    001    // Copyright 2009, 2011, 2012 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.ioc.internal.services;
    016
    017    import org.apache.tapestry5.ioc.ObjectCreator;
    018    import org.apache.tapestry5.ioc.internal.util.LockSupport;
    019
    020    /**
    021     * An {@link org.apache.tapestry5.ioc.ObjectCreator} that delegates to another
    022     * {@link org.apache.tapestry5.ioc.ObjectCreator} and caches the result.
    023     */
    024    public class CachingObjectCreator<T> extends LockSupport implements ObjectCreator<T>
    025    {
    026        private boolean cached;
    027
    028        private T cachedValue;
    029
    030        private ObjectCreator<T> delegate;
    031
    032        public CachingObjectCreator(ObjectCreator<T> delegate)
    033        {
    034            this.delegate = delegate;
    035        }
    036
    037        public T createObject()
    038        {
    039            try
    040            {
    041                acquireReadLock();
    042
    043                if (!cached)
    044                {
    045                    cacheValueFromDelegate();
    046                }
    047
    048                return cachedValue;
    049            } finally
    050            {
    051                releaseReadLock();
    052            }
    053        }
    054
    055        private void cacheValueFromDelegate()
    056        {
    057            try
    058            {
    059                upgradeReadLockToWriteLock();
    060
    061                if (!cached)
    062                {
    063                    cachedValue = delegate.createObject();
    064                    cached = true;
    065                    delegate = null;
    066                }
    067            } finally
    068            {
    069                downgradeWriteLockToReadLock();
    070            }
    071        }
    072    }