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 */
013package org.mmtk.plan.generational;
014
015import org.mmtk.plan.StopTheWorldConstraints;
016
017import org.mmtk.policy.CopySpace;
018import org.mmtk.policy.Space;
019
020import org.vmmagic.pragma.*;
021
022/**
023 * This class and its subclasses communicate to the host VM/Runtime
024 * any features of the selected plan that it needs to know.  This is
025 * separate from the main Plan/PlanLocal class in order to bypass any
026 * issues with ordering of static initialization.
027 */
028@Uninterruptible
029public class GenConstraints extends StopTheWorldConstraints {
030
031  @Override
032  public boolean generational() {
033    return true;
034  }
035
036  @Override
037  public boolean movesObjects() {
038    return true;
039  }
040
041  @Override
042  public int gcHeaderBits() {
043    return CopySpace.LOCAL_GC_BITS_REQUIRED;
044  }
045
046  @Override
047  public int gcHeaderWords() {
048    return CopySpace.GC_HEADER_WORDS_REQUIRED;
049  }
050
051  @Override
052  public boolean needsObjectReferenceWriteBarrier() {
053    return true;
054  }
055
056  @Override
057  public boolean needsObjectReferenceNonHeapWriteBarrier() {
058    return Gen.USE_NON_HEAP_OBJECT_REFERENCE_WRITE_BARRIER;
059  }
060
061  @Override
062  public boolean objectReferenceBulkCopySupported() {
063    return true;
064  }
065
066  @Override
067  public int numSpecializedScans() {
068    return 2;
069  }
070
071  @Override
072  public boolean needsLogBitInHeader() {
073    return Gen.USE_OBJECT_BARRIER;
074  }
075
076  /**
077   * @return The maximum size of an object that may be allocated directly into the nursery
078   */
079  @Override
080  public int maxNonLOSDefaultAllocBytes() {
081    /*
082     * If the nursery is discontiguous, the maximum object is essentially unbounded.  In
083     * a contiguous nursery, we can't attempt to nursery-allocate objects larger than the
084     * available nursery virtual memory.
085     */
086    return  Gen.USE_DISCONTIGUOUS_NURSERY ?
087        org.mmtk.utility.Constants.MAX_INT :
088        Space.getFracAvailable(Gen.NURSERY_VM_FRACTION).toInt();
089  }
090
091}