/**
* 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 com.twitter.distributedlog.zk;
import org.apache.bookkeeper.stats.Gauge;
import org.apache.bookkeeper.stats.StatsLogger;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Watcher Manager to manage watchers.
* <h3>Metrics</h3>
* <ul>
* <li> `total_watches`: total number of watches that managed by this watcher manager.
* <li> `num_child_watches`: number of paths that are watched for children changes by this watcher manager.
* </ul>
*/
public class ZKWatcherManager implements Watcher {
static final Logger logger = LoggerFactory.getLogger(ZKWatcherManager.class);
public static Builder newBuilder() {
return new Builder();
}
public static class Builder {
private String _name;
private StatsLogger _statsLogger;
public Builder name(String name) {
this._name = name;
return this;
}
public Builder statsLogger(StatsLogger statsLogger) {
this._statsLogger = statsLogger;
return this;
}
public ZKWatcherManager build() {
return new ZKWatcherManager(_name, _statsLogger);
}
}
private final String name;
private final StatsLogger statsLogger;
protected final ConcurrentMap<String, Set<Watcher>> childWatches;
protected final AtomicInteger allWatchesGauge;
private ZKWatcherManager(String name,
StatsLogger statsLogger) {
this.name = name;
this.statsLogger = statsLogger;
// watches
this.childWatches = new ConcurrentHashMap<String, Set<Watcher>>();
this.allWatchesGauge = new AtomicInteger(0);
// stats
this.statsLogger.registerGauge("total_watches", new Gauge<Number>() {
@Override
public Number getDefaultValue() {
return 0;
}
@Override
public Number getSample() {
return allWatchesGauge.get();
}
});
this.statsLogger.registerGauge("num_child_watches", new Gauge<Number>() {
@Override
public Number getDefaultValue() {
return 0;
}
@Override
public Number getSample() {
return childWatches.size();
}
});
}
public Watcher registerChildWatcher(String path, Watcher watcher) {
Set<Watcher> watchers = childWatches.get(path);
if (null == watchers) {
Set<Watcher> newWatchers = new HashSet<Watcher>();
Set<Watcher> oldWatchers = childWatches.putIfAbsent(path, newWatchers);
watchers = (null == oldWatchers) ? newWatchers : oldWatchers;
}
synchronized (watchers) {
if (childWatches.get(path) == watchers) {
if (watchers.add(watcher)) {
allWatchesGauge.incrementAndGet();
}
} else {
logger.warn("Watcher set for path {} has been changed while registering child watcher {}.",
path, watcher);
}
}
return this;
}
public void unregisterChildWatcher(String path, Watcher watcher) {
Set<Watcher> watchers = childWatches.get(path);
if (null == watchers) {
logger.warn("No watchers found on path {} while unregistering child watcher {}.",
path, watcher);
return;
}
synchronized (watchers) {
if (watchers.remove(watcher)) {
allWatchesGauge.decrementAndGet();
} else {
logger.warn("Remove a non-registered child watcher {} from path {}", watcher, path);
}
if (watchers.isEmpty()) {
childWatches.remove(path, watchers);
}
}
}
@Override
public void process(WatchedEvent event) {
switch (event.getType()) {
case None:
handleKeeperStateEvent(event);
break;
case NodeChildrenChanged:
handleChildWatchEvent(event);
break;
default:
break;
}
}
private void handleKeeperStateEvent(WatchedEvent event) {
Set<Watcher> savedAllWatches = new HashSet<Watcher>(allWatchesGauge.get());
for (Set<Watcher> watcherSet : childWatches.values()) {
synchronized (watcherSet) {
savedAllWatches.addAll(watcherSet);
}
}
for (Watcher watcher : savedAllWatches) {
watcher.process(event);
}
}
private void handleChildWatchEvent(WatchedEvent event) {
String path = event.getPath();
if (null == path) {
logger.warn("Received zookeeper watch event with null path : {}", event);
return;
}
Set<Watcher> watchers = childWatches.get(path);
if (null == watchers) {
return;
}
Set<Watcher> watchersToFire;
synchronized (watchers) {
watchersToFire = new HashSet<Watcher>(watchers.size());
watchersToFire.addAll(watchers);
}
for (Watcher watcher : watchersToFire) {
watcher.process(event);
}
}
}