TimeBucketCounter.java
/*
* 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.catalina.util;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.res.StringManager;
/**
* This class maintains a thread safe hash map that has timestamp-based buckets followed by a string for a key, and a
* counter for a value. each time the increment() method is called it adds the key if it does not exist, increments its
* value and returns it. a maintenance thread cleans up keys that are prefixed by previous timestamp buckets.
*/
public class TimeBucketCounter {
private static final Log log = LogFactory.getLog(TimeBucketCounter.class);
private static final StringManager sm = StringManager.getManager(TimeBucketCounter.class);
/**
* Map to hold the buckets
*/
private final ConcurrentHashMap<String,AtomicInteger> map = new ConcurrentHashMap<>();
/**
* Milliseconds bucket size as a Power of 2 for bit shift math, e.g. 16 for 65_536ms which is about 1:05 minute
*/
private final int numBits;
/**
* Ratio of actual duration to config duration
*/
private final double ratio;
/**
* The future allowing control of the background processor.
*/
private ScheduledFuture<?> maintenanceFuture;
private ScheduledFuture<?> monitorFuture;
private final ScheduledExecutorService executorService;
private final long sleeptime;
/**
* Creates a new TimeBucketCounter with the specified lifetime.
*
* @param bucketDuration duration in seconds, e.g. for 1 minute pass 60
* @param executorService the executor service which will be used to run the maintenance
*/
public TimeBucketCounter(int bucketDuration, ScheduledExecutorService executorService) {
this.executorService = executorService;
int durationMillis = bucketDuration * 1000;
int bits = 0;
int pof2 = nextPowerOf2(durationMillis);
int bitCheck = pof2;
while (bitCheck > 1) {
bitCheck = pof2 >> ++bits;
}
this.numBits = bits;
this.ratio = ratioToPowerOf2(durationMillis);
int cleanupsPerBucketDuration = (durationMillis >= 60_000) ? 6 : 3;
sleeptime = durationMillis / cleanupsPerBucketDuration;
// Start our thread
if (sleeptime > 0) {
monitorFuture = executorService
.scheduleWithFixedDelay(new MaintenanceMonitor(), 0, 60, TimeUnit.SECONDS);
}
}
/**
* Increments the counter for the passed identifier in the current time bucket and returns the new value.
*
* @param identifier an identifier for which we want to maintain count, e.g. IP Address
*
* @return the count within the current time bucket
*/
public final int increment(String identifier) {
String key = getCurrentBucketPrefix() + "-" + identifier;
AtomicInteger ai = map.computeIfAbsent(key, v -> new AtomicInteger());
return ai.incrementAndGet();
}
/**
* Calculates the current time bucket prefix by shifting bits for fast division, e.g. shift 16 bits is the same as
* dividing by 65,536 which is about 1:05m.
*
* @return The current bucket prefix.
*/
public final int getCurrentBucketPrefix() {
return (int) (System.currentTimeMillis() >> this.numBits);
}
public int getNumBits() {
return numBits;
}
/**
* The actual duration may differ from the configured duration because it is set to the next power of 2 value in
* order to perform very fast bit shift arithmetic.
*
* @return the actual bucket duration in milliseconds
*/
public int getActualDuration() {
return (int) Math.pow(2, getNumBits());
}
/**
* Returns the ratio between the configured duration param and the actual duration which will be set to the next
* power of 2. We then multiply the configured requests param by the same ratio in order to compensate for the added
* time, if any.
*
* @return the ratio, e.g. 1.092 if the actual duration is 65_536 for the configured duration of 60_000
*/
public double getRatio() {
return ratio;
}
/**
* Returns the ratio to the next power of 2 so that we can adjust the value.
*/
static double ratioToPowerOf2(int value) {
double nextPO2 = nextPowerOf2(value);
return Math.round((1000 * nextPO2 / value)) / 1000d;
}
/**
* Returns the next power of 2 given a value, e.g. 256 for 250, or 1024, for 1000.
*/
static int nextPowerOf2(int value) {
int valueOfHighestBit = Integer.highestOneBit(value);
if (valueOfHighestBit == value) {
return value;
}
return valueOfHighestBit << 1;
}
/**
* When we want to test a full bucket duration we need to sleep until the next bucket starts.
*
* @return the number of milliseconds until the next bucket
*/
public long getMillisUntilNextBucket() {
long millis = System.currentTimeMillis();
long nextTimeBucketMillis = ((millis + (long) Math.pow(2, numBits)) >> numBits) << numBits;
long delta = nextTimeBucketMillis - millis;
return delta;
}
/**
* Sets isRunning to false to terminate the maintenance thread.
*/
public void destroy() {
// Stop our thread
if (monitorFuture != null) {
monitorFuture.cancel(true);
monitorFuture = null;
}
if (maintenanceFuture != null) {
maintenanceFuture.cancel(true);
maintenanceFuture = null;
}
}
private class Maintenance implements Runnable {
@Override
public void run() {
String currentBucketPrefix = String.valueOf(getCurrentBucketPrefix());
ConcurrentHashMap.KeySetView<String,AtomicInteger> keys = map.keySet();
// remove obsolete keys
keys.removeIf(k -> !k.startsWith(currentBucketPrefix));
}
}
private class MaintenanceMonitor implements Runnable {
@Override
public void run() {
if (sleeptime > 0 &&
(maintenanceFuture == null || maintenanceFuture.isDone())) {
if (maintenanceFuture != null && maintenanceFuture.isDone()) {
// There was an error executing the scheduled task, get it and log it
try {
maintenanceFuture.get();
} catch (InterruptedException | ExecutionException e) {
log.error(sm.getString("timebucket.maintenance.error"), e);
}
}
maintenanceFuture = executorService.scheduleWithFixedDelay(new Maintenance(), sleeptime, sleeptime,
TimeUnit.MILLISECONDS);
}
}
}
}