/*
* Copyright (c) 2008, Rickard Öberg. 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 org.qi4j.spi.entitystore;
import org.qi4j.api.Qi4j;
import org.qi4j.api.concern.ConcernOf;
import org.qi4j.api.entity.EntityDescriptor;
import org.qi4j.api.entity.EntityReference;
import org.qi4j.api.injection.scope.Structure;
import org.qi4j.api.injection.scope.This;
import org.qi4j.api.structure.Module;
import org.qi4j.api.usecase.Usecase;
import org.qi4j.spi.entity.EntityState;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Concern that helps EntityStores do concurrent modification checks.
* <p>
* It caches the versions of state that it loads, and forgets them when
* the state is committed. For normal operation this means that it does
* not have to go down to the underlying store to get the current version.
* Whenever there is a concurrent modification the store will most likely
* have to check with the underlying store what the current version is.
* </p>
*/
public abstract class ConcurrentModificationCheckConcern
extends ConcernOf<EntityStore>
implements EntityStore
{
@This
private EntityStateVersions versions;
@Structure
private Qi4j api;
@Override
public EntityStoreUnitOfWork newUnitOfWork( Usecase usecase, Module module, long currentTime )
{
final EntityStoreUnitOfWork uow = next.newUnitOfWork( usecase, module, currentTime );
return new ConcurrentCheckingEntityStoreUnitOfWork( uow, api.dereference( versions ), module, currentTime );
}
private static class ConcurrentCheckingEntityStoreUnitOfWork
implements EntityStoreUnitOfWork
{
private final EntityStoreUnitOfWork uow;
private EntityStateVersions versions;
private Module module;
private long currentTime;
private List<EntityState> loaded = new ArrayList<EntityState>();
private ReentrantReadWriteLock lock = new ReentrantReadWriteLock( );
public ConcurrentCheckingEntityStoreUnitOfWork( EntityStoreUnitOfWork uow,
EntityStateVersions versions,
Module module,
long currentTime
)
{
this.uow = uow;
this.versions = versions;
this.module = module;
this.currentTime = currentTime;
}
@Override
public String identity()
{
return uow.identity();
}
@Override
public long currentTime()
{
return uow.currentTime();
}
@Override
public EntityState newEntityState( EntityReference anIdentity, EntityDescriptor entityDescriptor )
throws EntityStoreException
{
return uow.newEntityState( anIdentity, entityDescriptor );
}
@Override
public StateCommitter applyChanges()
throws EntityStoreException
{
lock.writeLock().lock();
try
{
versions.checkForConcurrentModification( loaded, module, currentTime );
final StateCommitter committer = uow.applyChanges();
return new StateCommitter()
{
@Override
public void commit()
{
committer.commit();
versions.forgetVersions( loaded );
lock.writeLock().unlock();
}
@Override
public void cancel()
{
committer.cancel();
versions.forgetVersions( loaded );
lock.writeLock().unlock();
}
};
} catch( EntityStoreException e )
{
lock.writeLock().unlock();
throw e;
}
}
@Override
public void discard()
{
try
{
uow.discard();
}
finally
{
lock.writeLock().lock();
try
{
versions.forgetVersions( loaded );
} finally
{
lock.writeLock().unlock();
}
}
}
@Override
public EntityState entityStateOf( EntityReference anIdentity )
throws EntityStoreException, EntityNotFoundException
{
lock.readLock().lock();
try
{
EntityState entityState = uow.entityStateOf( anIdentity );
versions.rememberVersion( entityState.identity(), entityState.version() );
loaded.add( entityState );
return entityState;
} finally
{
lock.readLock().unlock();
}
}
}
}