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     */
013    package org.jikesrvm.objectmodel;
014    
015    import org.jikesrvm.Constants;
016    import org.jikesrvm.mm.mminterface.MemoryManagerConstants;
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     */
026    public interface MiscHeaderConstants extends Constants {
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 */ int GC_TRACING_HEADER_WORDS =
033          (MemoryManagerConstants.GENERATE_GC_TRACE ? 3 : 0);
034      int GC_TRACING_HEADER_BYTES = GC_TRACING_HEADER_WORDS << LOG_BYTES_IN_ADDRESS;
035    
036      /**
037       * How many bytes are used by all misc header fields?
038       */
039      int NUM_BYTES_HEADER = GC_TRACING_HEADER_BYTES; // + YYY_HEADER_BYTES;
040    }