Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "classfile/altHashing.hpp"

 #include "classfile/javaClasses.hpp"

 #include "classfile/symbolTable.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "gc_interface/collectedHeap.inline.hpp"

 #include "memory/allocation.inline.hpp"

 #include "memory/filemap.hpp"

 #include "memory/gcLocker.inline.hpp"

 #include "oops/oop.inline.hpp"

 #include "oops/oop.inline2.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "utilities/hashtable.inline.hpp"

 #if INCLUDE_ALL_GCS

 #include "gc_implementation/g1/g1StringDedup.hpp"

 #endif

 // --------------------------------------------------------------------------

 // the number of buckets a thread claims

 const int ClaimChunkSize = 32;

 SymbolTable* SymbolTable::_the_table = NULL;

 // Static arena for symbols that are not deallocated

 Arena* SymbolTable::_arena = NULL;

 bool SymbolTable::_needs_rehashing = false;

 Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) {

   assert (len <= Symbol::max_length(), "should be checked by caller");

   Symbol* sym;

   if (DumpSharedSpaces) {

     // Allocate all symbols to CLD shared metaspace

     sym = new (len, ClassLoaderData::the_null_class_loader_data(), THREAD) Symbol(name, len, -1);

   } else if (c_heap) {

     // refcount starts as 1

     sym = new (len, THREAD) Symbol(name, len, 1);

     assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");

   } else {

     // Allocate to global arena

     sym = new (len, arena(), THREAD) Symbol(name, len, -1);

   }

   return sym;

 }

 void SymbolTable::initialize_symbols(int arena_alloc_size) {

   // Initialize the arena for global symbols, size passed in depends on CDS.

   if (arena_alloc_size == 0) {

     _arena = new (mtSymbol) Arena();

   } else {

     _arena = new (mtSymbol) Arena(arena_alloc_size);

   }

 }

 // Call function for all symbols in the symbol table.

 void SymbolTable::symbols_do(SymbolClosure *cl) {

   const int n = the_table()->table_size();

   for (int i = 0; i < n; i++) {

     for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);

          p != NULL;

          p = p->next()) {

       cl->do_symbol(p->literal_addr());

     }

   }

 }

 int SymbolTable::_symbols_removed = 0;

 int SymbolTable::_symbols_counted = 0;

 volatile int SymbolTable::_parallel_claimed_idx = 0;

 void SymbolTable::buckets_unlink(int start_idx, int end_idx, int* processed, int* removed, size_t* memory_total) {

   for (int i = start_idx; i < end_idx; ++i) {

     HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);

     HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);

     while (entry != NULL) {

       // Shared entries are normally at the end of the bucket and if we run into

       // a shared entry, then there is nothing more to remove. However, if we

       // have rehashed the table, then the shared entries are no longer at the

       // end of the bucket.

       if (entry->is_shared() && !use_alternate_hashcode()) {

         break;

       }

       Symbol* s = entry->literal();

       (*memory_total) += s->size();

       (*processed)++;

       assert(s != NULL, "just checking");

       // If reference count is zero, remove.

       if (s->refcount() == 0) {

         assert(!entry->is_shared(), "shared entries should be kept live");

         delete s;

         (*removed)++;

         *p = entry->next();

         the_table()->free_entry(entry);

       } else {

         p = entry->next_addr();

       }

       // get next entry

       entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);

     }

   }

 }

 // Remove unreferenced symbols from the symbol table

 // This is done late during GC.

 void SymbolTable::unlink(int* processed, int* removed) {

   size_t memory_total = 0;

   buckets_unlink(0, the_table()->table_size(), processed, removed, &memory_total);

   _symbols_removed += *removed;

   _symbols_counted += *processed;

   // Exclude printing for normal PrintGCDetails because people parse

   // this output.

   if (PrintGCDetails && Verbose && WizardMode) {

     gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", *processed,

                         (memory_total*HeapWordSize)/1024);

   }

 }

 void SymbolTable::possibly_parallel_unlink(int* processed, int* removed) {

   const int limit = the_table()->table_size();

   size_t memory_total = 0;

   for (;;) {

     // Grab next set of buckets to scan

     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;

     if (start_idx >= limit) {

       // End of table

       break;

     }

     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);

     buckets_unlink(start_idx, end_idx, processed, removed, &memory_total);

   }

   Atomic::add(*processed, &_symbols_counted);

   Atomic::add(*removed, &_symbols_removed);

   // Exclude printing for normal PrintGCDetails because people parse

   // this output.

   if (PrintGCDetails && Verbose && WizardMode) {

     gclog_or_tty->print(" [Symbols: scanned=%d removed=%d size=" SIZE_FORMAT "K] ", *processed, *removed,

                         (memory_total*HeapWordSize)/1024);

   }

 }

 // Create a new table and using alternate hash code, populate the new table

 // with the existing strings.   Set flag to use the alternate hash code afterwards.

 void SymbolTable::rehash_table() {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   // This should never happen with -Xshare:dump but it might in testing mode.

   if (DumpSharedSpaces) return;

   // Create a new symbol table

   SymbolTable* new_table = new SymbolTable();

   the_table()->move_to(new_table);

   // Delete the table and buckets (entries are reused in new table).

   delete _the_table;

   // Don't check if we need rehashing until the table gets unbalanced again.

   // Then rehash with a new global seed.

   _needs_rehashing = false;

   _the_table = new_table;

 }

 // Lookup a symbol in a bucket.

 Symbol* SymbolTable::lookup(int index, const char* name,

                               int len, unsigned int hash) {

   int count = 0;

   for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {

     count++;  // count all entries in this bucket, not just ones with same hash

     if (e->hash() == hash) {

       Symbol* sym = e->literal();

       if (sym->equals(name, len)) {

         // something is referencing this symbol now.

         sym->increment_refcount();

         return sym;

       }

     }

   }

   // If the bucket size is too deep check if this hash code is insufficient.

   if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {

     _needs_rehashing = check_rehash_table(count);

   }

   return NULL;

 }

 // Pick hashing algorithm.

 unsigned int SymbolTable::hash_symbol(const char* s, int len) {

   return use_alternate_hashcode() ?

            AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :

            java_lang_String::hash_code(s, len);

 }

 // We take care not to be blocking while holding the

 // SymbolTable_lock. Otherwise, the system might deadlock, since the

 // symboltable is used during compilation (VM_thread) The lock free

 // synchronization is simplified by the fact that we do not delete

 // entries in the symbol table during normal execution (only during

 // safepoints).

 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {

   unsigned int hashValue = hash_symbol(name, len);

   int index = the_table()->hash_to_index(hashValue);

   Symbol* s = the_table()->lookup(index, name, len, hashValue);

   // Found

   if (s != NULL) return s;

   // Grab SymbolTable_lock first.

   MutexLocker ml(SymbolTable_lock, THREAD);

   // Otherwise, add to symbol to table

   return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);

 }

 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {

   char* buffer;

   int index, len;

   unsigned int hashValue;

   char* name;

   {

     debug_only(No_Safepoint_Verifier nsv;)

     name = (char*)sym->base() + begin;

     len = end - begin;

     hashValue = hash_symbol(name, len);

     index = the_table()->hash_to_index(hashValue);

     Symbol* s = the_table()->lookup(index, name, len, hashValue);

     // Found

     if (s != NULL) return s;

   }

   // Otherwise, add to symbol to table. Copy to a C string first.

   char stack_buf[128];

   ResourceMark rm(THREAD);

   if (len <= 128) {

     buffer = stack_buf;

   } else {

     buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);

   }

   for (int i=0; i<len; i++) {

     buffer[i] = name[i];

   }

   // Make sure there is no safepoint in the code above since name can't move.

   // We can't include the code in No_Safepoint_Verifier because of the

   // ResourceMark.

   // Grab SymbolTable_lock first.

   MutexLocker ml(SymbolTable_lock, THREAD);

   return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);

 }

 Symbol* SymbolTable::lookup_only(const char* name, int len,

                                    unsigned int& hash) {

   hash = hash_symbol(name, len);

   int index = the_table()->hash_to_index(hash);

   Symbol* s = the_table()->lookup(index, name, len, hash);

   return s;

 }

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

 // Do not create any new symbols

 // Do not increment the reference count to keep this alive

 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){

   unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());

   int index = the_table()->hash_to_index(hash);

   for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {

     if (e->hash() == hash) {

       Symbol* literal_sym = e->literal();

       if (sym == literal_sym) {

         return e->literal_addr();

       }

     }

   }

   return NULL;

 }

 // Suggestion: Push unicode-based lookup all the way into the hashing

 // and probing logic, so there is no need for convert_to_utf8 until

 // an actual new Symbol* is created.

 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {

   int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);

   char stack_buf[128];

   if (utf8_length < (int) sizeof(stack_buf)) {

     char* chars = stack_buf;

     UNICODE::convert_to_utf8(name, utf16_length, chars);

     return lookup(chars, utf8_length, THREAD);

   } else {

     ResourceMark rm(THREAD);

     char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;

     UNICODE::convert_to_utf8(name, utf16_length, chars);

     return lookup(chars, utf8_length, THREAD);

   }

 }

 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,

                                            unsigned int& hash) {

   int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);

   char stack_buf[128];

   if (utf8_length < (int) sizeof(stack_buf)) {

     char* chars = stack_buf;

     UNICODE::convert_to_utf8(name, utf16_length, chars);

     return lookup_only(chars, utf8_length, hash);

   } else {

     ResourceMark rm;

     char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;

     UNICODE::convert_to_utf8(name, utf16_length, chars);

     return lookup_only(chars, utf8_length, hash);

   }

 }

 void SymbolTable::add(ClassLoaderData* loader_data, constantPoolHandle cp,

                       int names_count,

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

                       unsigned int* hashValues, TRAPS) {

   // Grab SymbolTable_lock first.

   MutexLocker ml(SymbolTable_lock, THREAD);

   SymbolTable* table = the_table();

   bool added = table->basic_add(loader_data, cp, names_count, names, lengths,

                                 cp_indices, hashValues, CHECK);

   if (!added) {

     // do it the hard way

     for (int i=0; i<names_count; i++) {

       int index = table->hash_to_index(hashValues[i]);

       bool c_heap = !loader_data->is_the_null_class_loader_data();

       Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);

       cp->symbol_at_put(cp_indices[i], sym);

     }

   }

 }

 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {

   unsigned int hash;

   Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);

   if (result != NULL) {

     return result;

   }

   // Grab SymbolTable_lock first.

   MutexLocker ml(SymbolTable_lock, THREAD);

   SymbolTable* table = the_table();

   int index = table->hash_to_index(hash);

   return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);

 }

 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,

                                unsigned int hashValue_arg, bool c_heap, TRAPS) {

   assert(!Universe::heap()->is_in_reserved(name),

          "proposed name of symbol must be stable");

   // Don't allow symbols to be created which cannot fit in a Symbol*.

   if (len > Symbol::max_length()) {

     THROW_MSG_0(vmSymbols::java_lang_InternalError(),

                 "name is too long to represent");

   }

   // Cannot hit a safepoint in this function because the "this" pointer can move.

   No_Safepoint_Verifier nsv;

   // Check if the symbol table has been rehashed, if so, need to recalculate

   // the hash value and index.

   unsigned int hashValue;

   int index;

   if (use_alternate_hashcode()) {

     hashValue = hash_symbol((const char*)name, len);

     index = hash_to_index(hashValue);

   } else {

     hashValue = hashValue_arg;

     index = index_arg;

   }

   // Since look-up was done lock-free, we need to check if another

   // thread beat us in the race to insert the symbol.

   Symbol* test = lookup(index, (char*)name, len, hashValue);

   if (test != NULL) {

     // A race occurred and another thread introduced the symbol.

     assert(test->refcount() != 0, "lookup should have incremented the count");

     return test;

   }

   // Create a new symbol.

   Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);

   assert(sym->equals((char*)name, len), "symbol must be properly initialized");

   HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);

   add_entry(index, entry);

   return sym;

 }

 // This version of basic_add adds symbols in batch from the constant pool

 // parsing.

 bool SymbolTable::basic_add(ClassLoaderData* loader_data, constantPoolHandle cp,

                             int names_count,

                             const char** names, int* lengths,

                             int* cp_indices, unsigned int* hashValues,

                             TRAPS) {

   // Check symbol names are not too long.  If any are too long, don't add any.

   for (int i = 0; i< names_count; i++) {

     if (lengths[i] > Symbol::max_length()) {

       THROW_MSG_0(vmSymbols::java_lang_InternalError(),

                   "name is too long to represent");

     }

   }

   // Cannot hit a safepoint in this function because the "this" pointer can move.

   No_Safepoint_Verifier nsv;

   for (int i=0; i<names_count; i++) {

     // Check if the symbol table has been rehashed, if so, need to recalculate

     // the hash value.

     unsigned int hashValue;

     if (use_alternate_hashcode()) {

       hashValue = hash_symbol(names[i], lengths[i]);

     } else {

       hashValue = hashValues[i];

     }

     // Since look-up was done lock-free, we need to check if another

     // thread beat us in the race to insert the symbol.

     int index = hash_to_index(hashValue);

     Symbol* test = lookup(index, names[i], lengths[i], hashValue);

     if (test != NULL) {

       // A race occurred and another thread introduced the symbol, this one

       // will be dropped and collected. Use test instead.

       cp->symbol_at_put(cp_indices[i], test);

       assert(test->refcount() != 0, "lookup should have incremented the count");

     } else {

       // Create a new symbol.  The null class loader is never unloaded so these

       // are allocated specially in a permanent arena.

       bool c_heap = !loader_data->is_the_null_class_loader_data();

       Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));

       assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized");  // why wouldn't it be???

       HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);

       add_entry(index, entry);

       cp->symbol_at_put(cp_indices[i], sym);

     }

   }

   return true;

 }

 void SymbolTable::verify() {

   for (int i = 0; i < the_table()->table_size(); ++i) {

     HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);

     for ( ; p != NULL; p = p->next()) {

       Symbol* s = (Symbol*)(p->literal());

       guarantee(s != NULL, "symbol is NULL");

       unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());

       guarantee(p->hash() == h, "broken hash in symbol table entry");

       guarantee(the_table()->hash_to_index(h) == i,

                 "wrong index in symbol table");

     }

   }

 }

 void SymbolTable::dump(outputStream* st) {

   the_table()->dump_table(st, "SymbolTable");

 }

 //---------------------------------------------------------------------------

 // Non-product code

 #ifndef PRODUCT

 void SymbolTable::print_histogram() {

   MutexLocker ml(SymbolTable_lock);

   const int results_length = 100;

   int results[results_length];

   int i,j;

   // initialize results to zero

   for (j = 0; j < results_length; j++) {

     results[j] = 0;

   }

   int total = 0;

   int max_symbols = 0;

   int out_of_range = 0;

   int memory_total = 0;

   int count = 0;

   for (i = 0; i < the_table()->table_size(); i++) {

     HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);

     for ( ; p != NULL; p = p->next()) {

       memory_total += p->literal()->size();

       count++;

       int counter = p->literal()->utf8_length();

       total += counter;

       if (counter < results_length) {

         results[counter]++;

       } else {

         out_of_range++;

       }

       max_symbols = MAX2(max_symbols, counter);

     }

   }

   tty->print_cr("Symbol Table:");

   tty->print_cr("Total number of symbols  %5d", count);

   tty->print_cr("Total size in memory     %5dK",

           (memory_total*HeapWordSize)/1024);

   tty->print_cr("Total counted            %5d", _symbols_counted);

   tty->print_cr("Total removed            %5d", _symbols_removed);

   if (_symbols_counted > 0) {

     tty->print_cr("Percent removed          %3.2f",

           ((float)_symbols_removed/(float)_symbols_counted)* 100);

   }

   tty->print_cr("Reference counts         %5d", Symbol::_total_count);

   tty->print_cr("Symbol arena size        %5d used %5d",

                  arena()->size_in_bytes(), arena()->used());

   tty->print_cr("Histogram of symbol length:");

   tty->print_cr("%8s %5d", "Total  ", total);

   tty->print_cr("%8s %5d", "Maximum", max_symbols);

   tty->print_cr("%8s %3.2f", "Average",

           ((float) total / (float) the_table()->table_size()));

   tty->print_cr("%s", "Histogram:");

   tty->print_cr(" %s %29s", "Length", "Number chains that length");

   for (i = 0; i < results_length; i++) {

     if (results[i] > 0) {

       tty->print_cr("%6d %10d", i, results[i]);

     }

   }

   if (Verbose) {

     int line_length = 70;

     tty->print_cr("%s %30s", " Length", "Number chains that length");

     for (i = 0; i < results_length; i++) {

       if (results[i] > 0) {

         tty->print("%4d", i);

         for (j = 0; (j < results[i]) && (j < line_length);  j++) {

           tty->print("%1s", "*");

         }

         if (j == line_length) {

           tty->print("%1s", "+");

         }

         tty->cr();

       }

     }

   }

   tty->print_cr(" %s %d: %d\n", "Number chains longer than",

                     results_length, out_of_range);

 }

 void SymbolTable::print() {

   for (int i = 0; i < the_table()->table_size(); ++i) {

     HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);

     HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);

     if (entry != NULL) {

       while (entry != NULL) {

         tty->print(PTR_FORMAT " ", entry->literal());

         entry->literal()->print();

         tty->print(" %d", entry->literal()->refcount());

         p = entry->next_addr();

         entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);

       }

       tty->cr();

     }

   }

 }

 #endif // PRODUCT

 // --------------------------------------------------------------------------

 #ifdef ASSERT

 class StableMemoryChecker : public StackObj {

   enum { _bufsize = wordSize*4 };

   address _region;

   jint    _size;

   u1      _save_buf[_bufsize];

   int sample(u1* save_buf) {

     if (_size <= _bufsize) {

       memcpy(save_buf, _region, _size);

       return _size;

     } else {

       // copy head and tail

       memcpy(&save_buf[0],          _region,                      _bufsize/2);

       memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);

       return (_bufsize/2)*2;

     }

   }

  public:

   StableMemoryChecker(const void* region, jint size) {

     _region = (address) region;

     _size   = size;

     sample(_save_buf);

   }

   bool verify() {

     u1 check_buf[sizeof(_save_buf)];

     int check_size = sample(check_buf);

     return (0 == memcmp(_save_buf, check_buf, check_size));

   }

   void set_region(const void* region) { _region = (address) region; }

 };

 #endif

 // --------------------------------------------------------------------------

 StringTable* StringTable::_the_table = NULL;

 bool StringTable::_needs_rehashing = false;

 volatile int StringTable::_parallel_claimed_idx = 0;

 // Pick hashing algorithm

 unsigned int StringTable::hash_string(const jchar* s, int len) {

   return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :

                                     java_lang_String::hash_code(s, len);

 }

 oop StringTable::lookup(int index, jchar* name,

                         int len, unsigned int hash) {

   int count = 0;

   for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {

     count++;

     if (l->hash() == hash) {

       if (java_lang_String::equals(l->literal(), name, len)) {

         return l->literal();

       }

     }

   }

   // If the bucket size is too deep check if this hash code is insufficient.

   if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {

     _needs_rehashing = check_rehash_table(count);

   }

   return NULL;

 }

 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,

                            int len, unsigned int hashValue_arg, TRAPS) {

   assert(java_lang_String::equals(string(), name, len),

          "string must be properly initialized");

   // Cannot hit a safepoint in this function because the "this" pointer can move.

   No_Safepoint_Verifier nsv;

   // Check if the symbol table has been rehashed, if so, need to recalculate

   // the hash value and index before second lookup.

   unsigned int hashValue;

   int index;

   if (use_alternate_hashcode()) {

     hashValue = hash_string(name, len);

     index = hash_to_index(hashValue);

   } else {

     hashValue = hashValue_arg;

     index = index_arg;

   }

   // Since look-up was done lock-free, we need to check if another

   // thread beat us in the race to insert the symbol.

   oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)

   if (test != NULL) {

     // Entry already added

     return test;

   }

   HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());

   add_entry(index, entry);

   return string();

 }

 oop StringTable::lookup(Symbol* symbol) {

   ResourceMark rm;

   int length;

   jchar* chars = symbol->as_unicode(length);

   return lookup(chars, length);

 }

 oop StringTable::lookup(jchar* name, int len) {

   unsigned int hash = hash_string(name, len);

   int index = the_table()->hash_to_index(hash);

   return the_table()->lookup(index, name, len, hash);

 }

 oop StringTable::intern(Handle string_or_null, jchar* name,

                         int len, TRAPS) {

   unsigned int hashValue = hash_string(name, len);

   int index = the_table()->hash_to_index(hashValue);

   oop found_string = the_table()->lookup(index, name, len, hashValue);

   // Found

   if (found_string != NULL) return found_string;

   debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));

   assert(!Universe::heap()->is_in_reserved(name),

          "proposed name of symbol must be stable");

   Handle string;

   // try to reuse the string if possible

   if (!string_or_null.is_null()) {

     string = string_or_null;

   } else {

     string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);

   }

 #if INCLUDE_ALL_GCS

   if (G1StringDedup::is_enabled()) {

     // Deduplicate the string before it is interned. Note that we should never

     // deduplicate a string after it has been interned. Doing so will counteract

     // compiler optimizations done on e.g. interned string literals.

     G1StringDedup::deduplicate(string());

   }

 #endif

   // Grab the StringTable_lock before getting the_table() because it could

   // change at safepoint.

   MutexLocker ml(StringTable_lock, THREAD);

   // Otherwise, add to symbol to table

   return the_table()->basic_add(index, string, name, len,

                                 hashValue, CHECK_NULL);

 }

 oop StringTable::intern(Symbol* symbol, TRAPS) {

   if (symbol == NULL) return NULL;

   ResourceMark rm(THREAD);

   int length;

   jchar* chars = symbol->as_unicode(length);

   Handle string;

   oop result = intern(string, chars, length, CHECK_NULL);

   return result;

 }

 oop StringTable::intern(oop string, TRAPS)

 {

   if (string == NULL) return NULL;

   ResourceMark rm(THREAD);

   int length;

   Handle h_string (THREAD, string);

   jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);

   oop result = intern(h_string, chars, length, CHECK_NULL);

   return result;

 }

 oop StringTable::intern(const char* utf8_string, TRAPS) {

   if (utf8_string == NULL) return NULL;

   ResourceMark rm(THREAD);

   int length = UTF8::unicode_length(utf8_string);

   jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);

   UTF8::convert_to_unicode(utf8_string, chars, length);

   Handle string;

   oop result = intern(string, chars, length, CHECK_NULL);

   return result;

 }

 void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {

   buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), processed, removed);

 }

 void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {

   // Readers of the table are unlocked, so we should only be removing

   // entries at a safepoint.

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   const int limit = the_table()->table_size();

   for (;;) {

     // Grab next set of buckets to scan

     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;

     if (start_idx >= limit) {

       // End of table

       break;

     }

     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);

     buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, processed, removed);

   }

 }

 void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {

   const int limit = the_table()->table_size();

   assert(0 <= start_idx && start_idx <= limit,

          err_msg("start_idx (" INT32_FORMAT ") is out of bounds", start_idx));

   assert(0 <= end_idx && end_idx <= limit,

          err_msg("end_idx (" INT32_FORMAT ") is out of bounds", end_idx));

   assert(start_idx <= end_idx,

          err_msg("Index ordering: start_idx=" INT32_FORMAT", end_idx=" INT32_FORMAT,

                  start_idx, end_idx));

   for (int i = start_idx; i < end_idx; i += 1) {

     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);

     while (entry != NULL) {

       assert(!entry->is_shared(), "CDS not used for the StringTable");

       f->do_oop((oop*)entry->literal_addr());

       entry = entry->next();

     }

   }

 }

 void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, int* processed, int* removed) {

   const int limit = the_table()->table_size();

   assert(0 <= start_idx && start_idx <= limit,

          err_msg("start_idx (" INT32_FORMAT ") is out of bounds", start_idx));

   assert(0 <= end_idx && end_idx <= limit,

          err_msg("end_idx (" INT32_FORMAT ") is out of bounds", end_idx));

   assert(start_idx <= end_idx,

          err_msg("Index ordering: start_idx=" INT32_FORMAT", end_idx=" INT32_FORMAT,

                  start_idx, end_idx));

   for (int i = start_idx; i < end_idx; ++i) {

     HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);

     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);

     while (entry != NULL) {

       assert(!entry->is_shared(), "CDS not used for the StringTable");

       if (is_alive->do_object_b(entry->literal())) {

         if (f != NULL) {

           f->do_oop((oop*)entry->literal_addr());

         }

         p = entry->next_addr();

       } else {

         *p = entry->next();

         the_table()->free_entry(entry);

         (*removed)++;

       }

       (*processed)++;

       entry = *p;

     }

   }

 }

 void StringTable::oops_do(OopClosure* f) {

   buckets_oops_do(f, 0, the_table()->table_size());

 }

 void StringTable::possibly_parallel_oops_do(OopClosure* f) {

   const int limit = the_table()->table_size();

   for (;;) {

     // Grab next set of buckets to scan

     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;

     if (start_idx >= limit) {

       // End of table

       break;

     }

     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);

     buckets_oops_do(f, start_idx, end_idx);

   }

 }

 // This verification is part of Universe::verify() and needs to be quick.

 // See StringTable::verify_and_compare() below for exhaustive verification.

 void StringTable::verify() {

   for (int i = 0; i < the_table()->table_size(); ++i) {

     HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);

     for ( ; p != NULL; p = p->next()) {

       oop s = p->literal();

       guarantee(s != NULL, "interned string is NULL");

       unsigned int h = java_lang_String::hash_string(s);

       guarantee(p->hash() == h, "broken hash in string table entry");

       guarantee(the_table()->hash_to_index(h) == i,

                 "wrong index in string table");

     }

   }

 }

 void StringTable::dump(outputStream* st) {

   the_table()->dump_table(st, "StringTable");

 }

 StringTable::VerifyRetTypes StringTable::compare_entries(

                                       int bkt1, int e_cnt1,

                                       HashtableEntry<oop, mtSymbol>* e_ptr1,

                                       int bkt2, int e_cnt2,

                                       HashtableEntry<oop, mtSymbol>* e_ptr2) {

   // These entries are sanity checked by verify_and_compare_entries()

   // before this function is called.

   oop str1 = e_ptr1->literal();

   oop str2 = e_ptr2->literal();

   if (str1 == str2) {

     tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "

                   "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",

                   (void *)str1, bkt1, e_cnt1, bkt2, e_cnt2);

     return _verify_fail_continue;

   }

   if (java_lang_String::equals(str1, str2)) {

     tty->print_cr("ERROR: identical String values in entry @ "

                   "bucket[%d][%d] and entry @ bucket[%d][%d]",

                   bkt1, e_cnt1, bkt2, e_cnt2);

     return _verify_fail_continue;

   }

   return _verify_pass;

 }

 StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,

                                       HashtableEntry<oop, mtSymbol>* e_ptr,

                                       StringTable::VerifyMesgModes mesg_mode) {

   VerifyRetTypes ret = _verify_pass;  // be optimistic

   oop str = e_ptr->literal();

   if (str == NULL) {

     if (mesg_mode == _verify_with_mesgs) {

       tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,

                     e_cnt);

     }

     // NULL oop means no more verifications are possible

     return _verify_fail_done;

   }

   if (str->klass() != SystemDictionary::String_klass()) {

     if (mesg_mode == _verify_with_mesgs) {

       tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",

                     bkt, e_cnt);

     }

     // not a String means no more verifications are possible

     return _verify_fail_done;

   }

   unsigned int h = java_lang_String::hash_string(str);

   if (e_ptr->hash() != h) {

     if (mesg_mode == _verify_with_mesgs) {

       tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "

                     "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);

     }

     ret = _verify_fail_continue;

   }

   if (the_table()->hash_to_index(h) != bkt) {

     if (mesg_mode == _verify_with_mesgs) {

       tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "

                     "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,

                     the_table()->hash_to_index(h));

     }

     ret = _verify_fail_continue;

   }

   return ret;

 }

 // See StringTable::verify() above for the quick verification that is

 // part of Universe::verify(). This verification is exhaustive and

 // reports on every issue that is found. StringTable::verify() only

 // reports on the first issue that is found.

 //

 // StringTable::verify_entry() checks:

 // - oop value != NULL (same as verify())

 // - oop value is a String

 // - hash(String) == hash in entry (same as verify())

 // - index for hash == index of entry (same as verify())

 //

 // StringTable::compare_entries() checks:

 // - oops are unique across all entries

 // - String values are unique across all entries

 //

 int StringTable::verify_and_compare_entries() {

   assert(StringTable_lock->is_locked(), "sanity check");

   int  fail_cnt = 0;

   // first, verify all the entries individually:

   for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {

     HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);

     for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {

       VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);

       if (ret != _verify_pass) {

         fail_cnt++;

       }

     }

   }

   // Optimization: if the above check did not find any failures, then

   // the comparison loop below does not need to call verify_entry()

   // before calling compare_entries(). If there were failures, then we

   // have to call verify_entry() to see if the entry can be passed to

   // compare_entries() safely. When we call verify_entry() in the loop

   // below, we do so quietly to void duplicate messages and we don't

   // increment fail_cnt because the failures have already been counted.

   bool need_entry_verify = (fail_cnt != 0);

   // second, verify all entries relative to each other:

   for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {

     HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);

     for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {

       if (need_entry_verify) {

         VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,

                                           _verify_quietly);

         if (ret == _verify_fail_done) {

           // cannot use the current entry to compare against other entries

           continue;

         }

       }

       for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {

         HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);

         int e_cnt2;

         for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {

           if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {

             // skip the entries up to and including the one that

             // we're comparing against

             continue;

           }

           if (need_entry_verify) {

             VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,

                                               _verify_quietly);

             if (ret == _verify_fail_done) {

               // cannot compare against this entry

               continue;

             }

           }

           // compare two entries, report and count any failures:

           if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)

               != _verify_pass) {

             fail_cnt++;

           }

         }

       }

     }

   }

   return fail_cnt;

 }

 // Create a new table and using alternate hash code, populate the new table

 // with the existing strings.   Set flag to use the alternate hash code afterwards.

 void StringTable::rehash_table() {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   // This should never happen with -Xshare:dump but it might in testing mode.

   if (DumpSharedSpaces) return;

   StringTable* new_table = new StringTable();

   // Rehash the table

   the_table()->move_to(new_table);

   // Delete the table and buckets (entries are reused in new table).

   delete _the_table;

   // Don't check if we need rehashing until the table gets unbalanced again.

   // Then rehash with a new global seed.

   _needs_rehashing = false;

   _the_table = new_table;

 }