CompressedKlassPointers.java

/*
 * Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package sun.jvm.hotspot.oops;

import sun.jvm.hotspot.utilities.Observable;
import sun.jvm.hotspot.utilities.Observer;

import sun.jvm.hotspot.debugger.Address;
import sun.jvm.hotspot.runtime.VM;
import sun.jvm.hotspot.types.AddressField;
import sun.jvm.hotspot.types.CIntegerField;
import sun.jvm.hotspot.types.Type;
import sun.jvm.hotspot.types.TypeDataBase;

public class CompressedKlassPointers {
  private static AddressField baseField;
  private static CIntegerField shiftField;

  static {
    VM.registerVMInitializedObserver(new Observer() {
        public void update(Observable o, Object data) {
          initialize(VM.getVM().getTypeDataBase());
        }
      });
  }

  private static boolean typeExists(TypeDataBase db, String type) {
      try {
          db.lookupType(type);
      } catch (RuntimeException e) {
          return false;
      }
      return true;
  }

  private static synchronized void initialize(TypeDataBase db) {
    Type type = db.lookupType("CompressedKlassPointers");

    baseField = type.getAddressField("_narrow_klass._base");
    shiftField = type.getCIntegerField("_narrow_klass._shift");
  }

  public CompressedKlassPointers() {
  }

  public static long getBase() {
    if (baseField.getValue() == null) {
      return 0;
    } else {
      return baseField.getValue().minus(null);
    }
  }

  public static int getShift() {
    return (int)shiftField.getValue();
  }
}