java_lang_Class.java

/*
 * Copyright (c) 2011, 2016, 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 java.util.*;

import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.memory.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.types.AddressField;
import sun.jvm.hotspot.types.Type;
import sun.jvm.hotspot.types.TypeDataBase;
import sun.jvm.hotspot.utilities.*;

/** A utility class encapsulating useful oop operations */

// initialize fields for java.lang.Class
public class java_lang_Class {

  // java.lang.Class fields
  static int klassOffset;
  static IntField oopSizeField;

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

  private static synchronized void initialize(TypeDataBase db) {
    // klass and oop_size are HotSpot magic fields and hence we can't
    // find them from InstanceKlass for java.lang.Class.
    Type jlc = db.lookupType("java_lang_Class");
    klassOffset = (int) jlc.getCIntegerField("_klass_offset").getValue();
    int oopSizeOffset = (int) jlc.getCIntegerField("_oop_size_offset").getValue();
    oopSizeField = new IntField(new NamedFieldIdentifier("oop_size"), oopSizeOffset, true);
  }

  /** get Klass* field at offset hc_klass_offset from a java.lang.Class object */
  public static Klass asKlass(Oop aClass) {
    return (Klass)Metadata.instantiateWrapperFor(aClass.getHandle().getAddressAt(klassOffset));
  }

  /** get oop_size field at offset oop_size_offset from a java.lang.Class object */
  public static long getOopSize(Oop aClass) {
    return java_lang_Class.oopSizeField.getValue(aClass);
  }
}