ptlrs commented on code in PR #8498: URL: https://github.com/apache/ozone/pull/8498#discussion_r2212061545
########## hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/utils/SlidingWindow.java: ########## @@ -0,0 +1,133 @@ +/* + * 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.hadoop.ozone.container.common.utils; + +import java.time.Clock; +import java.time.Duration; +import java.util.ArrayDeque; +import java.util.Deque; +import org.apache.hadoop.util.Time; + +/** + * A time-based sliding window implementation that tracks event timestamps. + */ +public class SlidingWindow { + private final Object lock = new Object(); + private final int windowSize; + private final Deque<Long> timestamps; + private final long expiryDurationMillis; + private final Clock clock; + + /** + * Default constructor that uses system clock. + * + * @param windowSize the maximum number of events that are tracked + * @param expiryDuration the duration after which an entry in the window expires + */ + public SlidingWindow(int windowSize, Duration expiryDuration) { + this(windowSize, expiryDuration, new SystemClock()); + } + + /** + * Constructor with custom clock for testing. + * + * @param windowSize the maximum number of events that are tracked + * @param expiryDuration the duration after which an entry in the window expires + * @param clock the clock to use for time measurements + */ + public SlidingWindow(int windowSize, Duration expiryDuration, Clock clock) { + if (windowSize <= 0) { + throw new IllegalArgumentException("Window size must be greater than 0"); + } + if (expiryDuration.isNegative() || expiryDuration.isZero()) { + throw new IllegalArgumentException("Expiry duration must be greater than 0"); + } + this.windowSize = windowSize; + this.expiryDurationMillis = expiryDuration.toMillis(); + this.clock = clock; + // We limit the initial queue size to 100 to control the memory usage + this.timestamps = new ArrayDeque<>(Math.min(windowSize + 1, 100)); + } + + public void add() { + synchronized (lock) { + if (isFull()) { + timestamps.remove(); + } + + timestamps.add(getCurrentTime()); + } + } + + /** + * Checks if the sliding window has exceeded its maximum size. + * This is useful to track if we have encountered more events than the window's defined limit. + * @return true if the number of tracked timestamps in the sliding window + * exceeds the specified window size, false otherwise. + */ + public boolean isFull() { + synchronized (lock) { + removeExpired(); + return timestamps.size() > windowSize; Review Comment: The exceeded `(> window size)` case is the intention of this method. We want to find if more events than the tolerable amount have occurred. Consider the volume scanner use case where we want to tolerate 5 failures over a time period. What should happen if we receive 6 events within a valid time period? We don't want to remove the oldest element and add the 6th one as we will lose the information which illustrates that more failures than the tolerated amount have occurred. The other option is to have the caller create the window size of (toleration + 1) and the `isFull` method checks for `(== window size)`. I think setting the window size in this manner is not intuitive for the caller. -- 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: issues-unsubscr...@ozone.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@ozone.apache.org For additional commands, e-mail: issues-h...@ozone.apache.org
