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 }