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 */
013package org.mmtk.plan.refcount.backuptrace;
014
015import org.mmtk.plan.TraceLocal;
016import org.mmtk.plan.Trace;
017import org.mmtk.plan.refcount.RCBase;
018import org.mmtk.plan.refcount.RCHeader;
019
020import org.vmmagic.pragma.*;
021import 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
028public final class BTTraceLocal extends TraceLocal {
029
030  /**
031   * @param trace the associated global trace
032   */
033public BTTraceLocal(Trace trace) {
034    super(trace);
035  }
036
037  /****************************************************************************
038   *
039   * Externally visible Object processing and tracing
040   */
041
042  /**
043   * Is the specified object reachable?
044   *
045   * @param object The object.
046   * @return <code>true</code> if the object is reachable.
047   */
048  @Override
049  public boolean isLive(ObjectReference object) {
050    return !RCBase.isRCObject(object) || RCHeader.isMarked(object);
051  }
052
053  /**
054   * When we trace a non-root object we do nothing.
055   *
056   * @param object The object to be traced.
057   * @return The new reference to the same object instance.
058   */
059  @Override
060  @Inline
061  public ObjectReference traceObject(ObjectReference object) {
062    if (RCBase.isRCObject(object)) {
063      if (RCHeader.testAndMark(object)) {
064        RCHeader.initRC(object);
065        processNode(object);
066      } else {
067        RCHeader.incRC(object);
068      }
069    }
070    return object;
071  }
072}