isapir commented on code in PR #607: URL: https://github.com/apache/tomcat/pull/607#discussion_r1153771643
########## java/org/apache/catalina/util/TimeBucketCounter.java: ########## @@ -0,0 +1,217 @@ +/* + * 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.atomic.AtomicInteger; + +/** + * 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 { + + /** + * 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; + + /** + * flag for the maintenance thread + */ + volatile boolean isRunning = false; + + /** + * + * @param bucketDuration duration in seconds, e.g. for 1 minute pass 60 + */ + public TimeBucketCounter(int bucketDuration) { + + 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; + Thread mt = new MaintenanceThread(durationMillis / cleanupsPerBucketDuration); + mt.start(); + } + + /** + * 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 + */ + public final int getCurrentBucketPrefix() { + return (int) (System.currentTimeMillis() >> this.numBits); + } + + /** + * + * @return + */ + 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 + * + * @param value + * @return + */ + 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 + * + * @param value + * @return + */ + 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() { + this.isRunning = false; + } + + /** + * this class runs a background thread to clean up old keys from the map + */ + class MaintenanceThread extends Thread { + + final long sleeptime; + + public MaintenanceThread(long sleeptime) { + super.setDaemon(true); + this.sleeptime = sleeptime; + } + + @Override + public void start() { + isRunning = true; + super.start(); + } + + @Override + public void run() { + + while (isRunning) { + String currentBucketPrefix = String.valueOf(getCurrentBucketPrefix()); + ConcurrentHashMap.KeySetView<String, AtomicInteger> keys = map.keySet(); + + for (String k : keys) { + if (!k.startsWith(currentBucketPrefix)) { + // the key is obsolete, remove it + keys.remove((k)); + } + } Review Comment: Looks like Collection.removeIf() has been added in Java 8 [1]. The code also makes use of Map.computeIfAbsent() which was also add in Java 8. Since Tomcat 8.5 EOL is exactly a year from now [2], we need to decide whether we should port this back to 8.5. The main question that I have to Tomcat 8.5 users is: what's holding you back from upgrading to Tomcat 9.0? [1] https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html#removeIf-java.util.function.Predicate- [2] https://tomcat.apache.org/tomcat-85-eol.html -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
