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/*
* Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
*
* Licensed 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. See accompanying
* LICENSE file.
*/
package com.gemstone.gemfire.cache;
/** A user-defined object defined in the {@link RegionAttributes} that is
* called synchronously before a region or entry in the cache is
* modified. The typical use for a CacheWriter is to update a database.
* Application writers should implement these methods to execute
* application-specific behavior before the cache is modified.
*
* Before the region is updated via a put, create, or destroy operation,
* GemFire will call a CacheWriter that is installed anywhere in any
* participating cache for that region, preferring a local CacheWriter
* if there is one. Usually there will be only one CacheWriter in
* the distributed system. If there are multiple CacheWriters
* available in the distributed system, the GemFire
* implementation always prefers one that is stored locally, or else picks one
* arbitrarily; in any case only one CacheWriter will be invoked.
*
*
The CacheWriter is capable of aborting the update to the cache by throwing
* a CacheWriterException. This exception or any runtime exception
* thrown by the CacheWriter will abort the operation and the
* exception will be propagated to the initiator of the operation, regardless
* of whether the initiator is in the same VM as the CacheWriter.
*
* @author Eric Zoerner
*
* @see AttributesFactory#setCacheWriter
* @see RegionAttributes#getCacheWriter
* @see AttributesMutator#setCacheWriter
* @since 3.0
*/
public interface CacheWriter extends CacheCallback {
/**
* Called before an entry is updated. The entry update is initiated by a put
* or a get that causes the loader to update an existing entry.
* The entry previously existed in the cache where the operation was
* initiated, although the old value may have been null. The entry being
* updated may or may not exist in the local cache where the CacheWriter is
* installed.
*
* @param event an EntryEvent that provides information about the operation in progress
* @throws CacheWriterException if thrown will abort the operation in progress,
* and the exception will be propagated back to caller that initiated
* the operation
* @see Region#put(Object, Object)
* @see Region#get(Object)
*/
public void beforeUpdate(EntryEvent event)
throws CacheWriterException;
/** Called before an entry is created. Entry creation is initiated by a
* create, a put, or a get.
* The CacheWriter can determine whether this value comes from a
* get or not by evaluating the {@link CacheEvent#getOperation() Operation}'s {@link Operation#isLoad()} method.
* The entry being created may already exist in the local cache where this CacheWriter
* is installed, but it does not yet exist in the cache where the operation was initiated.
* @param event an EntryEvent that provides information about the operation in progress
* @throws CacheWriterException if thrown will abort the operation in progress,
* and the exception will be propagated back to caller that initiated
* the operation
* @see Region#create(Object, Object)
* @see Region#put(Object, Object)
* @see Region#get(Object)
*/
public void beforeCreate(EntryEvent event)
throws CacheWriterException;
/**
* Called before an entry is destroyed. The entry being destroyed may or may
* not exist in the local cache where the CacheWriter is installed. This method
* is not called as a result of expiration or
* {@link Region#localDestroy(Object)}.
*
* @param event an EntryEvent that provides information about the operation in progress
* @throws CacheWriterException if thrown will abort the operation in progress,
* and the exception will be propagated back to caller that initiated
* the operation
*
* @see Region#destroy(Object)
*/
public void beforeDestroy(EntryEvent event)
throws CacheWriterException;
/**
* Called before a region is destroyed. The CacheWriter
* will not additionally be called for each entry that is destroyed
* in the region as a result of a region destroy. If the region's
* subregions have CacheWriters installed, then they
* will be called for the cascading subregion destroys.
* This method is not called as a result of
* expiration or {@link Region#localDestroyRegion()}. However, the
* {@link Region#close} method is invoked regardless of whether a
* region is destroyed locally. A non-local region destroy results
* in an invocation of {@link #beforeRegionDestroy} followed by an
* invocation of {@link Region#close}.
*
* WARNING: This method should not destroy or create any regions itself or a
* deadlock will occur.
*
* @param event
* a RegionEvent that provides information about the operation
*
* @throws CacheWriterException
* if thrown, will abort the operation in progress, and the
* exception will be propagated back to the caller that
* initiated the operation
*
* @see Region#destroyRegion()
*/
public void beforeRegionDestroy(RegionEvent event)
throws CacheWriterException;
/**
* Called before a region is cleared. The CacheWriter
* will not additionally be called for each entry that is cleared
* in the region as a result of a region clear.
*
*
* WARNING: This method should not clear/destroy any regions
*
*
* @param event
* a RegionEvent that provides information about the operation
*
* @throws CacheWriterException
* if thrown, will abort the operation in progress, and the
* exception will be propagated back to the caller that
* initiated the operation
*
* @see Region#clear
*/
public void beforeRegionClear(RegionEvent event)
throws CacheWriterException;
}