1 /*

     2  * Copyright (c) 1997, 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 #ifndef SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP

    26 #define SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP

    27 

    28 #include "memory/allocation.inline.hpp"

    29 #include "oops/symbol.hpp"

    30 #include "utilities/hashtable.hpp"

    31 

    32 // The symbol table holds all Symbol*s and corresponding interned strings.

    33 // Symbol*s and literal strings should be canonicalized.

    34 //

    35 // The interned strings are created lazily.

    36 //

    37 // It is implemented as an open hash table with a fixed number of buckets.

    38 //

    39 // %note:

    40 //  - symbolTableEntrys are allocated in blocks to reduce the space overhead.

    41 

    42 class BoolObjectClosure;

    43 class outputStream;

    44 class SerializeClosure;

    45 

    46 // TempNewSymbol acts as a handle class in a handle/body idiom and is

    47 // responsible for proper resource management of the body (which is a Symbol*).

    48 // The body is resource managed by a reference counting scheme.

    49 // TempNewSymbol can therefore be used to properly hold a newly created or referenced

    50 // Symbol* temporarily in scope.

    51 //

    52 // Routines in SymbolTable will initialize the reference count of a Symbol* before

    53 // it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol

    54 // needs to maintain proper reference counting in context of copy semantics.

    55 //

    56 // In SymbolTable, new_symbol() and lookup() will create a Symbol* if not already in the

    57 // symbol table and add to the symbol's reference count.

    58 // probe() and lookup_only() will increment the refcount if symbol is found.

    59 class TempNewSymbol : public StackObj {

    60   Symbol* _temp;

    61 

    62  public:

    63   TempNewSymbol() : _temp(NULL) {}

    64 

    65   // Conversion from a Symbol* to a TempNewSymbol.

    66   // Does not increment the current reference count.

    67   TempNewSymbol(Symbol *s) : _temp(s) {}

    68 

    69   // Copy constructor increments reference count.

    70   TempNewSymbol(const TempNewSymbol& rhs) : _temp(rhs._temp) {

    71     if (_temp != NULL) {

    72       _temp->increment_refcount();

    73     }

    74   }

    75 

    76   // Assignment operator uses a c++ trick called copy and swap idiom.

    77   // rhs is passed by value so within the scope of this method it is a copy.

    78   // At method exit it contains the former value of _temp, triggering the correct refcount

    79   // decrement upon destruction.

    80   void operator=(TempNewSymbol rhs) {

    81     Symbol* tmp = rhs._temp;

    82     rhs._temp = _temp;

    83     _temp = tmp;

    84   }

    85 

    86   // Decrement reference counter so it can go away if it's unused

    87   ~TempNewSymbol() {

    88     if (_temp != NULL) {

    89       _temp->decrement_refcount();

    90     }

    91   }

    92 

    93   // Symbol* conversion operators

    94   Symbol* operator -> () const                   { return _temp; }

    95   bool    operator == (Symbol* o) const          { return _temp == o; }

    96   operator Symbol*()                             { return _temp; }

    97 };

    98 

    99 template <class T, class N> class CompactHashtable;

   100 

   101 class SymbolTable : public RehashableHashtable<Symbol*, mtSymbol> {

   102   friend class VMStructs;

   103   friend class ClassFileParser;

   104 

   105 private:

   106   // The symbol table

   107   static SymbolTable* _the_table;

   108 

   109   // Set if one bucket is out of balance due to hash algorithm deficiency

   110   static bool _needs_rehashing;

   111   static bool _lookup_shared_first;

   112 

   113   // For statistics

   114   static int _symbols_removed;

   115   static int _symbols_counted;

   116 

   117   // shared symbol table.

   118   static CompactHashtable<Symbol*, char> _shared_table;

   119 

   120   Symbol* allocate_symbol(const u1* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F

   121 

   122   // Adding elements

   123   Symbol* basic_add(int index, u1* name, int len, unsigned int hashValue,

   124                     bool c_heap, TRAPS);

   125   bool basic_add(ClassLoaderData* loader_data,

   126                  const constantPoolHandle& cp, int names_count,

   127                  const char** names, int* lengths, int* cp_indices,

   128                  unsigned int* hashValues, TRAPS);

   129 

   130   static void new_symbols(ClassLoaderData* loader_data,

   131                           const constantPoolHandle& cp, int names_count,

   132                           const char** name, int* lengths,

   133                           int* cp_indices, unsigned int* hashValues,

   134                           TRAPS) {

   135     add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);

   136   }

   137 

   138   static Symbol* lookup_shared(const char* name, int len, unsigned int hash);

   139   Symbol* lookup_dynamic(int index, const char* name, int len, unsigned int hash);

   140   Symbol* lookup(int index, const char* name, int len, unsigned int hash);

   141 

   142   SymbolTable()

   143     : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}

   144 

   145   SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)

   146     : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,

   147                 number_of_entries) {}

   148 

   149   // Arena for permanent symbols (null class loader) that are never unloaded

   150   static Arena*  _arena;

   151   static Arena* arena() { return _arena; }  // called for statistics

   152 

   153   static void initialize_symbols(int arena_alloc_size = 0);

   154 

   155   static volatile int _parallel_claimed_idx;

   156 

   157   typedef SymbolTable::BucketUnlinkContext BucketUnlinkContext;

   158   // Release any dead symbols. Unlinked bucket entries are collected in the given

   159   // context to be freed later.

   160   // This allows multiple threads to work on the table at once.

   161   static void buckets_unlink(int start_idx, int end_idx, BucketUnlinkContext* context);

   162 public:

   163   enum {

   164     symbol_alloc_batch_size = 8,

   165     // Pick initial size based on java -version size measurements

   166     symbol_alloc_arena_size = 360*K

   167   };

   168 

   169   // The symbol table

   170   static SymbolTable* the_table() { return _the_table; }

   171 

   172   // Size of one bucket in the string table.  Used when checking for rollover.

   173   static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }

   174 

   175   static void create_table() {

   176     assert(_the_table == NULL, "One symbol table allowed.");

   177     _the_table = new SymbolTable();

   178     initialize_symbols(symbol_alloc_arena_size);

   179   }

   180 

   181   static unsigned int hash_symbol(const char* s, int len);

   182   static unsigned int hash_shared_symbol(const char* s, int len);

   183 

   184   static Symbol* lookup(const char* name, int len, TRAPS);

   185   // lookup only, won't add. Also calculate hash.

   186   static Symbol* lookup_only(const char* name, int len, unsigned int& hash);

   187   // Only copy to C string to be added if lookup failed.

   188   static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);

   189 

   190   static void release(Symbol* sym);

   191 

   192   // Look up the address of the literal in the SymbolTable for this Symbol*

   193   static Symbol** lookup_symbol_addr(Symbol* sym);

   194 

   195   // jchar (UTF16) version of lookups

   196   static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);

   197   static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);

   198 

   199   static void add(ClassLoaderData* loader_data,

   200                   const constantPoolHandle& cp, int names_count,

   201                   const char** names, int* lengths, int* cp_indices,

   202                   unsigned int* hashValues, TRAPS);

   203 

   204   // Release any dead symbols

   205   static void unlink() {

   206     int processed = 0;

   207     int removed = 0;

   208     unlink(&processed, &removed);

   209   }

   210   static void unlink(int* processed, int* removed);

   211   // Release any dead symbols, possibly parallel version

   212   static void possibly_parallel_unlink(int* processed, int* removed);

   213 

   214   // iterate over symbols

   215   static void symbols_do(SymbolClosure *cl);

   216   static void metaspace_pointers_do(MetaspaceClosure* it);

   217 

   218   // Symbol creation

   219   static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {

   220     assert(utf8_buffer != NULL, "just checking");

   221     return lookup(utf8_buffer, length, THREAD);

   222   }

   223   static Symbol*       new_symbol(const char* name, TRAPS) {

   224     return new_symbol(name, (int)strlen(name), THREAD);

   225   }

   226   static Symbol*       new_symbol(const Symbol* sym, int begin, int end, TRAPS) {

   227     assert(begin <= end && end <= sym->utf8_length(), "just checking");

   228     return lookup(sym, begin, end, THREAD);

   229   }

   230 

   231   // Create a symbol in the arena for symbols that are not deleted

   232   static Symbol* new_permanent_symbol(const char* name, TRAPS);

   233 

   234   // Symbol lookup

   235   static Symbol* lookup(int index, const char* name, int len, TRAPS);

   236 

   237   // Needed for preloading classes in signatures when compiling.

   238   // Returns the symbol is already present in symbol table, otherwise

   239   // NULL.  NO ALLOCATION IS GUARANTEED!

   240   static Symbol* probe(const char* name, int len) {

   241     unsigned int ignore_hash;

   242     return lookup_only(name, len, ignore_hash);

   243   }

   244   static Symbol* probe_unicode(const jchar* name, int len) {

   245     unsigned int ignore_hash;

   246     return lookup_only_unicode(name, len, ignore_hash);

   247   }

   248 

   249   // Histogram

   250   static void print_histogram()     PRODUCT_RETURN;

   251   static void print()     PRODUCT_RETURN;

   252 

   253   // Debugging

   254   static void verify();

   255   static void dump(outputStream* st, bool verbose=false);

   256   static void read(const char* filename, TRAPS);

   257 

   258   // Sharing

   259   static void write_to_archive();

   260   static void serialize(SerializeClosure* soc);

   261   static u4 encode_shared(Symbol* sym);

   262   static Symbol* decode_shared(u4 offset);

   263 

   264   // Rehash the symbol table if it gets out of balance

   265   static void rehash_table();

   266   static bool needs_rehashing()         { return _needs_rehashing; }

   267   // Parallel chunked scanning

   268   static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }

   269   static int parallel_claimed_index()        { return _parallel_claimed_idx; }

   270 };

   271 

   272 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP