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.jikesrvm.objectmodel;
014
015import static org.jikesrvm.mm.mminterface.MemoryManagerConstants.GENERATE_GC_TRACE;
016import static org.jikesrvm.runtime.UnboxedSizeConstants.LOG_BYTES_IN_ADDRESS;
017
018/**
019 * Defines other header words not used for
020 * core Java language support of memory allocation.
021 * Typically these are extra header words used for various
022 * kinds of instrumentation or profiling.
023 *
024 * @see ObjectModel
025 */
026public final class MiscHeaderConstants {
027
028  /*********************
029   * Support for GC Tracing; uses either 0 or 3 words of MISC HEADER
030   */
031
032  /* amount by which tracing causes headers to grow */
033  public static final int GC_TRACING_HEADER_WORDS =
034      (GENERATE_GC_TRACE ? 3 : 0);
035  public static final int GC_TRACING_HEADER_BYTES = GC_TRACING_HEADER_WORDS << LOG_BYTES_IN_ADDRESS;
036
037  /**
038   * How many bytes are used by all misc header fields?
039   */
040  public static final int NUM_BYTES_HEADER = GC_TRACING_HEADER_BYTES; // + YYY_HEADER_BYTES;
041
042  private MiscHeaderConstants() {
043    // prevent instantiation
044  }
045
046}