1 /*
   2  * Copyright (c) 2001, 2017, 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 static long getSeed() {
  69       return (long) seedField.getValue();
  70   }
  71 
  72   public static boolean useAlternateHashcode() {
  73       if (getSeed() != 0) {
  74           return true;
  75       }
  76       return false;
  77   }
  78 
  79   public SymbolTable(Address addr) {
  80     super(addr);
  81   }
  82 
  83   /** Clone of VM's "temporary" probe routine, as the SA currently
  84       does not support mutation so lookup() would have no effect
  85       anyway. Returns null if the given string is not in the symbol
  86       table. */
  87   public Symbol probe(String name) {
  88     try {
  89       return probe(toModifiedUTF8Bytes(name));
  90     } catch (IOException e) {
  91       return null;
  92     }
  93   }
  94 
  95   /** Clone of VM's "temporary" probe routine, as the SA currently
  96       does not support mutation so lookup() would have no effect
  97       anyway. Searches the regular symbol table and the shared symbol
  98       table. Null is returned if the given name is not found in both
  99       tables. */
 100   public Symbol probe(byte[] name) {
 101     long hashValue = hashSymbol(name);
 102 
 103     // shared table does not use alternate hashing algorithm,
 104     // it always uses the same original hash code.
 105     Symbol s = sharedTable.probe(name, hashValue);
 106     if (s != null) {
 107       return s;
 108     }
 109 
 110     if (useAlternateHashcode()) {
 111         hashValue = AltHashing.murmur3_32(getSeed(), name);
 112     }
 113 
 114     for (HashtableEntry e = (HashtableEntry) bucket(hashToIndex(hashValue)); e != null; e = (HashtableEntry) e.next()) {
 115       if (e.hash() == hashValue) {
 116          Symbol sym = Symbol.create(e.literalValue());
 117          if (sym.equals(name)) {
 118            return sym;
 119          }
 120       }
 121     }
 122 
 123     return null;
 124   }
 125 
 126   public interface SymbolVisitor {
 127     public void visit(Symbol sym);
 128   }
 129 
 130   public void symbolsDo(SymbolVisitor visitor) {
 131     int numBuckets = tableSize();
 132     for (int i = 0; i < numBuckets; i++) {
 133       for (HashtableEntry e = (HashtableEntry) bucket(i); e != null;
 134            e = (HashtableEntry) e.next()) {
 135         visitor.visit(Symbol.create(e.literalValue()));
 136       }
 137     }
 138   }
 139 
 140   private static byte[] toModifiedUTF8Bytes(String name) throws IOException {
 141     ByteArrayOutputStream baos = new ByteArrayOutputStream();
 142     DataOutputStream dos = new DataOutputStream(baos);
 143     dos.writeUTF(name);
 144     dos.flush();
 145     byte[] buf = baos.toByteArray();
 146     byte[] res = new byte[buf.length - 2];
 147     // skip the length part
 148     System.arraycopy(buf, 2, res, 0, res.length);
 149     return res;
 150   }
 151 }