/*
 *  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.marksweep;

import org.mmtk.plan.*;
import org.mmtk.policy.MarkSweepSpace;
import org.mmtk.policy.Space;
import org.mmtk.utility.heap.VMRequest;

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

/**
 * This class implements the global state of a simple mark-sweep collector.
 *
 * All plans make a clear distinction between <i>global</i> and
 * <i>thread-local</i> activities, and divides global and local state
 * into separate class hierarchies.  Global activities must be
 * synchronized, whereas no synchronization is required for
 * thread-local activities.  There is a single instance of Plan (or the
 * appropriate sub-class), and a 1:1 mapping of PlanLocal to "kernel
 * threads" (aka CPUs).  Thus instance
 * methods of PlanLocal allow fast, unsychronized access to functions such as
 * allocation and collection.
 *
 * The global instance defines and manages static resources
 * (such as memory and virtual memory resources).  This mapping of threads to
 * instances is crucial to understanding the correctness and
 * performance properties of MMTk plans.
 */
@Uninterruptible
public class MS extends StopTheWorld {

  /****************************************************************************
   * Class variables
   */
  public static final MarkSweepSpace msSpace = new MarkSweepSpace("ms", DEFAULT_POLL_FREQUENCY, VMRequest.create());
  public static final int MARK_SWEEP = msSpace.getDescriptor();

  public static final int SCAN_MARK = 0;


  /****************************************************************************
   * Instance variables
   */
  public final Trace msTrace = new Trace(metaDataSpace);


  /*****************************************************************************
   * Collection
   */

  /**
   * Perform a (global) collection phase.
   *
   * @param phaseId Collection phase to execute.
   */
  @Inline
  @Override
  public void collectionPhase(short phaseId) {

    if (phaseId == PREPARE) {
      super.collectionPhase(phaseId);
      msTrace.prepare();
      msSpace.prepare(true);
      return;
    }

    if (phaseId == CLOSURE) {
      msTrace.prepare();
      return;
    }
    if (phaseId == RELEASE) {
      msTrace.release();
      msSpace.release();
      super.collectionPhase(phaseId);
      return;
    }

    super.collectionPhase(phaseId);
  }

  /*****************************************************************************
   * Accounting
   */

  /**
   * Return the number of pages reserved for use given the pending
   * allocation.  The superclass accounts for its spaces, we just
   * augment this with the mark-sweep space's contribution.
   *
   * @return The number of pages reserved given the pending
   * allocation, excluding space reserved for copying.
   */
  @Override
  public int getPagesUsed() {
    return (msSpace.reservedPages() + super.getPagesUsed());
  }

  /**
   * Calculate the number of pages a collection is required to free to satisfy
   * outstanding allocation requests.
   *
   * @return the number of pages a collection is required to free to satisfy
   * outstanding allocation requests.
   */
  @Override
  public int getPagesRequired() {
    return super.getPagesRequired() + msSpace.requiredPages();
  }


  /*****************************************************************************
   * Miscellaneous
   */

  /**
   * @see org.mmtk.plan.Plan#willNeverMove
   *
   * @param object Object in question
   * @return True if the object will never move
   */
  @Override
  public boolean willNeverMove(ObjectReference object) {
    if (Space.isInSpace(MARK_SWEEP, object))
      return true;
    return super.willNeverMove(object);
  }

  /**
   * Register specialized methods.
   */
  @Interruptible
  @Override
  protected void registerSpecializedMethods() {
    TransitiveClosure.registerSpecializedScan(SCAN_MARK, MSTraceLocal.class);
    super.registerSpecializedMethods();
  }
}