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.refcount.RCHeader;
016    import org.mmtk.policy.ExplicitFreeListSpace;
017    
018    import org.vmmagic.pragma.*;
019    import 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
026    public 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    }