/*
* 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.
*/
/*
* Created on Sep 12, 2005
*
*
*/
package org.apache.geode.internal.cache;
/**
* This class is intended to hold a single 'observer' which will receive callbacks from the
* Distributed/Local Region when events like clear take place. There can be only one such observer
* at a time. If no observer is needed, this member variable should point to an object with
* 'do-nothing' methods, such as CacheObserverAdapter.
*
* Code which wishes to observe events during Region clear should do so using the following
* technique:
*
* class MyCacheObserver extends CacheObserverAdapter { // ... override methods of interest ... }
*
* CacheObserver old = CacheObserverHolder.setInstance(new MyCacheObserver());
* org.apache.geode.internal.cache.LocalRegion.ISSUE_CALLBACKS_TO_CACHE_OBSERVER=true;
*
* try { Call region methods here } finally { // reset to the original CacheObserver.
* CacheObserverHolder.setInstance(old); }
*
* The Region code will call methods on this static member using the following technique:
*
* CacheObserver observer = CacheObserverHolder.getInstance(); try {
* observer.startMethod(arguments); doSomething(); } finally { observer.stopMethod(arguments); }
*
*/
public class CacheObserverHolder {
/**
* The default 'do-nothing' query observer *
*/
private static final CacheObserver NO_OBSERVER = new CacheObserverAdapter();
/**
* The current observer which will be notified of all query events.
*/
private static CacheObserver _instance = NO_OBSERVER;
/**
* Set the given observer to be notified of query events. Returns the current observer.
*/
public static final CacheObserver setInstance(CacheObserver observer) {
if (observer == null)
observer = NO_OBSERVER;
CacheObserver oldObserver = _instance;
_instance = observer;
return oldObserver;
}
/** Return the current QueryObserver instance */
public static final CacheObserver getInstance() {
return _instance;
}
}