Github user hanm commented on a diff in the pull request: https://github.com/apache/zookeeper/pull/590#discussion_r220055291 --- Diff: src/java/main/org/apache/zookeeper/server/watch/WatcherCleaner.java --- @@ -0,0 +1,176 @@ +/** + * 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.zookeeper.server.watch; + +import java.util.Set; +import java.util.HashSet; +import java.util.Random; +import java.util.concurrent.atomic.AtomicInteger; + +import org.apache.zookeeper.common.Time; +import org.apache.zookeeper.server.RateLogger; +import org.apache.zookeeper.server.WorkerService; +import org.apache.zookeeper.server.WorkerService.WorkRequest; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Thread used to lazily clean up the closed watcher, it will trigger the + * clean up when the dead watchers get certain number or some number of + * seconds has elapsed since last clean up. + * + * Cost of running it: + * + * - need to go through all the paths even if the watcher may only + * watching a single path + * - block in the path BitHashSet when we try to check the dead watcher + * which won't block other stuff + */ +public class WatcherCleaner extends Thread { + + private static final Logger LOG = LoggerFactory.getLogger(WatcherCleaner.class); + private final RateLogger RATE_LOGGER = new RateLogger(LOG); + + private volatile boolean stopped = false; + private final Object cleanEvent = new Object(); + private final Random r = new Random(System.nanoTime()); + private final WorkerService cleaners; + + private final Set<Integer> deadWatchers; + private final DeadWatcherListener listener; + private final int watcherCleanThreshold; + private final int watcherCleanIntervalInSeconds; + private final int maxInProcessingDeadWatchers; + private final AtomicInteger totalDeadWatchers = new AtomicInteger(); + + public WatcherCleaner(DeadWatcherListener listener) { + this(listener, + Integer.getInteger("zookeeper.watcherCleanThreshold", 1000), + Integer.getInteger("zookeeper.watcherCleanIntervalInSeconds", 600), + Integer.getInteger("zookeeper.watcherCleanThreadsNum", 2), + Integer.getInteger("zookeeper.maxInProcessingDeadWatchers", -1)); + } + + public WatcherCleaner(DeadWatcherListener listener, + int watcherCleanThreshold, int watcherCleanIntervalInSeconds, + int watcherCleanThreadsNum, int maxInProcessingDeadWatchers) { + this.listener = listener; + this.watcherCleanThreshold = watcherCleanThreshold; + this.watcherCleanIntervalInSeconds = watcherCleanIntervalInSeconds; + int suggestedMaxInProcessingThreshold = + watcherCleanThreshold * watcherCleanThreadsNum; + if (maxInProcessingDeadWatchers > 0 && + maxInProcessingDeadWatchers < suggestedMaxInProcessingThreshold) { + maxInProcessingDeadWatchers = suggestedMaxInProcessingThreshold; + LOG.info("The maxInProcessingDeadWatchers config is smaller " + + "than the suggested one, change it to use {}", + maxInProcessingDeadWatchers); + } + this.maxInProcessingDeadWatchers = maxInProcessingDeadWatchers; + this.deadWatchers = new HashSet<Integer>(); + this.cleaners = new WorkerService("DeadWatcherCleanner", + watcherCleanThreadsNum, false); + + LOG.info("watcherCleanThreshold={}, watcherCleanIntervalInSeconds={}" + + ", watcherCleanThreadsNum={}, maxInProcessingDeadWatchers={}", + watcherCleanThreshold, watcherCleanIntervalInSeconds, + watcherCleanThreadsNum, maxInProcessingDeadWatchers); + } + + public void addDeadWatcher(int watcherBit) { + // Wait if there are too many watchers waiting to be closed, + // this is will slow down the socket packet processing and + // the adding watches in the ZK pipeline. + while (maxInProcessingDeadWatchers > 0 && !stopped && + totalDeadWatchers.get() >= maxInProcessingDeadWatchers) { --- End diff -- oops, did not see `maxInProcessingDeadWatchers > 0`. we are good here.
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