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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.pool.sizeof;

import java.lang.ref.SoftReference;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.IdentityHashMap;
import java.util.Stack;

import net.sf.ehcache.pool.sizeof.filter.SizeOfFilter;
import net.sf.ehcache.util.WeakIdentityConcurrentMap;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This will walk an object graph and let you execute some "function" along the way
 *
 * @author Alex Snaps
 */
final class ObjectGraphWalker {

    private static final Logger LOG = LoggerFactory.getLogger(ObjectGraphWalker.class);
    private static final String TC_INTERNAL_FIELD_PREFIX = "$__tc_";
    private static final String VERBOSE_DEBUG_LOGGING = "net.sf.ehcache.sizeof.verboseDebugLogging";

    private static final String CONTINUE_MESSAGE =
        "The configured limit of {0} object references was reached while attempting to calculate the size of the object graph." +
        " Severe performance degradation could occur if the sizing operation continues. This can be avoided by setting the CacheManger" +
        " or Cache  element's maxDepthExceededBehavior to \"abort\" or adding stop points with @IgnoreSizeOf annotations." +
        " If performance degradation is NOT an issue at the configured limit, raise the limit value using the CacheManager or Cache" +
        "  element's maxDepth attribute. For more information, see the Ehcache configuration documentation.";


    private static final String ABORT_MESSAGE =
        "The configured limit of {0} object references was reached while attempting to calculate the size of the object graph." +
        " This can be avoided by adding stop points with @IgnoreSizeOf annotations. Since the CacheManger or Cache " +
        " element's maxDepthExceededBehavior is set to \"abort\", the sizing operation has stopped and the reported cache size is not" +
        " accurate. If performance degradation is NOT an issue at the configured limit, raise the limit value using the CacheManager" +
        " or Cache  element's maxDepth attribute. For more information, see the Ehcache configuration documentation.";

    private static final boolean USE_VERBOSE_DEBUG_LOGGING;

    // Todo this is probably not what we want...
    private final WeakIdentityConcurrentMap, SoftReference>> fieldCache =
            new WeakIdentityConcurrentMap, SoftReference>>();
    private final WeakIdentityConcurrentMap, Boolean> classCache =
            new WeakIdentityConcurrentMap, Boolean>();

    private final SizeOfFilter sizeOfFilter;

    private final Visitor visitor;

    static {
        USE_VERBOSE_DEBUG_LOGGING = getVerboseSizeOfDebugLogging();
    }

    /**
     * Constructor
     *
     * @param visitor the visitor to use
     * @param filter the filtering
     * @see Visitor
     * @see SizeOfFilter
     */
    ObjectGraphWalker(Visitor visitor, SizeOfFilter filter) {
        this.visitor = visitor;
        this.sizeOfFilter = filter;
    }

    private static boolean getVerboseSizeOfDebugLogging() {

        String verboseString = System.getProperty(VERBOSE_DEBUG_LOGGING, "false").toLowerCase();

        return verboseString.equals("true");
    }

    /**
     * The visitor to execute the function on each node of the graph
     * This is only to be used for the sizing of an object graph in memory!
     */
    static interface Visitor {
        /**
         * The visit method executed on each node
         *
         * @param object the reference at that node
         * @return a long for you to do things with...
         */
        public long visit(Object object);
    }

    /**
     * Walk the graph and call into the "visitor"
     *
     * @param maxDepth maximum depth to traverse the object graph
     * @param abortWhenMaxDepthExceeded true if the object traversal should be aborted when the max depth is exceeded
     * @param root the roots of the objects (a shared graph will only be visited once)
     * @return the sum of all Visitor#visit returned values
     */
    long walk(int maxDepth, boolean abortWhenMaxDepthExceeded, Object... root) {
        StringBuilder traversalDebugMessage = null;
        long result = 0;
        boolean warned = false;
        try {
            Stack