/**
* 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;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Date;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.zookeeper.common.Time;
/**
* ExpiryQueue tracks elements in time sorted fixed duration buckets.
* It's used by SessionTrackerImpl to expire sessions and NIOServerCnxnFactory
* to expire connections.
*/
public class ExpiryQueue<E> {
private final ConcurrentHashMap<E, Long> elemMap =
new ConcurrentHashMap<E, Long>();
/**
* The maximum number of buckets is equal to max timeout/expirationInterval,
* so the expirationInterval should not be too small compared to the
* max timeout that this expiry queue needs to maintain.
*/
private final ConcurrentHashMap<Long, Set<E>> expiryMap =
new ConcurrentHashMap<Long, Set<E>>();
private final AtomicLong nextExpirationTime = new AtomicLong();
private final int expirationInterval;
public ExpiryQueue(int expirationInterval) {
this.expirationInterval = expirationInterval;
nextExpirationTime.set(roundToNextInterval(Time.currentElapsedTime()));
}
private long roundToNextInterval(long time) {
return (time / expirationInterval + 1) * expirationInterval;
}
/**
* Removes element from the queue.
* @param elem element to remove
* @return time at which the element was set to expire, or null if
* it wasn't present
*/
public Long remove(E elem) {
Long expiryTime = elemMap.remove(elem);
if (expiryTime != null) {
Set<E> set = expiryMap.get(expiryTime);
if (set != null) {
set.remove(elem);
// We don't need to worry about removing empty sets,
// they'll eventually be removed when they expire.
}
}
return expiryTime;
}
/**
* Adds or updates expiration time for element in queue, rounding the
* timeout to the expiry interval bucketed used by this queue.
* @param elem element to add/update
* @param timeout timout in milliseconds
* @return time at which the element is now set to expire if
* changed, or null if unchanged
*/
public Long update(E elem, int timeout) {
Long prevExpiryTime = elemMap.get(elem);
long now = Time.currentElapsedTime();
Long newExpiryTime = roundToNextInterval(now + timeout);
if (newExpiryTime.equals(prevExpiryTime)) {
// No change, so nothing to update
return null;
}
// First add the elem to the new expiry time bucket in expiryMap.
Set<E> set = expiryMap.get(newExpiryTime);
if (set == null) {
// Construct a ConcurrentHashSet using a ConcurrentHashMap
set = Collections.newSetFromMap(
new ConcurrentHashMap<E, Boolean>());
// Put the new set in the map, but only if another thread
// hasn't beaten us to it
Set<E> existingSet = expiryMap.putIfAbsent(newExpiryTime, set);
if (existingSet != null) {
set = existingSet;
}
}
set.add(elem);
// Map the elem to the new expiry time. If a different previous
// mapping was present, clean up the previous expiry bucket.
prevExpiryTime = elemMap.put(elem, newExpiryTime);
if (prevExpiryTime != null && !newExpiryTime.equals(prevExpiryTime)) {
Set<E> prevSet = expiryMap.get(prevExpiryTime);
if (prevSet != null) {
prevSet.remove(elem);
}
}
return newExpiryTime;
}
/**
* @return milliseconds until next expiration time, or 0 if has already past
*/
public long getWaitTime() {
long now = Time.currentElapsedTime();
long expirationTime = nextExpirationTime.get();
return now < expirationTime ? (expirationTime - now) : 0L;
}
/**
* Remove the next expired set of elements from expireMap. This method needs
* to be called frequently enough by checking getWaitTime(), otherwise there
* will be a backlog of empty sets queued up in expiryMap.
*
* @return next set of expired elements, or an empty set if none are
* ready
*/
public Set<E> poll() {
long now = Time.currentElapsedTime();
long expirationTime = nextExpirationTime.get();
if (now < expirationTime) {
return Collections.emptySet();
}
Set<E> set = null;
long newExpirationTime = expirationTime + expirationInterval;
if (nextExpirationTime.compareAndSet(
expirationTime, newExpirationTime)) {
set = expiryMap.remove(expirationTime);
}
if (set == null) {
return Collections.emptySet();
}
return set;
}
public void dump(PrintWriter pwriter) {
pwriter.print("Sets (");
pwriter.print(expiryMap.size());
pwriter.print(")/(");
pwriter.print(elemMap.size());
pwriter.println("):");
ArrayList<Long> keys = new ArrayList<Long>(expiryMap.keySet());
Collections.sort(keys);
for (long time : keys) {
Set<E> set = expiryMap.get(time);
if (set != null) {
pwriter.print(set.size());
pwriter.print(" expire at ");
pwriter.print(Time.elapsedTimeToDate(time));
pwriter.println(":");
for (E elem : set) {
pwriter.print("\t");
pwriter.println(elem.toString());
}
}
}
}
/**
* Returns an unmodifiable view of the expiration time -> elements mapping.
*/
public Map<Long, Set<E>> getExpiryMap() {
return Collections.unmodifiableMap(expiryMap);
}
}