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/*
* 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.HashSet;
import java.util.Set;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.zookeeper.common.Time;
import org.apache.zookeeper.server.RateLogger;
import org.apache.zookeeper.server.ServerMetrics;
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 Object processingCompletedEvent = new Object();
private final WorkerService cleaners;
private final Set<Integer> deadWatchers;
private final IDeadWatcherListener listener;
private final int watcherCleanThreshold;
private final int watcherCleanIntervalInSeconds;
private final int maxInProcessingDeadWatchers;
private final AtomicInteger totalDeadWatchers = new AtomicInteger();
public WatcherCleaner(IDeadWatcherListener 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(IDeadWatcherListener 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<>();
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) {
try {
RATE_LOGGER.rateLimitLog("Waiting for dead watchers cleaning");
long startTime = Time.currentElapsedTime();
synchronized (processingCompletedEvent) {
processingCompletedEvent.wait(100);
}
long latency = Time.currentElapsedTime() - startTime;
ServerMetrics.getMetrics().ADD_DEAD_WATCHER_STALL_TIME.add(latency);
} catch (InterruptedException e) {
LOG.info("Got interrupted while waiting for dead watches queue size");
break;
}
}
synchronized (this) {
if (deadWatchers.add(watcherBit)) {
totalDeadWatchers.incrementAndGet();
ServerMetrics.getMetrics().DEAD_WATCHERS_QUEUED.add(1);
if (deadWatchers.size() >= watcherCleanThreshold) {
synchronized (cleanEvent) {
cleanEvent.notifyAll();
}
}
}
}
}
@Override
public void run() {
while (!stopped) {
synchronized (cleanEvent) {
try {
// add some jitter to avoid cleaning dead watchers at the
// same time in the quorum
if (!stopped && deadWatchers.size() < watcherCleanThreshold) {
int maxWaitMs = (watcherCleanIntervalInSeconds
+ ThreadLocalRandom.current().nextInt(watcherCleanIntervalInSeconds / 2 + 1)) * 1000;
cleanEvent.wait(maxWaitMs);
}
} catch (InterruptedException e) {
LOG.info("Received InterruptedException while waiting for cleanEvent");
break;
}
}
if (deadWatchers.isEmpty()) {
continue;
}
synchronized (this) {
// Clean the dead watchers need to go through all the current
// watches, which is pretty heavy and may take a second if
// there are millions of watches, that's why we're doing lazily
// batch clean up in a separate thread with a snapshot of the
// current dead watchers.
final Set<Integer> snapshot = new HashSet<>(deadWatchers);
deadWatchers.clear();
int total = snapshot.size();
LOG.info("Processing {} dead watchers", total);
cleaners.schedule(new WorkRequest() {
@Override
public void doWork() throws Exception {
long startTime = Time.currentElapsedTime();
listener.processDeadWatchers(snapshot);
long latency = Time.currentElapsedTime() - startTime;
LOG.info("Takes {} to process {} watches", latency, total);
ServerMetrics.getMetrics().DEAD_WATCHERS_CLEANER_LATENCY.add(latency);
ServerMetrics.getMetrics().DEAD_WATCHERS_CLEARED.add(total);
totalDeadWatchers.addAndGet(-total);
synchronized (processingCompletedEvent) {
processingCompletedEvent.notifyAll();
}
}
});
}
}
LOG.info("WatcherCleaner thread exited");
}
public void shutdown() {
stopped = true;
deadWatchers.clear();
cleaners.stop();
this.interrupt();
if (LOG.isInfoEnabled()) {
LOG.info("WatcherCleaner thread shutdown is initiated");
}
}
}
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