       1 /*
       2  * Copyright (c) 1997, 2014, 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 #include "precompiled.hpp"
      26 #include "classfile/altHashing.hpp"
      27 #include "classfile/javaClasses.hpp"
      28 #include "classfile/symbolTable.hpp"
      29 #include "classfile/systemDictionary.hpp"
      30 #include "gc_interface/collectedHeap.inline.hpp"
      31 #include "memory/allocation.inline.hpp"
      32 #include "memory/filemap.hpp"
      33 #include "memory/gcLocker.inline.hpp"
      34 #include "oops/oop.inline.hpp"
      35 #include "oops/oop.inline2.hpp"
      36 #include "runtime/mutexLocker.hpp"
      37 #include "utilities/hashtable.inline.hpp"
      38 #if INCLUDE_ALL_GCS
      39 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
      40 #include "gc_implementation/g1/g1StringDedup.hpp"
      41 #endif
      42
      43 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
      44
      45 // --------------------------------------------------------------------------
      46
      47 // the number of buckets a thread claims
      48 const int ClaimChunkSize = 32;
      49
      50 SymbolTable* SymbolTable::_the_table = NULL;
      51 // Static arena for symbols that are not deallocated
      52 Arena* SymbolTable::_arena = NULL;
      53 bool SymbolTable::_needs_rehashing = false;
      54
      55 Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) {
      56   assert (len <= Symbol::max_length(), "should be checked by caller");
      57
      58   Symbol* sym;
      59
      60   if (DumpSharedSpaces) {
      61     // Allocate all symbols to CLD shared metaspace
      62     sym = new (len, ClassLoaderData::the_null_class_loader_data(), THREAD) Symbol(name, len, -1);
      63   } else if (c_heap) {
      64     // refcount starts as 1
      65     sym = new (len, THREAD) Symbol(name, len, 1);
      66     assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
      67   } else {
      68     // Allocate to global arena
      69     sym = new (len, arena(), THREAD) Symbol(name, len, -1);
      70   }
      71   return sym;
      72 }
      73
      74 void SymbolTable::initialize_symbols(int arena_alloc_size) {
      75   // Initialize the arena for global symbols, size passed in depends on CDS.
      76   if (arena_alloc_size == 0) {
      77     _arena = new (mtSymbol) Arena(mtSymbol);
      78   } else {
      79     _arena = new (mtSymbol) Arena(mtSymbol, arena_alloc_size);
      80   }
      81 }
      82
      83 // Call function for all symbols in the symbol table.
      84 void SymbolTable::symbols_do(SymbolClosure *cl) {
      85   const int n = the_table()->table_size();
      86   for (int i = 0; i < n; i++) {
      87     for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
      88          p != NULL;
      89          p = p->next()) {
      90       cl->do_symbol(p->literal_addr());
      91     }
      92   }
      93 }
      94
      95 int SymbolTable::_symbols_removed = 0;
      96 int SymbolTable::_symbols_counted = 0;
      97 volatile int SymbolTable::_parallel_claimed_idx = 0;
      98
      99 void SymbolTable::buckets_unlink(int start_idx, int end_idx, int* processed, int* removed, size_t* memory_total) {
     100   for (int i = start_idx; i < end_idx; ++i) {
     101     HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
     102     HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
     103     while (entry != NULL) {
     104       // Shared entries are normally at the end of the bucket and if we run into
     105       // a shared entry, then there is nothing more to remove. However, if we
     106       // have rehashed the table, then the shared entries are no longer at the
     107       // end of the bucket.
     108       if (entry->is_shared() && !use_alternate_hashcode()) {
     109         break;
     110       }
     111       Symbol* s = entry->literal();
     112       (*memory_total) += s->size();
     113       (*processed)++;
     114       assert(s != NULL, "just checking");
     115       // If reference count is zero, remove.
     116       if (s->refcount() == 0) {
     117         assert(!entry->is_shared(), "shared entries should be kept live");
     118         delete s;
     119         (*removed)++;
     120         *p = entry->next();
     121         the_table()->free_entry(entry);
     122       } else {
     123         p = entry->next_addr();
     124       }
     125       // get next entry
     126       entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
     127     }
     128   }
     129 }
     130
     131 // Remove unreferenced symbols from the symbol table
     132 // This is done late during GC.
     133 void SymbolTable::unlink(int* processed, int* removed) {
     134   size_t memory_total = 0;
     135   buckets_unlink(0, the_table()->table_size(), processed, removed, &memory_total);
     136   _symbols_removed += *removed;
     137   _symbols_counted += *processed;
     138   // Exclude printing for normal PrintGCDetails because people parse
     139   // this output.
     140   if (PrintGCDetails && Verbose && WizardMode) {
     141     gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", *processed,
     142                         (memory_total*HeapWordSize)/1024);
     143   }
     144 }
     145
     146 void SymbolTable::possibly_parallel_unlink(int* processed, int* removed) {
     147   const int limit = the_table()->table_size();
     148
     149   size_t memory_total = 0;
     150
     151   for (;;) {
     152     // Grab next set of buckets to scan
     153     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
     154     if (start_idx >= limit) {
     155       // End of table
     156       break;
     157     }
     158
     159     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
     160     buckets_unlink(start_idx, end_idx, processed, removed, &memory_total);
     161   }
     162   Atomic::add(*processed, &_symbols_counted);
     163   Atomic::add(*removed, &_symbols_removed);
     164   // Exclude printing for normal PrintGCDetails because people parse
     165   // this output.
     166   if (PrintGCDetails && Verbose && WizardMode) {
     167     gclog_or_tty->print(" [Symbols: scanned=%d removed=%d size=" SIZE_FORMAT "K] ", *processed, *removed,
     168                         (memory_total*HeapWordSize)/1024);
     169   }
     170 }
     171
     172 // Create a new table and using alternate hash code, populate the new table
     173 // with the existing strings.   Set flag to use the alternate hash code afterwards.
     174 void SymbolTable::rehash_table() {
     175   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
     176   // This should never happen with -Xshare:dump but it might in testing mode.
     177   if (DumpSharedSpaces) return;
     178   // Create a new symbol table
     179   SymbolTable* new_table = new SymbolTable();
     180
     181   the_table()->move_to(new_table);
     182
     183   // Delete the table and buckets (entries are reused in new table).
     184   delete _the_table;
     185   // Don't check if we need rehashing until the table gets unbalanced again.
     186   // Then rehash with a new global seed.
     187   _needs_rehashing = false;
     188   _the_table = new_table;
     189 }
     190
     191 // Lookup a symbol in a bucket.
     192
     193 Symbol* SymbolTable::lookup(int index, const char* name,
     194                               int len, unsigned int hash) {
     195   int count = 0;
     196   for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {
     197     count++;  // count all entries in this bucket, not just ones with same hash
     198     if (e->hash() == hash) {
     199       Symbol* sym = e->literal();
     200       if (sym->equals(name, len)) {
     201         // something is referencing this symbol now.
     202         sym->increment_refcount();
     203         return sym;
     204       }
     205     }
     206   }
     207   // If the bucket size is too deep check if this hash code is insufficient.
     208   if (count >= rehash_count && !needs_rehashing()) {
     209     _needs_rehashing = check_rehash_table(count);
     210   }
     211   return NULL;
     212 }
     213
     214 // Pick hashing algorithm.
     215 unsigned int SymbolTable::hash_symbol(const char* s, int len) {
     216   return use_alternate_hashcode() ?
     217            AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :
     218            java_lang_String::hash_code(s, len);
     219 }
     220
     221
     222 // We take care not to be blocking while holding the
     223 // SymbolTable_lock. Otherwise, the system might deadlock, since the
     224 // symboltable is used during compilation (VM_thread) The lock free
     225 // synchronization is simplified by the fact that we do not delete
     226 // entries in the symbol table during normal execution (only during
     227 // safepoints).
     228
     229 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
     230   unsigned int hashValue = hash_symbol(name, len);
     231   int index = the_table()->hash_to_index(hashValue);
     232
     233   Symbol* s = the_table()->lookup(index, name, len, hashValue);
     234
     235   // Found
     236   if (s != NULL) return s;
     237
     238   // Grab SymbolTable_lock first.
     239   MutexLocker ml(SymbolTable_lock, THREAD);
     240
     241   // Otherwise, add to symbol to table
     242   return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);
     243 }
     244
     245 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
     246   char* buffer;
     247   int index, len;
     248   unsigned int hashValue;
     249   char* name;
     250   {
     251     debug_only(No_Safepoint_Verifier nsv;)
     252
     253     name = (char*)sym->base() + begin;
     254     len = end - begin;
     255     hashValue = hash_symbol(name, len);
     256     index = the_table()->hash_to_index(hashValue);
     257     Symbol* s = the_table()->lookup(index, name, len, hashValue);
     258
     259     // Found
     260     if (s != NULL) return s;
     261   }
     262
     263   // Otherwise, add to symbol to table. Copy to a C string first.
     264   char stack_buf[128];
     265   ResourceMark rm(THREAD);
     266   if (len <= 128) {
     267     buffer = stack_buf;
     268   } else {
     269     buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
     270   }
     271   for (int i=0; i<len; i++) {
     272     buffer[i] = name[i];
     273   }
     274   // Make sure there is no safepoint in the code above since name can't move.
     275   // We can't include the code in No_Safepoint_Verifier because of the
     276   // ResourceMark.
     277
     278   // Grab SymbolTable_lock first.
     279   MutexLocker ml(SymbolTable_lock, THREAD);
     280
     281   return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);
     282 }
     283
     284 Symbol* SymbolTable::lookup_only(const char* name, int len,
     285                                    unsigned int& hash) {
     286   hash = hash_symbol(name, len);
     287   int index = the_table()->hash_to_index(hash);
     288
     289   Symbol* s = the_table()->lookup(index, name, len, hash);
     290   return s;
     291 }
     292
     293 // Look up the address of the literal in the SymbolTable for this Symbol*
     294 // Do not create any new symbols
     295 // Do not increment the reference count to keep this alive
     296 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){
     297   unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());
     298   int index = the_table()->hash_to_index(hash);
     299
     300   for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {
     301     if (e->hash() == hash) {
     302       Symbol* literal_sym = e->literal();
     303       if (sym == literal_sym) {
     304         return e->literal_addr();
     305       }
     306     }
     307   }
     308   return NULL;
     309 }
     310
     311 // Suggestion: Push unicode-based lookup all the way into the hashing
     312 // and probing logic, so there is no need for convert_to_utf8 until
     313 // an actual new Symbol* is created.
     314 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
     315   int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
     316   char stack_buf[128];
     317   if (utf8_length < (int) sizeof(stack_buf)) {
     318     char* chars = stack_buf;
     319     UNICODE::convert_to_utf8(name, utf16_length, chars);
     320     return lookup(chars, utf8_length, THREAD);
     321   } else {
     322     ResourceMark rm(THREAD);
     323     char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
     324     UNICODE::convert_to_utf8(name, utf16_length, chars);
     325     return lookup(chars, utf8_length, THREAD);
     326   }
     327 }
     328
     329 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
     330                                            unsigned int& hash) {
     331   int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
     332   char stack_buf[128];
     333   if (utf8_length < (int) sizeof(stack_buf)) {
     334     char* chars = stack_buf;
     335     UNICODE::convert_to_utf8(name, utf16_length, chars);
     336     return lookup_only(chars, utf8_length, hash);
     337   } else {
     338     ResourceMark rm;
     339     char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
     340     UNICODE::convert_to_utf8(name, utf16_length, chars);
     341     return lookup_only(chars, utf8_length, hash);
     342   }
     343 }
     344
     345 void SymbolTable::add(ClassLoaderData* loader_data, constantPoolHandle cp,
     346                       int names_count,
     347                       const char** names, int* lengths, int* cp_indices,
     348                       unsigned int* hashValues, TRAPS) {
     349   // Grab SymbolTable_lock first.
     350   MutexLocker ml(SymbolTable_lock, THREAD);
     351
     352   SymbolTable* table = the_table();
     353   bool added = table->basic_add(loader_data, cp, names_count, names, lengths,
     354                                 cp_indices, hashValues, CHECK);
     355   if (!added) {
     356     // do it the hard way
     357     for (int i=0; i<names_count; i++) {
     358       int index = table->hash_to_index(hashValues[i]);
     359       bool c_heap = !loader_data->is_the_null_class_loader_data();
     360       Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);
     361       cp->symbol_at_put(cp_indices[i], sym);
     362     }
     363   }
     364 }
     365
     366 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
     367   unsigned int hash;
     368   Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);
     369   if (result != NULL) {
     370     return result;
     371   }
     372   // Grab SymbolTable_lock first.
     373   MutexLocker ml(SymbolTable_lock, THREAD);
     374
     375   SymbolTable* table = the_table();
     376   int index = table->hash_to_index(hash);
     377   return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);
     378 }
     379
     380 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,
     381                                unsigned int hashValue_arg, bool c_heap, TRAPS) {
     382   assert(!Universe::heap()->is_in_reserved(name),
     383          "proposed name of symbol must be stable");
     384
     385   // Don't allow symbols to be created which cannot fit in a Symbol*.
     386   if (len > Symbol::max_length()) {
     387     THROW_MSG_0(vmSymbols::java_lang_InternalError(),
     388                 "name is too long to represent");
     389   }
     390
     391   // Cannot hit a safepoint in this function because the "this" pointer can move.
     392   No_Safepoint_Verifier nsv;
     393
     394   // Check if the symbol table has been rehashed, if so, need to recalculate
     395   // the hash value and index.
     396   unsigned int hashValue;
     397   int index;
     398   if (use_alternate_hashcode()) {
     399     hashValue = hash_symbol((const char*)name, len);
     400     index = hash_to_index(hashValue);
     401   } else {
     402     hashValue = hashValue_arg;
     403     index = index_arg;
     404   }
     405
     406   // Since look-up was done lock-free, we need to check if another
     407   // thread beat us in the race to insert the symbol.
     408   Symbol* test = lookup(index, (char*)name, len, hashValue);
     409   if (test != NULL) {
     410     // A race occurred and another thread introduced the symbol.
     411     assert(test->refcount() != 0, "lookup should have incremented the count");
     412     return test;
     413   }
     414
     415   // Create a new symbol.
     416   Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);
     417   assert(sym->equals((char*)name, len), "symbol must be properly initialized");
     418
     419   HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
     420   add_entry(index, entry);
     421   return sym;
     422 }
     423
     424 // This version of basic_add adds symbols in batch from the constant pool
     425 // parsing.
     426 bool SymbolTable::basic_add(ClassLoaderData* loader_data, constantPoolHandle cp,
     427                             int names_count,
     428                             const char** names, int* lengths,
     429                             int* cp_indices, unsigned int* hashValues,
     430                             TRAPS) {
     431
     432   // Check symbol names are not too long.  If any are too long, don't add any.
     433   for (int i = 0; i< names_count; i++) {
     434     if (lengths[i] > Symbol::max_length()) {
     435       THROW_MSG_0(vmSymbols::java_lang_InternalError(),
     436                   "name is too long to represent");
     437     }
     438   }
     439
     440   // Cannot hit a safepoint in this function because the "this" pointer can move.
     441   No_Safepoint_Verifier nsv;
     442
     443   for (int i=0; i<names_count; i++) {
     444     // Check if the symbol table has been rehashed, if so, need to recalculate
     445     // the hash value.
     446     unsigned int hashValue;
     447     if (use_alternate_hashcode()) {
     448       hashValue = hash_symbol(names[i], lengths[i]);
     449     } else {
     450       hashValue = hashValues[i];
     451     }
     452     // Since look-up was done lock-free, we need to check if another
     453     // thread beat us in the race to insert the symbol.
     454     int index = hash_to_index(hashValue);
     455     Symbol* test = lookup(index, names[i], lengths[i], hashValue);
     456     if (test != NULL) {
     457       // A race occurred and another thread introduced the symbol, this one
     458       // will be dropped and collected. Use test instead.
     459       cp->symbol_at_put(cp_indices[i], test);
     460       assert(test->refcount() != 0, "lookup should have incremented the count");
     461     } else {
     462       // Create a new symbol.  The null class loader is never unloaded so these
     463       // are allocated specially in a permanent arena.
     464       bool c_heap = !loader_data->is_the_null_class_loader_data();
     465       Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));
     466       assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized");  // why wouldn't it be???
     467       HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
     468       add_entry(index, entry);
     469       cp->symbol_at_put(cp_indices[i], sym);
     470     }
     471   }
     472   return true;
     473 }
     474
     475
     476 void SymbolTable::verify() {
     477   for (int i = 0; i < the_table()->table_size(); ++i) {
     478     HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
     479     for ( ; p != NULL; p = p->next()) {
     480       Symbol* s = (Symbol*)(p->literal());
     481       guarantee(s != NULL, "symbol is NULL");
     482       unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
     483       guarantee(p->hash() == h, "broken hash in symbol table entry");
     484       guarantee(the_table()->hash_to_index(h) == i,
     485                 "wrong index in symbol table");
     486     }
     487   }
     488 }
     489
     490 void SymbolTable::dump(outputStream* st) {
     491   the_table()->dump_table(st, "SymbolTable");
     492 }
     493
     494
     495 //---------------------------------------------------------------------------
     496 // Non-product code
     497
     498 #ifndef PRODUCT
     499
     500 void SymbolTable::print_histogram() {
     501   MutexLocker ml(SymbolTable_lock);
     502   const int results_length = 100;
     503   int results[results_length];
     504   int i,j;
     505
     506   // initialize results to zero
     507   for (j = 0; j < results_length; j++) {
     508     results[j] = 0;
     509   }
     510
     511   int total = 0;
     512   int max_symbols = 0;
     513   int out_of_range = 0;
     514   int memory_total = 0;
     515   int count = 0;
     516   for (i = 0; i < the_table()->table_size(); i++) {
     517     HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
     518     for ( ; p != NULL; p = p->next()) {
     519       memory_total += p->literal()->size();
     520       count++;
     521       int counter = p->literal()->utf8_length();
     522       total += counter;
     523       if (counter < results_length) {
     524         results[counter]++;
     525       } else {
     526         out_of_range++;
     527       }
     528       max_symbols = MAX2(max_symbols, counter);
     529     }
     530   }
     531   tty->print_cr("Symbol Table:");
     532   tty->print_cr("Total number of symbols  %5d", count);
     533   tty->print_cr("Total size in memory     %5dK",
     534           (memory_total*HeapWordSize)/1024);
     535   tty->print_cr("Total counted            %5d", _symbols_counted);
     536   tty->print_cr("Total removed            %5d", _symbols_removed);
     537   if (_symbols_counted > 0) {
     538     tty->print_cr("Percent removed          %3.2f",
     539           ((float)_symbols_removed/(float)_symbols_counted)* 100);
     540   }
     541   tty->print_cr("Reference counts         %5d", Symbol::_total_count);
     542   tty->print_cr("Symbol arena size        %5d used %5d",
     543                  arena()->size_in_bytes(), arena()->used());
     544   tty->print_cr("Histogram of symbol length:");
     545   tty->print_cr("%8s %5d", "Total  ", total);
     546   tty->print_cr("%8s %5d", "Maximum", max_symbols);
     547   tty->print_cr("%8s %3.2f", "Average",
     548           ((float) total / (float) the_table()->table_size()));
     549   tty->print_cr("%s", "Histogram:");
     550   tty->print_cr(" %s %29s", "Length", "Number chains that length");
     551   for (i = 0; i < results_length; i++) {
     552     if (results[i] > 0) {
     553       tty->print_cr("%6d %10d", i, results[i]);
     554     }
     555   }
     556   if (Verbose) {
     557     int line_length = 70;
     558     tty->print_cr("%s %30s", " Length", "Number chains that length");
     559     for (i = 0; i < results_length; i++) {
     560       if (results[i] > 0) {
     561         tty->print("%4d", i);
     562         for (j = 0; (j < results[i]) && (j < line_length);  j++) {
     563           tty->print("%1s", "*");
     564         }
     565         if (j == line_length) {
     566           tty->print("%1s", "+");
     567         }
     568         tty->cr();
     569       }
     570     }
     571   }
     572   tty->print_cr(" %s %d: %d\n", "Number chains longer than",
     573                     results_length, out_of_range);
     574 }
     575
     576 void SymbolTable::print() {
     577   for (int i = 0; i < the_table()->table_size(); ++i) {
     578     HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
     579     HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
     580     if (entry != NULL) {
     581       while (entry != NULL) {
     582         tty->print(PTR_FORMAT " ", entry->literal());
     583         entry->literal()->print();
     584         tty->print(" %d", entry->literal()->refcount());
     585         p = entry->next_addr();
     586         entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
     587       }
     588       tty->cr();
     589     }
     590   }
     591 }
     592 #endif // PRODUCT
     593
     594 // --------------------------------------------------------------------------
     595
     596 #ifdef ASSERT
     597 class StableMemoryChecker : public StackObj {
     598   enum { _bufsize = wordSize*4 };
     599
     600   address _region;
     601   jint    _size;
     602   u1      _save_buf[_bufsize];
     603
     604   int sample(u1* save_buf) {
     605     if (_size <= _bufsize) {
     606       memcpy(save_buf, _region, _size);
     607       return _size;
     608     } else {
     609       // copy head and tail
     610       memcpy(&save_buf[0],          _region,                      _bufsize/2);
     611       memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
     612       return (_bufsize/2)*2;
     613     }
     614   }
     615
     616  public:
     617   StableMemoryChecker(const void* region, jint size) {
     618     _region = (address) region;
     619     _size   = size;
     620     sample(_save_buf);
     621   }
     622
     623   bool verify() {
     624     u1 check_buf[sizeof(_save_buf)];
     625     int check_size = sample(check_buf);
     626     return (0 == memcmp(_save_buf, check_buf, check_size));
     627   }
     628
     629   void set_region(const void* region) { _region = (address) region; }
     630 };
     631 #endif
     632
     633
     634 // --------------------------------------------------------------------------
     635 StringTable* StringTable::_the_table = NULL;
     636
     637 bool StringTable::_needs_rehashing = false;
     638
     639 volatile int StringTable::_parallel_claimed_idx = 0;
     640
     641 // Pick hashing algorithm
     642 unsigned int StringTable::hash_string(const jchar* s, int len) {
     643   return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
     644                                     java_lang_String::hash_code(s, len);
     645 }
     646
     647 oop StringTable::lookup(int index, jchar* name,
     648                         int len, unsigned int hash) {
     649   int count = 0;
     650   for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
     651     count++;
     652     if (l->hash() == hash) {
     653       if (java_lang_String::equals(l->literal(), name, len)) {
     654         return l->literal();
     655       }
     656     }
     657   }
     658   // If the bucket size is too deep check if this hash code is insufficient.
     659   if (count >= rehash_count && !needs_rehashing()) {
     660     _needs_rehashing = check_rehash_table(count);
     661   }
     662   return NULL;
     663 }
     664
     665
     666 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
     667                            int len, unsigned int hashValue_arg, TRAPS) {
     668
     669   assert(java_lang_String::equals(string(), name, len),
     670          "string must be properly initialized");
     671   // Cannot hit a safepoint in this function because the "this" pointer can move.
     672   No_Safepoint_Verifier nsv;
     673
     674   // Check if the symbol table has been rehashed, if so, need to recalculate
     675   // the hash value and index before second lookup.
     676   unsigned int hashValue;
     677   int index;
     678   if (use_alternate_hashcode()) {
     679     hashValue = hash_string(name, len);
     680     index = hash_to_index(hashValue);
     681   } else {
     682     hashValue = hashValue_arg;
     683     index = index_arg;
     684   }
     685
     686   // Since look-up was done lock-free, we need to check if another
     687   // thread beat us in the race to insert the symbol.
     688
     689   oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
     690   if (test != NULL) {
     691     // Entry already added
     692     return test;
     693   }
     694
     695   HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
     696   add_entry(index, entry);
     697   return string();
     698 }
     699
     700
     701 oop StringTable::lookup(Symbol* symbol) {
     702   ResourceMark rm;
     703   int length;
     704   jchar* chars = symbol->as_unicode(length);
     705   return lookup(chars, length);
     706 }
     707
     708 // Tell the GC that this string was looked up in the StringTable.
     709 static void ensure_string_alive(oop string) {
     710   // A lookup in the StringTable could return an object that was previously
     711   // considered dead. The SATB part of G1 needs to get notified about this
     712   // potential resurrection, otherwise the marking might not find the object.
     713 #if INCLUDE_ALL_GCS
     714   if (UseG1GC && string != NULL) {
     715     G1SATBCardTableModRefBS::enqueue(string);
     716   }
     717 #endif
     718 }
     719
     720 oop StringTable::lookup(jchar* name, int len) {
     721   unsigned int hash = hash_string(name, len);
     722   int index = the_table()->hash_to_index(hash);
     723   oop string = the_table()->lookup(index, name, len, hash);
     724
     725   ensure_string_alive(string);
     726
     727   return string;
     728 }
     729
     730
     731 oop StringTable::intern(Handle string_or_null, jchar* name,
     732                         int len, TRAPS) {
     733   unsigned int hashValue = hash_string(name, len);
     734   int index = the_table()->hash_to_index(hashValue);
     735   oop found_string = the_table()->lookup(index, name, len, hashValue);
     736
     737   // Found
     738   if (found_string != NULL) {
     739     ensure_string_alive(found_string);
     740     return found_string;
     741   }
     742
     743   debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
     744   assert(!Universe::heap()->is_in_reserved(name),
     745          "proposed name of symbol must be stable");
     746
     747   Handle string;
     748   // try to reuse the string if possible
     749   if (!string_or_null.is_null()) {
     750     string = string_or_null;
     751   } else {
     752     string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
     753   }
     754
     755 #if INCLUDE_ALL_GCS
     756   if (G1StringDedup::is_enabled()) {
     757     // Deduplicate the string before it is interned. Note that we should never
     758     // deduplicate a string after it has been interned. Doing so will counteract
     759     // compiler optimizations done on e.g. interned string literals.
     760     G1StringDedup::deduplicate(string());
     761   }
     762 #endif
     763
     764   // Grab the StringTable_lock before getting the_table() because it could
     765   // change at safepoint.
     766   oop added_or_found;
     767   {
     768     MutexLocker ml(StringTable_lock, THREAD);
     769     // Otherwise, add to symbol to table
     770     added_or_found = the_table()->basic_add(index, string, name, len,
     771                                   hashValue, CHECK_NULL);
     772   }
     773
     774   ensure_string_alive(added_or_found);
     775
     776   return added_or_found;
     777 }
     778
     779 oop StringTable::intern(Symbol* symbol, TRAPS) {
     780   if (symbol == NULL) return NULL;
     781   ResourceMark rm(THREAD);
     782   int length;
     783   jchar* chars = symbol->as_unicode(length);
     784   Handle string;
     785   oop result = intern(string, chars, length, CHECK_NULL);
     786   return result;
     787 }
     788
     789
     790 oop StringTable::intern(oop string, TRAPS)
     791 {
     792   if (string == NULL) return NULL;
     793   ResourceMark rm(THREAD);
     794   int length;
     795   Handle h_string (THREAD, string);
     796   jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
     797   oop result = intern(h_string, chars, length, CHECK_NULL);
     798   return result;
     799 }
     800
     801
     802 oop StringTable::intern(const char* utf8_string, TRAPS) {
     803   if (utf8_string == NULL) return NULL;
     804   ResourceMark rm(THREAD);
     805   int length = UTF8::unicode_length(utf8_string);
     806   jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
     807   UTF8::convert_to_unicode(utf8_string, chars, length);
     808   Handle string;
     809   oop result = intern(string, chars, length, CHECK_NULL);
     810   return result;
     811 }
     812
     813 void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
     814   buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), processed, removed);
     815 }
     816
     817 void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
     818   // Readers of the table are unlocked, so we should only be removing
     819   // entries at a safepoint.
     820   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
     821   const int limit = the_table()->table_size();
     822
     823   for (;;) {
     824     // Grab next set of buckets to scan
     825     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
     826     if (start_idx >= limit) {
     827       // End of table
     828       break;
     829     }
     830
     831     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
     832     buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, processed, removed);
     833   }
     834 }
     835
     836 void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {
     837   const int limit = the_table()->table_size();
     838
     839   assert(0 <= start_idx && start_idx <= limit,
     840          err_msg("start_idx (" INT32_FORMAT ") is out of bounds", start_idx));
     841   assert(0 <= end_idx && end_idx <= limit,
     842          err_msg("end_idx (" INT32_FORMAT ") is out of bounds", end_idx));
     843   assert(start_idx <= end_idx,
     844          err_msg("Index ordering: start_idx=" INT32_FORMAT", end_idx=" INT32_FORMAT,
     845                  start_idx, end_idx));
     846
     847   for (int i = start_idx; i < end_idx; i += 1) {
     848     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
     849     while (entry != NULL) {
     850       assert(!entry->is_shared(), "CDS not used for the StringTable");
     851
     852       f->do_oop((oop*)entry->literal_addr());
     853
     854       entry = entry->next();
     855     }
     856   }
     857 }
     858
     859 void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, int* processed, int* removed) {
     860   const int limit = the_table()->table_size();
     861
     862   assert(0 <= start_idx && start_idx <= limit,
     863          err_msg("start_idx (" INT32_FORMAT ") is out of bounds", start_idx));
     864   assert(0 <= end_idx && end_idx <= limit,
     865          err_msg("end_idx (" INT32_FORMAT ") is out of bounds", end_idx));
     866   assert(start_idx <= end_idx,
     867          err_msg("Index ordering: start_idx=" INT32_FORMAT", end_idx=" INT32_FORMAT,
     868                  start_idx, end_idx));
     869
     870   for (int i = start_idx; i < end_idx; ++i) {
     871     HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
     872     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
     873     while (entry != NULL) {
     874       assert(!entry->is_shared(), "CDS not used for the StringTable");
     875
     876       if (is_alive->do_object_b(entry->literal())) {
     877         if (f != NULL) {
     878           f->do_oop((oop*)entry->literal_addr());
     879         }
     880         p = entry->next_addr();
     881       } else {
     882         *p = entry->next();
     883         the_table()->free_entry(entry);
     884         (*removed)++;
     885       }
     886       (*processed)++;
     887       entry = *p;
     888     }
     889   }
     890 }
     891
     892 void StringTable::oops_do(OopClosure* f) {
     893   buckets_oops_do(f, 0, the_table()->table_size());
     894 }
     895
     896 void StringTable::possibly_parallel_oops_do(OopClosure* f) {
     897   const int limit = the_table()->table_size();
     898
     899   for (;;) {
     900     // Grab next set of buckets to scan
     901     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
     902     if (start_idx >= limit) {
     903       // End of table
     904       break;
     905     }
     906
     907     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
     908     buckets_oops_do(f, start_idx, end_idx);
     909   }
     910 }
     911
     912 // This verification is part of Universe::verify() and needs to be quick.
     913 // See StringTable::verify_and_compare() below for exhaustive verification.
     914 void StringTable::verify() {
     915   for (int i = 0; i < the_table()->table_size(); ++i) {
     916     HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
     917     for ( ; p != NULL; p = p->next()) {
     918       oop s = p->literal();
     919       guarantee(s != NULL, "interned string is NULL");
     920       unsigned int h = java_lang_String::hash_string(s);
     921       guarantee(p->hash() == h, "broken hash in string table entry");
     922       guarantee(the_table()->hash_to_index(h) == i,
     923                 "wrong index in string table");
     924     }
     925   }
     926 }
     927
     928 void StringTable::dump(outputStream* st) {
     929   the_table()->dump_table(st, "StringTable");
     930 }
     931
     932 StringTable::VerifyRetTypes StringTable::compare_entries(
     933                                       int bkt1, int e_cnt1,
     934                                       HashtableEntry<oop, mtSymbol>* e_ptr1,
     935                                       int bkt2, int e_cnt2,
     936                                       HashtableEntry<oop, mtSymbol>* e_ptr2) {
     937   // These entries are sanity checked by verify_and_compare_entries()
     938   // before this function is called.
     939   oop str1 = e_ptr1->literal();
     940   oop str2 = e_ptr2->literal();
     941
     942   if (str1 == str2) {
     943     tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "
     944                   "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",
     945                   (void *)str1, bkt1, e_cnt1, bkt2, e_cnt2);
     946     return _verify_fail_continue;
     947   }
     948
     949   if (java_lang_String::equals(str1, str2)) {
     950     tty->print_cr("ERROR: identical String values in entry @ "
     951                   "bucket[%d][%d] and entry @ bucket[%d][%d]",
     952                   bkt1, e_cnt1, bkt2, e_cnt2);
     953     return _verify_fail_continue;
     954   }
     955
     956   return _verify_pass;
     957 }
     958
     959 StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,
     960                                       HashtableEntry<oop, mtSymbol>* e_ptr,
     961                                       StringTable::VerifyMesgModes mesg_mode) {
     962
     963   VerifyRetTypes ret = _verify_pass;  // be optimistic
     964
     965   oop str = e_ptr->literal();
     966   if (str == NULL) {
     967     if (mesg_mode == _verify_with_mesgs) {
     968       tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,
     969                     e_cnt);
     970     }
     971     // NULL oop means no more verifications are possible
     972     return _verify_fail_done;
     973   }
     974
     975   if (str->klass() != SystemDictionary::String_klass()) {
     976     if (mesg_mode == _verify_with_mesgs) {
     977       tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",
     978                     bkt, e_cnt);
     979     }
     980     // not a String means no more verifications are possible
     981     return _verify_fail_done;
     982   }
     983
     984   unsigned int h = java_lang_String::hash_string(str);
     985   if (e_ptr->hash() != h) {
     986     if (mesg_mode == _verify_with_mesgs) {
     987       tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "
     988                     "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);
     989     }
     990     ret = _verify_fail_continue;
     991   }
     992
     993   if (the_table()->hash_to_index(h) != bkt) {
     994     if (mesg_mode == _verify_with_mesgs) {
     995       tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "
     996                     "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,
     997                     the_table()->hash_to_index(h));
     998     }
     999     ret = _verify_fail_continue;
    1000   }
    1001
    1002   return ret;
    1003 }
    1004
    1005 // See StringTable::verify() above for the quick verification that is
    1006 // part of Universe::verify(). This verification is exhaustive and
    1007 // reports on every issue that is found. StringTable::verify() only
    1008 // reports on the first issue that is found.
    1009 //
    1010 // StringTable::verify_entry() checks:
    1011 // - oop value != NULL (same as verify())
    1012 // - oop value is a String
    1013 // - hash(String) == hash in entry (same as verify())
    1014 // - index for hash == index of entry (same as verify())
    1015 //
    1016 // StringTable::compare_entries() checks:
    1017 // - oops are unique across all entries
    1018 // - String values are unique across all entries
    1019 //
    1020 int StringTable::verify_and_compare_entries() {
    1021   assert(StringTable_lock->is_locked(), "sanity check");
    1022
    1023   int  fail_cnt = 0;
    1024
    1025   // first, verify all the entries individually:
    1026   for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {
    1027     HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);
    1028     for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {
    1029       VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);
    1030       if (ret != _verify_pass) {
    1031         fail_cnt++;
    1032       }
    1033     }
    1034   }
    1035
    1036   // Optimization: if the above check did not find any failures, then
    1037   // the comparison loop below does not need to call verify_entry()
    1038   // before calling compare_entries(). If there were failures, then we
    1039   // have to call verify_entry() to see if the entry can be passed to
    1040   // compare_entries() safely. When we call verify_entry() in the loop
    1041   // below, we do so quietly to void duplicate messages and we don't
    1042   // increment fail_cnt because the failures have already been counted.
    1043   bool need_entry_verify = (fail_cnt != 0);
    1044
    1045   // second, verify all entries relative to each other:
    1046   for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {
    1047     HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);
    1048     for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {
    1049       if (need_entry_verify) {
    1050         VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,
    1051                                           _verify_quietly);
    1052         if (ret == _verify_fail_done) {
    1053           // cannot use the current entry to compare against other entries
    1054           continue;
    1055         }
    1056       }
    1057
    1058       for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {
    1059         HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);
    1060         int e_cnt2;
    1061         for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {
    1062           if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {
    1063             // skip the entries up to and including the one that
    1064             // we're comparing against
    1065             continue;
    1066           }
    1067
    1068           if (need_entry_verify) {
    1069             VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,
    1070                                               _verify_quietly);
    1071             if (ret == _verify_fail_done) {
    1072               // cannot compare against this entry
    1073               continue;
    1074             }
    1075           }
    1076
    1077           // compare two entries, report and count any failures:
    1078           if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)
    1079               != _verify_pass) {
    1080             fail_cnt++;
    1081           }
    1082         }
    1083       }
    1084     }
    1085   }
    1086   return fail_cnt;
    1087 }
    1088
    1089 // Create a new table and using alternate hash code, populate the new table
    1090 // with the existing strings.   Set flag to use the alternate hash code afterwards.
    1091 void StringTable::rehash_table() {
    1092   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
    1093   // This should never happen with -Xshare:dump but it might in testing mode.
    1094   if (DumpSharedSpaces) return;
    1095   StringTable* new_table = new StringTable();
    1096
    1097   // Rehash the table
    1098   the_table()->move_to(new_table);
    1099
    1100   // Delete the table and buckets (entries are reused in new table).
    1101   delete _the_table;
    1102   // Don't check if we need rehashing until the table gets unbalanced again.
    1103   // Then rehash with a new global seed.
    1104   _needs_rehashing = false;
    1105   _the_table = new_table;
    1106 }