/*
 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
 *
 *  This file is licensed to You under the Common Public License (CPL);
 *  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/cpl1.0.php
 *
 *  See the COPYRIGHT.txt file distributed with this work for information
 *  regarding copyright ownership.
 */
package org.mmtk.plan.generational;

import org.mmtk.plan.Plan;
import org.mmtk.plan.TraceLocal;
import org.mmtk.plan.Trace;
import org.mmtk.policy.Space;
import org.mmtk.utility.deque.*;
import org.mmtk.vm.VM;

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

/**
 * This abstract class implments the core functionality for a transitive
 * closure over the heap graph.
 */
@Uninterruptible public final class GenNurseryTraceLocal extends TraceLocal {

  /****************************************************************************
   *
   * Instance fields.
   */
  private final AddressDeque remset;
  private final AddressPairDeque arrayRemset;


  /**
   * Constructor
   */
  public GenNurseryTraceLocal(Trace trace, GenCollector plan) {
    super(Gen.SCAN_NURSERY, trace);
    this.remset = plan.remset;
    this.arrayRemset = plan.arrayRemset;
  }

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

  /**
   * Is the specified object live?
   *
   * @param object The object.
   * @return True if the object is live.
   */
  public boolean isLive(ObjectReference object) {
    if (object.isNull()) return false;
    if (object.toAddress().GE(Gen.NURSERY_START)) {
      if (object.toAddress().LT(Gen.NURSERY_END))
        return Gen.nurserySpace.isLive(object);
      else
        return Gen.ploSpace.isLive(object);
    }
    if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(super.isLive(object));
    return true;
  }

  /**
   * This method is the core method during the trace of the object graph.
   * The role of this method is to:
   *
   * 1. Ensure the traced object is not collected.
   * 2. If this is the first visit to the object enqueue it to be scanned.
   * 3. Return the forwarded reference to the object.
   *
   * @param object The object to be traced.
   * @return The new reference to the same object instance.
   */
  @Inline
  public ObjectReference traceObject(ObjectReference object) {
    if (object.toAddress().GE(Gen.NURSERY_START)) {
      if (object.toAddress().LT(Gen.NURSERY_END))
        return Gen.nurserySpace.traceObject(this, object, Gen.ALLOC_MATURE_MINORGC);
      else
        return Gen.ploSpace.traceObject(this, object);
    }
    return object;
  }

  /**
   * Process any remembered set entries.
   */
  @Inline
  protected void processRememberedSets() {
    logMessage(5, "processing remset");
    while (!remset.isEmpty()) {
      Address loc = remset.pop();
      processRootEdge(loc);
    }
    logMessage(5, "processing array remset");
    arrayRemset.flushLocal();
    while (!arrayRemset.isEmpty()) {
      Address start = arrayRemset.pop1();
      Address guard = arrayRemset.pop2();
      while (start.LT(guard)) {
        processRootEdge(start);
        start = start.plus(BYTES_IN_ADDRESS);
      }
    }
  }

  /**
   * Will the object move from now on during the collection.
   *
   * @param object The object to query.
   * @return True if the object is guaranteed not to move.
   */
  public boolean willNotMoveInCurrentCollection(ObjectReference object) {
    if (object.isNull()) return false;
    return object.toAddress().LT(Gen.NURSERY_START) || Space.isInSpace(Plan.PLOS, object);
  }

}