001    /*
002     *  This file is part of the Jikes RVM project (http://jikesrvm.org).
003     *
004     *  This file is licensed to You under the Eclipse Public License (EPL);
005     *  You may not use this file except in compliance with the License. You
006     *  may obtain a copy of the License at
007     *
008     *      http://www.opensource.org/licenses/eclipse-1.0.php
009     *
010     *  See the COPYRIGHT.txt file distributed with this work for information
011     *  regarding copyright ownership.
012     */
013    package org.mmtk.plan.refcount.backuptrace;
014    
015    import org.mmtk.plan.TraceLocal;
016    import org.mmtk.plan.Trace;
017    import org.mmtk.plan.refcount.RCBase;
018    import org.mmtk.plan.refcount.RCHeader;
019    
020    import org.vmmagic.pragma.*;
021    import org.vmmagic.unboxed.*;
022    
023    /**
024     * This class implements the thread-local core functionality for a transitive
025     * closure over the heap graph.
026     */
027    @Uninterruptible
028    public final class BTTraceLocal extends TraceLocal {
029      /**
030       * Constructor
031       */
032      public BTTraceLocal(Trace trace) {
033        super(trace);
034      }
035    
036      /****************************************************************************
037       *
038       * Externally visible Object processing and tracing
039       */
040    
041      /**
042       * Is the specified object reachable?
043       *
044       * @param object The object.
045       * @return <code>true</code> if the object is reachable.
046       */
047      @Override
048      public boolean isLive(ObjectReference object) {
049        return !RCBase.isRCObject(object) || RCHeader.isMarked(object);
050      }
051    
052      /**
053       * When we trace a non-root object we do nothing.
054       *
055       * @param object The object to be traced.
056       * @return The new reference to the same object instance.
057       */
058      @Override
059      @Inline
060      public ObjectReference traceObject(ObjectReference object) {
061        if (RCBase.isRCObject(object)) {
062          if (RCHeader.testAndMark(object)) {
063            RCHeader.initRC(object);
064            processNode(object);
065          } else {
066            RCHeader.incRC(object);
067          }
068        }
069        return object;
070      }
071    }