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Ehcache is an open source, standards-based cache used to boost performance, offload the database and simplify scalability. Ehcache is robust, proven and full-featured and this has made it the most widely-used Java-based cache.

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/**
 *  Copyright Terracotta, Inc.
 *
 *  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 net.sf.ehcache.store;

import net.sf.ehcache.CacheException;
import net.sf.ehcache.Ehcache;
import net.sf.ehcache.distribution.RemoteCacheException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Iterator;

/**
 * @author Alex Snaps
 */
public class DiskStoreBootstrapCacheLoader extends MemoryLimitedCacheLoader {

    private static final Logger LOG = LoggerFactory.getLogger(DiskStoreBootstrapCacheLoader.class);

    private final boolean asynchronous;

    /**
     * Constructor for loader
     * @param asynchronous whether load is asynchronous or synchronous
     */
    public DiskStoreBootstrapCacheLoader(final boolean asynchronous) {
        this.asynchronous = asynchronous;
    }

    /**
     * {@inheritDoc}
     */
    public void load(final Ehcache cache) throws CacheException {
        if (cache.getCacheConfiguration().isDiskPersistent()) {
            if (asynchronous) {
                BootstrapThread thread = new BootstrapThread(cache);
                thread.start();
            } else {
                doLoad(cache);
            }
        } else {
            LOG.warn("Cache '" + cache.getName() + "' isn't disk persistent, nothing to laod from!");
        }
    }

    /**
     * Performs bootstrap loading.  May be executed on a independent thread.
     */
    protected void doLoad(Ehcache cache) {
        int loadedElements = 0;
        final Iterator iterator = cache.getKeys().iterator();
        while (iterator.hasNext() && !isInMemoryLimitReached(cache, loadedElements)) {
            if (cache.get(iterator.next()) != null) {
                ++loadedElements;
            }
        }
        LOG.debug("Loaded {} elements from disk into heap for cache {}", loadedElements, cache.getName());
    }

    /**
     * {@inheritDoc}
     */
    public boolean isAsynchronous() {
        return asynchronous;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    /**
     * A background daemon thread that asynchronously calls doLoad
     */
    private final class BootstrapThread extends Thread {
        private final Ehcache cache;

        public BootstrapThread(Ehcache cache) {
            super("Bootstrap Thread for cache " + cache.getName());
            this.cache = cache;
            setDaemon(true);
            setPriority(Thread.NORM_PRIORITY);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void run() {
            try {
                doLoad(cache);
            } catch (RemoteCacheException e) {
                LOG.warn("Error asynchronously performing bootstrap. The cause was: " + e.getMessage(), e);
            }
        }
    }
}