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    import org.mmtk.vm.VM;
018    
019    import org.vmmagic.pragma.*;
020    import org.vmmagic.unboxed.*;
021    
022    /**
023     * This class implements the thread-local core functionality for a transitive
024     * closure over the heap graph.
025     */
026    @Uninterruptible
027    public final class BTSweeper extends ExplicitFreeListSpace.Sweeper {
028    
029      private final BTDecMarked sdm = new BTDecMarked();
030    
031      public boolean sweepCell(ObjectReference object) {
032        if (!RCHeader.isMarked(object)) {
033          VM.scanning.scanObject(sdm, object);
034          return true;
035        } else {
036          RCHeader.clearMarked(object);
037        }
038        return false;
039      }
040    }