LazyReplicatedMap.java
/*
* 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.
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package org.apache.catalina.tribes.tipis;
import java.io.Serializable;
import org.apache.catalina.tribes.Channel;
import org.apache.catalina.tribes.ChannelException;
import org.apache.catalina.tribes.Member;
import org.apache.catalina.tribes.UniqueId;
import org.apache.catalina.tribes.util.Arrays;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
/**
* A smart implementation of a stateful replicated map. uses primary/secondary backup strategy.
* One node is always the primary and one node is always the backup.
* This map is synchronized across a cluster, and only has one backup member.<br>
* A perfect usage for this map would be a session map for a session manager in a clustered environment.<br>
* The only way to modify this list is to use the <code>put, putAll, remove</code> methods.
* entrySet, entrySetFull, keySet, keySetFull, returns all non modifiable sets.<br><br>
* If objects (values) in the map change without invoking <code>put()</code> or <code>remove()</code>
* the data can be distributed using two different methods:<br>
* <code>replicate(boolean)</code> and <code>replicate(Object, boolean)</code><br>
* These two methods are very important two understand. The map can work with two set of value objects:<br>
* 1. Serializable - the entire object gets serialized each time it is replicated<br>
* 2. ReplicatedMapEntry - this interface allows for a isDirty() flag and to replicate diffs if desired.<br>
* Implementing the <code>ReplicatedMapEntry</code> interface allows you to decide what objects
* get replicated and how much data gets replicated each time.<br>
* If you implement a smart AOP mechanism to detect changes in underlying objects, you can replicate
* only those changes by implementing the ReplicatedMapEntry interface, and return true when isDiffable()
* is invoked.<br><br>
*
* This map implementation doesn't have a background thread running to replicate changes.
* If you do have changes without invoking put/remove then you need to invoke one of the following methods:
* <ul>
* <li><code>replicate(Object,boolean)</code> - replicates only the object that belongs to the key</li>
* <li><code>replicate(boolean)</code> - Scans the entire map for changes and replicates data</li>
* </ul>
* the <code>boolean</code> value in the <code>replicate</code> method used to decide
* whether to only replicate objects that implement the <code>ReplicatedMapEntry</code> interface
* or to replicate all objects. If an object doesn't implement the <code>ReplicatedMapEntry</code> interface
* each time the object gets replicated the entire object gets serialized, hence a call to <code>replicate(true)</code>
* will replicate all objects in this map that are using this node as primary.
*
* <br><br><b>REMEMBER TO CALL</b> <code>breakdown()</code> when you are done with the map to
* avoid memory leaks.<br><br>
* TODO implement periodic sync/transfer thread
*
* @param <K> The type of Key
* @param <V> The type of Value
*/
public class LazyReplicatedMap<K,V> extends AbstractReplicatedMap<K,V> {
private static final long serialVersionUID = 1L;
// Lazy init to support serialization
private transient volatile Log log;
//------------------------------------------------------------------------------
// CONSTRUCTORS / DESTRUCTORS
//------------------------------------------------------------------------------
/**
* Creates a new map
* @param owner The map owner
* @param channel The channel to use for communication
* @param timeout long - timeout for RPC messages
* @param mapContextName String - unique name for this map, to allow multiple maps per channel
* @param initialCapacity int - the size of this map, see HashMap
* @param loadFactor float - load factor, see HashMap
* @param cls Class loaders
*/
public LazyReplicatedMap(MapOwner owner, Channel channel, long timeout, String mapContextName, int initialCapacity, float loadFactor, ClassLoader[] cls) {
super(owner,channel,timeout,mapContextName,initialCapacity,loadFactor, Channel.SEND_OPTIONS_DEFAULT,cls, true);
}
/**
* Creates a new map
* @param owner The map owner
* @param channel The channel to use for communication
* @param timeout long - timeout for RPC messages
* @param mapContextName String - unique name for this map, to allow multiple maps per channel
* @param initialCapacity int - the size of this map, see HashMap
* @param cls Class loaders
*/
public LazyReplicatedMap(MapOwner owner, Channel channel, long timeout, String mapContextName, int initialCapacity, ClassLoader[] cls) {
super(owner, channel, timeout, mapContextName, initialCapacity, DEFAULT_LOAD_FACTOR,
Channel.SEND_OPTIONS_DEFAULT, cls, true);
}
/**
* Creates a new map
* @param owner The map owner
* @param channel The channel to use for communication
* @param timeout long - timeout for RPC messages
* @param mapContextName String - unique name for this map, to allow multiple maps per channel
* @param cls Class loaders
*/
public LazyReplicatedMap(MapOwner owner, Channel channel, long timeout, String mapContextName, ClassLoader[] cls) {
super(owner, channel, timeout, mapContextName, DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR,
Channel.SEND_OPTIONS_DEFAULT, cls, true);
}
/**
* Creates a new map
* @param owner The map owner
* @param channel The channel to use for communication
* @param timeout long - timeout for RPC messages
* @param mapContextName String - unique name for this map, to allow multiple maps per channel
* @param cls Class loaders
* @param terminate boolean - Flag for whether to terminate this map that failed to start.
*/
public LazyReplicatedMap(MapOwner owner, Channel channel, long timeout, String mapContextName, ClassLoader[] cls, boolean terminate) {
super(owner, channel, timeout, mapContextName, DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR,
Channel.SEND_OPTIONS_DEFAULT, cls, terminate);
}
//------------------------------------------------------------------------------
// METHODS TO OVERRIDE
//------------------------------------------------------------------------------
@Override
protected int getStateMessageType() {
return AbstractReplicatedMap.MapMessage.MSG_STATE;
}
@Override
protected int getReplicateMessageType() {
return AbstractReplicatedMap.MapMessage.MSG_BACKUP;
}
@Override
protected Member[] publishEntryInfo(Object key, Object value) throws ChannelException {
Log log = getLog();
if (! (key instanceof Serializable && value instanceof Serializable) ) {
return new Member[0];
}
Member[] members = getMapMembers();
int firstIdx = getNextBackupIndex();
int nextIdx = firstIdx;
Member[] backup = new Member[0];
//there are no backups
if ( members.length == 0 || firstIdx == -1 ) {
return backup;
}
boolean success = false;
do {
//select a backup node
Member next = members[nextIdx];
//increment for the next round of back up selection
nextIdx = nextIdx + 1;
if ( nextIdx >= members.length ) {
nextIdx = 0;
}
if (next == null) {
continue;
}
MapMessage msg = null;
try {
Member[] tmpBackup = wrap(next);
//publish the backup data to one node
msg = new MapMessage(getMapContextName(), MapMessage.MSG_BACKUP, false,
(Serializable) key, (Serializable) value, null, channel.getLocalMember(false), tmpBackup);
if ( log.isTraceEnabled() ) {
log.trace("Publishing backup data:"+msg+" to: "+next.getName());
}
UniqueId id = getChannel().send(tmpBackup, msg, getChannelSendOptions());
if ( log.isTraceEnabled() ) {
log.trace("Data published:"+msg+" msg Id:"+id);
}
//we published out to a backup, mark the test success
success = true;
backup = tmpBackup;
}catch ( ChannelException x ) {
log.error(sm.getString("lazyReplicatedMap.unableReplicate.backup", key, next, x.getMessage()), x);
continue;
}
try {
//publish the data out to all nodes
Member[] proxies = excludeFromSet(backup, getMapMembers());
if (success && proxies.length > 0 ) {
msg = new MapMessage(getMapContextName(), MapMessage.MSG_PROXY, false,
(Serializable) key, null, null, channel.getLocalMember(false),backup);
if ( log.isTraceEnabled() ) {
log.trace("Publishing proxy data:"+msg+" to: "+Arrays.toNameString(proxies));
}
getChannel().send(proxies, msg, getChannelSendOptions());
}
}catch ( ChannelException x ) {
//log the error, but proceed, this should only happen if a node went down,
//and if the node went down, then it can't receive the message, the others
//should still get it.
log.error(sm.getString("lazyReplicatedMap.unableReplicate.proxy", key, next, x.getMessage()), x);
}
} while ( !success && (firstIdx!=nextIdx));
return backup;
}
private Log getLog() {
if (log == null) {
synchronized (this) {
if (log == null) {
log = LogFactory.getLog(LazyReplicatedMap.class);
}
}
}
return log;
}
}