hotspot/agent/src/share/classes/sun/jvm/hotspot/oops/Symbol.java
author coleenp
Thu, 27 Jan 2011 16:11:27 -0800
changeset 8076 96d498ec7ae1
parent 5547 f4b087cbb361
child 8921 14bfe81f2a9d
permissions -rw-r--r--
6990754: Use native memory and reference counting to implement SymbolTable Summary: move symbols from permgen into C heap and reference count them Reviewed-by: never, acorn, jmasa, stefank
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/*
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 * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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package sun.jvm.hotspot.oops;
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import java.io.*;
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import java.util.*;
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import sun.jvm.hotspot.debugger.*;
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import sun.jvm.hotspot.runtime.*;
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import sun.jvm.hotspot.types.*;
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import sun.jvm.hotspot.utilities.*;
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// A Symbol is a canonicalized string.
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// All Symbols reside in global symbolTable.
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public class Symbol extends VMObject {
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  static {
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    VM.registerVMInitializedObserver(new Observer() {
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        public void update(Observable o, Object data) {
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          initialize(VM.getVM().getTypeDataBase());
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        }
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      });
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  }
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  private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
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    Type type  = db.lookupType("Symbol");
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    length     = type.getCIntegerField("_length");
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    baseOffset = type.getField("_body").getOffset();
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    idHash = type.getCIntegerField("_identity_hash");
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  }
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  // Format:
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  //   [header]
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  //   [klass ]
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  //   [length] byte size of uft8 string
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  //   ..body..
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  public static Symbol create(Address addr) {
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    if (addr == null) {
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      return null;
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    }
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    return new Symbol(addr);
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  }
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  Symbol(Address addr) {
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    super(addr);
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  }
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  public boolean isSymbol()            { return true; }
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  private static long baseOffset; // tells where the array part starts
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  // Fields
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  private static CIntegerField length;
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  // Accessors for declared fields
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  public long   getLength() { return          length.getValue(this.addr); }
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  public byte getByteAt(long index) {
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    return addr.getJByteAt(baseOffset + index);
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  }
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  private static CIntegerField idHash;
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  public int identityHash() { return     (int)idHash.getValue(this.addr); }
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  public boolean equals(byte[] modUTF8Chars) {
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    int l = (int) getLength();
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    if (l != modUTF8Chars.length) return false;
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    while (l-- > 0) {
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      if (modUTF8Chars[l] != getByteAt(l)) return false;
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    }
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    if (Assert.ASSERTS_ENABLED) {
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      Assert.that(l == -1, "we should be at the beginning");
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    }
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    return true;
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  }
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  public byte[] asByteArray() {
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    int length = (int) getLength();
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    byte [] result = new byte [length];
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    for (int index = 0; index < length; index++) {
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      result[index] = getByteAt(index);
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    }
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    return result;
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  }
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  public String asString() {
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    // Decode the byte array and return the string.
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    try {
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      return readModifiedUTF8(asByteArray());
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    } catch(Exception e) {
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      System.err.println(addr);
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      e.printStackTrace();
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      return null;
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    }
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  }
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  public boolean startsWith(String str) {
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    return asString().startsWith(str);
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  }
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  public void printValueOn(PrintStream tty) {
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    tty.print("#" + asString());
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  }
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  /** Note: this comparison is used for vtable sorting only; it
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      doesn't matter what order it defines, as long as it is a total,
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      time-invariant order Since Symbol* are in C_HEAP, their
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      relative order in memory never changes, so use address
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      comparison for speed. */
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  public int fastCompare(Symbol other) {
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    return (int) addr.minus(other.addr);
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  }
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  private static String readModifiedUTF8(byte[] buf) throws IOException {
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    final int len = buf.length;
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    byte[] tmp = new byte[len + 2];
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    // write modified UTF-8 length as short in big endian
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    tmp[0] = (byte) ((len >>> 8) & 0xFF);
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    tmp[1] = (byte) ((len >>> 0) & 0xFF);
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    // copy the data
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    System.arraycopy(buf, 0, tmp, 2, len);
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    DataInputStream dis = new DataInputStream(new ByteArrayInputStream(tmp));
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    return dis.readUTF();
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  }
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}