JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2000, 2019, 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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
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 */

package sun.jvm.hotspot.oops;

import java.util.Observable;
import java.util.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 CompressedOops {
  private static AddressField baseField;
  private static CIntegerField shiftField;

  public enum Mode {
    UnscaledNarrowOop,
    ZeroBasedNarrowOop,
    HeapBasedNarrowOop
  }

  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("CompressedOops");

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

  public CompressedOops() {
  }
  public static String modeToString(Mode mode) {
    switch (mode) {
    case UnscaledNarrowOop:
      return "32-bits Oops";
    case ZeroBasedNarrowOop:
      return "zero based Compressed Oops";
    case HeapBasedNarrowOop:

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