GGraziadei commented on code in PR #8586: URL: https://github.com/apache/storm/pull/8586#discussion_r3209376086
########## storm-client/src/jvm/org/apache/storm/metrics2/EwmaGauge.java: ########## @@ -0,0 +1,89 @@ +/* + * 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 + * <p> + * http://www.apache.org/licenses/LICENSE-2.0 + * <p> + * 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.storm.metrics2; + +import static org.apache.storm.utils.ConfigUtils.RFC1889_ALPHA; + +import com.codahale.metrics.Gauge; + +import java.util.concurrent.atomic.AtomicLong; + +/** + * Lock-free jitter estimator following RFC 1889 Section 6.3.1. + * The jitter accumulator is stored as raw IEEE 754 bits in an AtomicLong + * so that CAS can be used without locks. + * Thread safety: addValue is lock-free; getValue is wait-free. + */ +public class EwmaGauge implements Gauge<Double> { + + private static final long UNSEEDED = Long.MIN_VALUE; + private static final long ZERO_BITS = Double.doubleToLongBits(0.0); + + private final AtomicLong lastTransit = new AtomicLong(UNSEEDED); + private final AtomicLong jitterBits = new AtomicLong(ZERO_BITS); + private final double alpha; + + EwmaGauge(double alpha) { + if (alpha <= 0.0 || alpha >= 1.0 || Double.isNaN(alpha)) { + throw new IllegalArgumentException( + "alpha must be in (0, 1), got: " + alpha); + } + this.alpha = alpha; + } + + EwmaGauge() { + this(RFC1889_ALPHA); // 1.0 / 16.0 + } + + /** + * Update the jitter estimate. + * + * @param transitMs transit time for this tuple: {@code arrival - timestamp} + * Negative values are silently ignored. + */ + public void addValue(long transitMs) { + if (transitMs < 0) { + return; + } + + // Seed on the very first packet: store transit, nothing to diff against yet. + if (lastTransit.compareAndSet(UNSEEDED, transitMs)) { + return; + } + + long prev = lastTransit.getAndSet(transitMs); + if (prev == UNSEEDED) { + // Lost a race during seeding; prev is not a real transit value. + return; + } + + double d = Math.abs(transitMs - prev); Review Comment: Thank you for the explanation, I forgot about the CA2 pathology for Math.abs(Long.MIN_VALUE) -- 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: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
