lower rate. The rate for the sleep
* throttle is chosen so that it remains under 100hz. The final throttling rate of this throttle is equal to the batch
* size times the rate of the underlying sleep throttle.
*
* <p/>The batching calculation involves taking the log to the base 100 of the desired rate and rounding this to
* an integer. The batch size is always an exact power of 100 because of the rounding. The rate for an underlying
* sleep throttle is then chosen appropriately.
*
* <p/>In practice, the accuracy of a BacthedThrottle skews off but can sometimes even be reasonable up to ten thousand
* hertz compared with 100 Hz for a {@link SleepThrottle}.
*
* <p><table id="crc"><caption>CRC Card</caption>
* <tr><th> Responsibilities <th> Collaborations
* <tr><td> Accept throttling rate in operations per second.
* <tr><td> Inject short pauses, occasionaly, to fill out processing cycles to a specified rate.
* <tr><td> Check against a throttle speed without waiting.
* </table>
*
* @todo Should always round the log base 100 down to the nearest integer?
*
* @author Rupert Smith
*/
public class BatchedThrottle extends BaseThrottle
{
/** Holds the batch size. */
int batchSize;
/** The call count within the current batch. */
long callCount;
/** Holds a sleep throttle configured to run at the batched rate. */
private Throttle batchRateThrottle = new SleepThrottle();
/**
* Specifies the throttling rate in operations per second.
*
* @param hertz The throttling rate in cycles per second.
*/
public void setRate(float hertz)
{
// Pass the rate unaltered down to the base implementation, for the check method.
super.setRate(hertz);
// Log base 10 over 2 is used here to get a feel for what power of 100 the total rate is.
// As the total rate goes up the powers of 100 the batch size goes up by powers of 100 to keep the
// throttle rate in the range 1 to 100.
int x = (int) (Math.log10(hertz) / 2);
batchSize = (int) Math.pow(100, x);
float throttleRate = hertz / batchSize;
// Reset the call count.
callCount = 0;
// Set the sleep throttle wrapped implementation at a rate within its abilities.
batchRateThrottle.setRate(throttleRate);
}
/**
* Throttle calls to this method to the rate specified by the {@link #setRate(float)} method.
*/
public void throttle()
{
if ((callCount++ % batchSize) == 0)
{
batchRateThrottle.throttle();
}
}
}
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