/*
 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
 *
 *  This file is licensed to You under the Eclipse Public License (EPL);
 *  You may not use this file except in compliance with the License. You
 *  may obtain a copy of the License at
 *
 *      http://www.opensource.org/licenses/eclipse-1.0.php
 *
 *  See the COPYRIGHT.txt file distributed with this work for information
 *  regarding copyright ownership.
 */
package org.mmtk.plan.markcompact;

import org.mmtk.plan.TraceLocal;
import org.mmtk.plan.Trace;
import org.mmtk.policy.Space;

import org.vmmagic.pragma.*;
import org.vmmagic.unboxed.*;

/**
 * This class implements the thread-local functionality for a transitive
 * closure over a mark-compact space during the forwarding phase.
 */
@Uninterruptible
public final class MCForwardTraceLocal extends TraceLocal {

  /**
   * @param trace the associated global trace
   */
  public MCForwardTraceLocal(Trace trace) {
    super(MC.SCAN_FORWARD, trace);
  }

  /****************************************************************************
   *
   * Externally visible Object processing and tracing
   */

  /**
   * {@inheritDoc}
   */
  @Override
  public boolean isLive(ObjectReference object) {
    if (object.isNull()) return false;
    if (Space.isInSpace(MC.MARK_COMPACT, object)) {
      return MC.mcSpace.isLive(object);
    }
    return super.isLive(object);
  }

  /**
   * {@inheritDoc}<p>
   *
   * In this instance, we refer objects in the mark-sweep space to the
   * msSpace for tracing, and defer to the superclass for all others.
   *
   * @param object The object to be traced.
   * @return The new reference to the same object instance.
   */
  @Override
  @Inline
  public ObjectReference traceObject(ObjectReference object) {
    if (object.isNull()) return object;
    if (Space.isInSpace(MC.MARK_COMPACT, object))
      return MC.mcSpace.traceForwardObject(this, object);
    return super.traceObject(object);
  }

  /**
   * Will this object move from this point on, during the current trace ?
   *
   * @param object The object to query.
   * @return {@code true} if the object will not move.
   */
  @Override
  public boolean willNotMoveInCurrentCollection(ObjectReference object) {
    return !Space.isInSpace(MC.MARK_COMPACT, object);
  }
}