1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 package sun.jvm.hotspot.memory;
  26 
  27 import java.io.*;
  28 import java.util.*;
  29 import sun.jvm.hotspot.debugger.*;
  30 import sun.jvm.hotspot.oops.*;
  31 import sun.jvm.hotspot.types.*;
  32 import sun.jvm.hotspot.runtime.*;
  33 import sun.jvm.hotspot.utilities.*;
  34 
  35 public class SymbolTable extends sun.jvm.hotspot.utilities.Hashtable {
  36   static {
  37     VM.registerVMInitializedObserver(new Observer() {
  38         public void update(Observable o, Object data) {
  39           initialize(VM.getVM().getTypeDataBase());
  40         }
  41       });
  42   }
  43 
  44   private static synchronized void initialize(TypeDataBase db) {
  45     Type type = db.lookupType("SymbolTable");
  46     theTableField  = type.getAddressField("_the_table");
  47     sharedTableField = type.getAddressField("_shared_table");
  48     type = db.lookupType("RehashableSymbolHashtable");
  49     seedField = type.getCIntegerField("_seed");
  50   }
  51 
  52   // Fields
  53   private static AddressField theTableField;
  54   private static AddressField sharedTableField;
  55   private static CIntegerField seedField;
  56 
  57   private CompactHashTable sharedTable;
  58 
  59   // Accessors
  60   public static SymbolTable getTheTable() {
  61     Address tmp = theTableField.getValue();
  62     SymbolTable table = (SymbolTable) VMObjectFactory.newObject(SymbolTable.class, tmp);
  63     Address shared = sharedTableField.getStaticFieldAddress();
  64     table.sharedTable = (CompactHashTable)VMObjectFactory.newObject(CompactHashTable.class, shared);
  65     return table;
  66   }
  67 
  68   public CompactHashTable getSharedTable() {
  69       return sharedTable;
  70   }
  71 
  72   public static long getSeed() {
  73       return (long) seedField.getValue();
  74   }
  75 
  76   public static boolean useAlternateHashcode() {
  77       if (getSeed() != 0) {
  78           return true;
  79       }
  80       return false;
  81   }
  82 
  83   public SymbolTable(Address addr) {
  84     super(addr);
  85   }
  86 
  87   /** Clone of VM's "temporary" probe routine, as the SA currently
  88       does not support mutation so lookup() would have no effect
  89       anyway. Returns null if the given string is not in the symbol
  90       table. */
  91   public Symbol probe(String name) {
  92     try {
  93       return probe(toModifiedUTF8Bytes(name));
  94     } catch (IOException e) {
  95       return null;
  96     }
  97   }
  98 
  99   /** Clone of VM's "temporary" probe routine, as the SA currently
 100       does not support mutation so lookup() would have no effect
 101       anyway. Searches the regular symbol table and the shared symbol
 102       table. Null is returned if the given name is not found in both
 103       tables. */
 104   public Symbol probe(byte[] name) {
 105     long hashValue = hashSymbol(name);
 106 
 107     // shared table does not use alternate hashing algorithm,
 108     // it always uses the same original hash code.
 109     Symbol s = sharedTable.probe(name, hashValue);
 110     if (s != null) {
 111       return s;
 112     }
 113 
 114     if (useAlternateHashcode()) {
 115         hashValue = AltHashing.murmur3_32(getSeed(), name);
 116     }
 117 
 118     for (HashtableEntry e = (HashtableEntry) bucket(hashToIndex(hashValue)); e != null; e = (HashtableEntry) e.next()) {
 119       if (e.hash() == hashValue) {
 120          Symbol sym = Symbol.create(e.literalValue());
 121          if (sym.equals(name)) {
 122            return sym;
 123          }
 124       }
 125     }
 126 
 127     return null;
 128   }
 129 
 130   public interface SymbolVisitor {
 131     public void visit(Symbol sym);
 132   }
 133 
 134   public void symbolsDo(SymbolVisitor visitor) {
 135     int numBuckets = tableSize();
 136     for (int i = 0; i < numBuckets; i++) {
 137       for (HashtableEntry e = (HashtableEntry) bucket(i); e != null;
 138            e = (HashtableEntry) e.next()) {
 139         visitor.visit(Symbol.create(e.literalValue()));
 140       }
 141     }
 142   }
 143 
 144   private static byte[] toModifiedUTF8Bytes(String name) throws IOException {
 145     ByteArrayOutputStream baos = new ByteArrayOutputStream();
 146     DataOutputStream dos = new DataOutputStream(baos);
 147     dos.writeUTF(name);
 148     dos.flush();
 149     byte[] buf = baos.toByteArray();
 150     byte[] res = new byte[buf.length - 2];
 151     // skip the length part
 152     System.arraycopy(buf, 2, res, 0, res.length);
 153     return res;
 154   }
 155 }