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.refcount.RCHeader;
016import org.mmtk.policy.ExplicitFreeListSpace;
017
018import org.vmmagic.pragma.*;
019import org.vmmagic.unboxed.*;
020
021/**
022 * This class implements the thread-local core functionality for a transitive
023 * closure over the heap graph.
024 */
025@Uninterruptible
026public final class BTSweeper extends ExplicitFreeListSpace.Sweeper {
027
028  @Override
029  public boolean sweepCell(ObjectReference object) {
030    if (!RCHeader.isMarked(object)) {
031      return true;
032    } else {
033      RCHeader.clearMarked(object);
034    }
035    return false;
036  }
037}