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.semispace.gcspy;
014    
015    import org.mmtk.plan.Trace;
016    import org.mmtk.plan.semispace.SSTraceLocal;
017    import org.mmtk.policy.Space;
018    
019    import org.vmmagic.pragma.*;
020    import org.vmmagic.unboxed.*;
021    
022    /**
023     * This class implments the core functionality for a transitive
024     * closure over the heap graph.
025     */
026    @Uninterruptible
027    public final class SSGCspyTraceLocal extends SSTraceLocal {
028      /**
029       * Constructor
030       */
031      public SSGCspyTraceLocal(Trace trace) {
032        super(trace);
033      }
034    
035      /****************************************************************************
036       *
037       * Externally visible Object processing and tracing
038       */
039    
040      /**
041       * This method is the core method during the trace of the object graph.
042       * The role of this method is to:
043       *
044       * 1. Ensure the traced object is not collected.
045       * 2. If this is the first visit to the object enqueue it to be scanned.
046       * 3. Return the forwarded reference to the object.
047       *
048       * @param object The object to be traced.
049       * @return The new reference to the same object instance.
050       */
051      @Inline
052      public ObjectReference traceObject(ObjectReference object) {
053        if (object.isNull()) return object;
054        if (Space.isInSpace(SSGCspy.GCSPY, object))
055          return SSGCspy.gcspySpace.traceObject(this, object);
056        return super.traceObject(object);
057      }
058    
059      /**
060       * Will this object move from this point on, during the current trace ?
061       *
062       * @param object The object to query.
063       * @return True if the object will not move.
064       */
065      public boolean willNotMoveInCurrentCollection(ObjectReference object) {
066        if (Space.isInSpace(SSGCspy.GCSPY, object))
067          return true;
068        return super.willNotMoveInCurrentCollection(object);
069      }
070    }