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/*
* Copyright 2006-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* 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 com.amazon.carbonado.util;
/**
* General purpose class for throttling work relative to its actual measured
* performance. To throttle a task, call the throttle method each time a unit
* of work has been performed. It computes a rolling average for the amount of
* time it takes to perform some work, and then it sleeps a calculated amount
* of time to throttle back.
*
* <p>Instances are intended for use by one thread, and so they are not
* thread-safe.
*
* @author Brian S O'Neill
*/
public class Throttle {
private final double[] mWorkTimeSamples;
// Next index in mSamples to use.
private int mSampleIndex;
private double mWorkTimeSum;
// Amount of samples gathered.
private int mSampleCount;
private long mLastTimestampNanos;
private double mSleepRequiredNanos;
/**
* @param windowSize amount of samples to keep in the rolling average
*/
public Throttle(int windowSize) {
if (windowSize < 1) {
throw new IllegalArgumentException();
}
mWorkTimeSamples = new double[windowSize];
}
/**
* @param desiredSpeed 1.0 = perform work at full speed,
* 0.5 = perform work at half speed, 0.0 = fully suspend work
* @param sleepPrecisionMillis sleep precision, in milliseconds. Typical
* value is 10 to 100 milliseconds.
*/
public void throttle(double desiredSpeed, long sleepPrecisionMillis)
throws InterruptedException
{
long timestampNanos = System.nanoTime();
int sampleCount = mSampleCount;
int index = mSampleIndex;
double workTime = timestampNanos - mLastTimestampNanos;
double workTimeSum = mWorkTimeSum + workTime;
double[] workTimeSamples = mWorkTimeSamples;
if (sampleCount >= workTimeSamples.length) {
workTimeSum -= workTimeSamples[index];
double average = workTimeSum / sampleCount;
double sleepTimeNanos = (average / desiredSpeed) - average;
double sleepRequiredNanos = mSleepRequiredNanos + sleepTimeNanos;
if (sleepRequiredNanos > 0.0) {
double sleepRequiredMillis = sleepRequiredNanos * (1.0 / 1000000);
long millis;
if (sleepRequiredMillis > Long.MAX_VALUE) {
millis = Long.MAX_VALUE;
} else {
millis = Math.max(sleepPrecisionMillis, (long) sleepRequiredMillis);
}
Thread.sleep(millis);
long nextNanos = System.nanoTime();
// Subtract off time spent in this method, including sleep.
sleepRequiredNanos -= (nextNanos - timestampNanos);
timestampNanos = nextNanos;
}
mSleepRequiredNanos = sleepRequiredNanos;
}
workTimeSamples[index] = workTime;
index++;
if (index >= workTimeSamples.length) {
index = 0;
}
mSampleIndex = index;
mWorkTimeSum = workTimeSum;
if (sampleCount < workTimeSamples.length) {
mSampleCount = sampleCount + 1;
}
mLastTimestampNanos = timestampNanos;
}
/**
* Test program which exercises the CPU in an infinite loop, throttled by
* the amount given in args[0]. On a machine performing no other work, the
* average CPU load should be about the same as the throttled speed.
*
* @param args args[0] - desired speed, 0.0 to 1.0
*/
public static void main(String[] args) throws Exception {
Throttle t = new Throttle(50);
double desiredSpeed = Double.parseDouble(args[0]);
while (true) {
new java.util.Date().toString();
t.throttle(desiredSpeed, 100);
}
}
}
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