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/*
* Copyright 2006-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. 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.
*/
package com.amazon.carbonado.repo.indexed;
import com.amazon.carbonado.util.SoftValuedCache;
import com.amazon.carbonado.Storable;
import com.amazon.carbonado.SupportException;
import com.amazon.carbonado.info.StorableIndex;
import com.amazon.carbonado.info.StorableProperty;
import com.amazon.carbonado.synthetic.SyntheticStorableReferenceAccess;
import com.amazon.carbonado.synthetic.SyntheticStorableReferenceBuilder;
/**
* IndexEntryGenerator creates new kinds of Storables suitable for indexing a
* master Storable.
*
* @author Brian S O'Neill
* @author Don Schneider
*
*/
class IndexEntryGenerator <S extends Storable> {
private static final SoftValuedCache<StorableIndex, SyntheticStorableReferenceAccess> cCache =
SoftValuedCache.newCache(11);
/**
* Returns a new or cached index access instance. The caching of accessors
* is soft, so if no references remain to a given instance it may be
* garbage collected. A subsequent call will return a newly created
* instance.
*
* <p>In addition to generating an index entry storable, the accessor
* contains methods to operate on it. Care must be taken to ensure that the
* index entry instances are of the same type that the accessor expects.
* Since the accessor may be garbage collected freely of the generated
* index entry class, it is possible for index entries to be passed to a
* accessor instance that does not understand it. For example:
*
* <pre>
* StorableIndex index = ...
* Class indexEntryClass = IndexEntryGenerator.getIndexAccess(index).getReferenceClass();
* ...
* garbage collection
* ...
* Storable indexEntry = instance of indexEntryClass
* // Might fail because generator instance is new
* IndexEntryGenerator.getIndexAccess(index).copyFromMaster(indexEntry, master);
* </pre>
*
* The above code can be fixed by saving a local reference to the accessor:
*
* <pre>
* StorableIndex index = ...
* SyntheticStorableReferenceAccess access = IndexEntryGenerator.getIndexAccess(index);
* Class indexEntryClass = access.getReferenceClass();
* ...
* Storable indexEntry = instance of indexEntryClass
* access.copyFromMaster(indexEntry, master);
* </pre>
*
* @throws SupportException if any non-primary key property doesn't have a
* public read method.
*/
public static <S extends Storable>
SyntheticStorableReferenceAccess<S> getIndexAccess(StorableIndex<S> index)
throws SupportException
{
// Strip out index property not related to its identity.
index = index.clustered(false);
synchronized (cCache) {
SyntheticStorableReferenceAccess<S> access = cCache.get(index);
if (access != null) {
return access;
}
// Need to try to find the base type. This is an awkward way to do
// it, but we have nothing better available to us
Class<S> type = index.getProperty(0).getEnclosingType();
SyntheticStorableReferenceBuilder<S> builder =
new SyntheticStorableReferenceBuilder<S>(type, index.isUnique());
for (int i=0; i<index.getPropertyCount(); i++) {
StorableProperty<S> source = index.getProperty(i);
builder.addKeyProperty(source.getName(), index.getPropertyDirection(i));
}
builder.build();
access = builder.getReferenceAccess();
cCache.put(index, access);
return access;
}
}
private IndexEntryGenerator() {
}
}
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