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 #include "precompiled.hpp"
  26 #include "classfile/altHashing.hpp"
  27 #include "classfile/compactHashtable.inline.hpp"
  28 #include "classfile/javaClasses.inline.hpp"
  29 #include "classfile/stringTable.hpp"
  30 #include "classfile/systemDictionary.hpp"
  31 #include "gc/shared/collectedHeap.inline.hpp"
  32 #include "gc/shared/gcLocker.inline.hpp"
  33 #include "logging/log.hpp"
  34 #include "memory/allocation.inline.hpp"
  35 #include "memory/filemap.hpp"
  36 #include "memory/metaspaceShared.hpp"
  37 #include "memory/resourceArea.hpp"
  38 #include "oops/access.inline.hpp"
  39 #include "oops/oop.inline.hpp"
  40 #include "runtime/atomic.hpp"
  41 #include "runtime/mutexLocker.hpp"
  42 #include "services/diagnosticCommand.hpp"
  43 #include "utilities/hashtable.inline.hpp"
  44 #include "utilities/macros.hpp"
  45 #if INCLUDE_ALL_GCS
  46 #include "gc/g1/g1CollectedHeap.hpp"
  47 #include "gc/g1/g1StringDedup.hpp"
  48 #endif
  49 
  50 // the number of buckets a thread claims
  51 const int ClaimChunkSize = 32;
  52 
  53 #ifdef ASSERT
  54 class StableMemoryChecker : public StackObj {
  55   enum { _bufsize = wordSize*4 };
  56 
  57   address _region;
  58   jint    _size;
  59   u1      _save_buf[_bufsize];
  60 
  61   int sample(u1* save_buf) {
  62     if (_size <= _bufsize) {
  63       memcpy(save_buf, _region, _size);
  64       return _size;
  65     } else {
  66       // copy head and tail
  67       memcpy(&save_buf[0],          _region,                      _bufsize/2);
  68       memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
  69       return (_bufsize/2)*2;
  70     }
  71   }
  72 
  73  public:
  74   StableMemoryChecker(const void* region, jint size) {
  75     _region = (address) region;
  76     _size   = size;
  77     sample(_save_buf);
  78   }
  79 
  80   bool verify() {
  81     u1 check_buf[sizeof(_save_buf)];
  82     int check_size = sample(check_buf);
  83     return (0 == memcmp(_save_buf, check_buf, check_size));
  84   }
  85 
  86   void set_region(const void* region) { _region = (address) region; }
  87 };
  88 #endif
  89 
  90 
  91 // --------------------------------------------------------------------------
  92 StringTable* StringTable::_the_table = NULL;
  93 bool StringTable::_shared_string_mapped = false;
  94 bool StringTable::_needs_rehashing = false;
  95 
  96 volatile int StringTable::_parallel_claimed_idx = 0;
  97 
  98 CompactHashtable<oop, char> StringTable::_shared_table;
  99 
 100 // Pick hashing algorithm
 101 unsigned int StringTable::hash_string(const jchar* s, int len) {
 102   return use_alternate_hashcode() ? alt_hash_string(s, len) :
 103                                     java_lang_String::hash_code(s, len);
 104 }
 105 
 106 unsigned int StringTable::alt_hash_string(const jchar* s, int len) {
 107   return AltHashing::murmur3_32(seed(), s, len);
 108 }
 109 
 110 unsigned int StringTable::hash_string(oop string) {
 111   EXCEPTION_MARK;
 112   if (string == NULL) {
 113     return hash_string((jchar*)NULL, 0);
 114   }
 115   ResourceMark rm(THREAD);
 116   // All String oops are hashed as unicode
 117   int length;
 118   jchar* chars = java_lang_String::as_unicode_string(string, length, THREAD);
 119   if (chars != NULL) {
 120     return hash_string(chars, length);
 121   } else {
 122     vm_exit_out_of_memory(length, OOM_MALLOC_ERROR, "unable to create Unicode string for verification");
 123     return 0;
 124   }
 125 }
 126 
 127 oop StringTable::string_object(HashtableEntry<oop, mtSymbol>* entry) {
 128   return RootAccess<ON_PHANTOM_OOP_REF>::oop_load(entry->literal_addr());
 129 }
 130 
 131 oop StringTable::string_object_no_keepalive(HashtableEntry<oop, mtSymbol>* entry) {
 132   // The AS_NO_KEEPALIVE peeks at the oop without keeping it alive.
 133   // This is *very dangerous* in general but is okay in this specific
 134   // case. The subsequent oop_load keeps the oop alive if it it matched
 135   // the jchar* string.
 136   return RootAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(entry->literal_addr());
 137 }
 138 
 139 void StringTable::set_string_object(HashtableEntry<oop, mtSymbol>* entry, oop string) {
 140   RootAccess<ON_PHANTOM_OOP_REF>::oop_store(entry->literal_addr(), string);
 141 }
 142 
 143 oop StringTable::lookup_shared(jchar* name, int len, unsigned int hash) {
 144   assert(hash == java_lang_String::hash_code(name, len),
 145          "hash must be computed using java_lang_String::hash_code");
 146   return _shared_table.lookup((const char*)name, hash, len);
 147 }
 148 
 149 oop StringTable::lookup_in_main_table(int index, jchar* name,
 150                                       int len, unsigned int hash) {
 151   int count = 0;
 152   for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
 153     count++;
 154     if (l->hash() == hash) {
 155       if (java_lang_String::equals(string_object_no_keepalive(l), name, len)) {
 156         // We must perform a new load with string_object() that keeps the string
 157         // alive as we must expose the oop as strongly reachable when exiting
 158         // this context, in case the oop gets published.
 159         return string_object(l);
 160       }
 161     }
 162   }
 163   // If the bucket size is too deep check if this hash code is insufficient.
 164   if (count >= rehash_count && !needs_rehashing()) {
 165     _needs_rehashing = check_rehash_table(count);
 166   }
 167   return NULL;
 168 }
 169 
 170 
 171 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
 172                            int len, unsigned int hashValue_arg, TRAPS) {
 173 
 174   assert(java_lang_String::equals(string(), name, len),
 175          "string must be properly initialized");
 176   // Cannot hit a safepoint in this function because the "this" pointer can move.
 177   NoSafepointVerifier nsv;
 178 
 179   // Check if the symbol table has been rehashed, if so, need to recalculate
 180   // the hash value and index before second lookup.
 181   unsigned int hashValue;
 182   int index;
 183   if (use_alternate_hashcode()) {
 184     hashValue = alt_hash_string(name, len);
 185     index = hash_to_index(hashValue);
 186   } else {
 187     hashValue = hashValue_arg;
 188     index = index_arg;
 189   }
 190 
 191   // Since look-up was done lock-free, we need to check if another
 192   // thread beat us in the race to insert the symbol.
 193 
 194   // No need to lookup the shared table from here since the caller (intern()) already did
 195   oop test = lookup_in_main_table(index, name, len, hashValue); // calls lookup(u1*, int)
 196   if (test != NULL) {
 197     // Entry already added
 198     return test;
 199   }
 200 
 201   HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
 202   add_entry(index, entry);
 203   return string();
 204 }
 205 
 206 
 207 oop StringTable::lookup(Symbol* symbol) {
 208   ResourceMark rm;
 209   int length;
 210   jchar* chars = symbol->as_unicode(length);
 211   return lookup(chars, length);
 212 }
 213 
 214 oop StringTable::lookup(jchar* name, int len) {
 215   // shared table always uses java_lang_String::hash_code
 216   unsigned int hash = java_lang_String::hash_code(name, len);
 217   oop string = lookup_shared(name, len, hash);
 218   if (string != NULL) {
 219     return string;
 220   }
 221   if (use_alternate_hashcode()) {
 222     hash = alt_hash_string(name, len);
 223   }
 224   int index = the_table()->hash_to_index(hash);
 225   string = the_table()->lookup_in_main_table(index, name, len, hash);
 226 
 227   return string;
 228 }
 229 
 230 oop StringTable::intern(Handle string_or_null, jchar* name,
 231                         int len, TRAPS) {
 232   // shared table always uses java_lang_String::hash_code
 233   unsigned int hashValue = java_lang_String::hash_code(name, len);
 234   oop found_string = lookup_shared(name, len, hashValue);
 235   if (found_string != NULL) {
 236     return found_string;
 237   }
 238   if (use_alternate_hashcode()) {
 239     hashValue = alt_hash_string(name, len);
 240   }
 241   int index = the_table()->hash_to_index(hashValue);
 242   found_string = the_table()->lookup_in_main_table(index, name, len, hashValue);
 243 
 244   // Found
 245   if (found_string != NULL) {
 246     return found_string;
 247   }
 248 
 249   debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
 250   assert(!Universe::heap()->is_in_reserved(name),
 251          "proposed name of symbol must be stable");
 252 
 253   HandleMark hm(THREAD);  // cleanup strings created
 254   Handle string;
 255   // try to reuse the string if possible
 256   if (!string_or_null.is_null()) {
 257     string = string_or_null;
 258   } else {
 259     string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
 260   }
 261 
 262 #if INCLUDE_ALL_GCS
 263   if (G1StringDedup::is_enabled()) {
 264     // Deduplicate the string before it is interned. Note that we should never
 265     // deduplicate a string after it has been interned. Doing so will counteract
 266     // compiler optimizations done on e.g. interned string literals.
 267     G1StringDedup::deduplicate(string());
 268   }
 269 #endif
 270 
 271   // Grab the StringTable_lock before getting the_table() because it could
 272   // change at safepoint.
 273   oop added_or_found;
 274   {
 275     MutexLocker ml(StringTable_lock, THREAD);
 276     // Otherwise, add to symbol to table
 277     added_or_found = the_table()->basic_add(index, string, name, len,
 278                                   hashValue, CHECK_NULL);
 279   }
 280 
 281   return added_or_found;
 282 }
 283 
 284 oop StringTable::intern(Symbol* symbol, TRAPS) {
 285   if (symbol == NULL) return NULL;
 286   ResourceMark rm(THREAD);
 287   int length;
 288   jchar* chars = symbol->as_unicode(length);
 289   Handle string;
 290   oop result = intern(string, chars, length, CHECK_NULL);
 291   return result;
 292 }
 293 
 294 
 295 oop StringTable::intern(oop string, TRAPS)
 296 {
 297   if (string == NULL) return NULL;
 298   ResourceMark rm(THREAD);
 299   int length;
 300   Handle h_string (THREAD, string);
 301   jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
 302   oop result = intern(h_string, chars, length, CHECK_NULL);
 303   return result;
 304 }
 305 
 306 
 307 oop StringTable::intern(const char* utf8_string, TRAPS) {
 308   if (utf8_string == NULL) return NULL;
 309   ResourceMark rm(THREAD);
 310   int length = UTF8::unicode_length(utf8_string);
 311   jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
 312   UTF8::convert_to_unicode(utf8_string, chars, length);
 313   Handle string;
 314   oop result = intern(string, chars, length, CHECK_NULL);
 315   return result;
 316 }
 317 
 318 void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
 319   BucketUnlinkContext context;
 320   buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), &context);
 321   _the_table->bulk_free_entries(&context);
 322   *processed = context._num_processed;
 323   *removed = context._num_removed;
 324 }
 325 
 326 void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
 327   // Readers of the table are unlocked, so we should only be removing
 328   // entries at a safepoint.
 329   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 330   const int limit = the_table()->table_size();
 331 
 332   BucketUnlinkContext context;
 333   for (;;) {
 334     // Grab next set of buckets to scan
 335     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
 336     if (start_idx >= limit) {
 337       // End of table
 338       break;
 339     }
 340 
 341     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
 342     buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, &context);
 343   }
 344   _the_table->bulk_free_entries(&context);
 345   *processed = context._num_processed;
 346   *removed = context._num_removed;
 347 }
 348 
 349 void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {
 350   const int limit = the_table()->table_size();
 351 
 352   assert(0 <= start_idx && start_idx <= limit,
 353          "start_idx (%d) is out of bounds", start_idx);
 354   assert(0 <= end_idx && end_idx <= limit,
 355          "end_idx (%d) is out of bounds", end_idx);
 356   assert(start_idx <= end_idx,
 357          "Index ordering: start_idx=%d, end_idx=%d",
 358          start_idx, end_idx);
 359 
 360   for (int i = start_idx; i < end_idx; i += 1) {
 361     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
 362     while (entry != NULL) {
 363       assert(!entry->is_shared(), "CDS not used for the StringTable");
 364 
 365       f->do_oop((oop*)entry->literal_addr());
 366 
 367       entry = entry->next();
 368     }
 369   }
 370 }
 371 
 372 void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context) {
 373   const int limit = the_table()->table_size();
 374 
 375   assert(0 <= start_idx && start_idx <= limit,
 376          "start_idx (%d) is out of bounds", start_idx);
 377   assert(0 <= end_idx && end_idx <= limit,
 378          "end_idx (%d) is out of bounds", end_idx);
 379   assert(start_idx <= end_idx,
 380          "Index ordering: start_idx=%d, end_idx=%d",
 381          start_idx, end_idx);
 382 
 383   for (int i = start_idx; i < end_idx; ++i) {
 384     HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
 385     HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
 386     while (entry != NULL) {
 387       assert(!entry->is_shared(), "CDS not used for the StringTable");
 388 
 389       if (is_alive->do_object_b(string_object_no_keepalive(entry))) {
 390         if (f != NULL) {
 391           f->do_oop(entry->literal_addr());
 392         }
 393         p = entry->next_addr();
 394       } else {
 395         *p = entry->next();
 396         context->free_entry(entry);
 397       }
 398       context->_num_processed++;
 399       entry = *p;
 400     }
 401   }
 402 }
 403 
 404 void StringTable::oops_do(OopClosure* f) {
 405   buckets_oops_do(f, 0, the_table()->table_size());
 406 }
 407 
 408 void StringTable::possibly_parallel_oops_do(OopClosure* f) {
 409   const int limit = the_table()->table_size();
 410 
 411   for (;;) {
 412     // Grab next set of buckets to scan
 413     int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
 414     if (start_idx >= limit) {
 415       // End of table
 416       break;
 417     }
 418 
 419     int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
 420     buckets_oops_do(f, start_idx, end_idx);
 421   }
 422 }
 423 
 424 // This verification is part of Universe::verify() and needs to be quick.
 425 // See StringTable::verify_and_compare() below for exhaustive verification.
 426 void StringTable::verify() {
 427   for (int i = 0; i < the_table()->table_size(); ++i) {
 428     HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
 429     for ( ; p != NULL; p = p->next()) {
 430       oop s = string_object_no_keepalive(p);
 431       guarantee(s != NULL, "interned string is NULL");
 432       unsigned int h = hash_string(s);
 433       guarantee(p->hash() == h, "broken hash in string table entry");
 434       guarantee(the_table()->hash_to_index(h) == i,
 435                 "wrong index in string table");
 436     }
 437   }
 438 }
 439 
 440 void StringTable::dump(outputStream* st, bool verbose) {
 441   if (!verbose) {
 442     the_table()->print_table_statistics(st, "StringTable");
 443   } else {
 444     Thread* THREAD = Thread::current();
 445     st->print_cr("VERSION: 1.1");
 446     for (int i = 0; i < the_table()->table_size(); ++i) {
 447       HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
 448       for ( ; p != NULL; p = p->next()) {
 449         oop s = string_object_no_keepalive(p);
 450         typeArrayOop value     = java_lang_String::value_no_keepalive(s);
 451         int          length    = java_lang_String::length(s);
 452         bool         is_latin1 = java_lang_String::is_latin1(s);
 453 
 454         if (length <= 0) {
 455           st->print("%d: ", length);
 456         } else {
 457           ResourceMark rm(THREAD);
 458           int utf8_length = length;
 459           char* utf8_string;
 460 
 461           if (!is_latin1) {
 462             jchar* chars = value->char_at_addr(0);
 463             utf8_string = UNICODE::as_utf8(chars, utf8_length);
 464           } else {
 465             jbyte* bytes = value->byte_at_addr(0);
 466             utf8_string = UNICODE::as_utf8(bytes, utf8_length);
 467           }
 468 
 469           st->print("%d: ", utf8_length);
 470           HashtableTextDump::put_utf8(st, utf8_string, utf8_length);
 471         }
 472         st->cr();
 473       }
 474     }
 475   }
 476 }
 477 
 478 StringTable::VerifyRetTypes StringTable::compare_entries(
 479                                       int bkt1, int e_cnt1,
 480                                       HashtableEntry<oop, mtSymbol>* e_ptr1,
 481                                       int bkt2, int e_cnt2,
 482                                       HashtableEntry<oop, mtSymbol>* e_ptr2) {
 483   // These entries are sanity checked by verify_and_compare_entries()
 484   // before this function is called.
 485   oop str1 = string_object_no_keepalive(e_ptr1);
 486   oop str2 = string_object_no_keepalive(e_ptr2);
 487 
 488   if (str1 == str2) {
 489     tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "
 490                   "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",
 491                   p2i(str1), bkt1, e_cnt1, bkt2, e_cnt2);
 492     return _verify_fail_continue;
 493   }
 494 
 495   if (java_lang_String::equals(str1, str2)) {
 496     tty->print_cr("ERROR: identical String values in entry @ "
 497                   "bucket[%d][%d] and entry @ bucket[%d][%d]",
 498                   bkt1, e_cnt1, bkt2, e_cnt2);
 499     return _verify_fail_continue;
 500   }
 501 
 502   return _verify_pass;
 503 }
 504 
 505 StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,
 506                                                       HashtableEntry<oop, mtSymbol>* e_ptr,
 507                                                       StringTable::VerifyMesgModes mesg_mode) {
 508 
 509   VerifyRetTypes ret = _verify_pass;  // be optimistic
 510 
 511   oop str = string_object_no_keepalive(e_ptr);
 512   if (str == NULL) {
 513     if (mesg_mode == _verify_with_mesgs) {
 514       tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,
 515                     e_cnt);
 516     }
 517     // NULL oop means no more verifications are possible
 518     return _verify_fail_done;
 519   }
 520 
 521   if (str->klass() != SystemDictionary::String_klass()) {
 522     if (mesg_mode == _verify_with_mesgs) {
 523       tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",
 524                     bkt, e_cnt);
 525     }
 526     // not a String means no more verifications are possible
 527     return _verify_fail_done;
 528   }
 529 
 530   unsigned int h = hash_string(str);
 531   if (e_ptr->hash() != h) {
 532     if (mesg_mode == _verify_with_mesgs) {
 533       tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "
 534                     "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);
 535     }
 536     ret = _verify_fail_continue;
 537   }
 538 
 539   if (the_table()->hash_to_index(h) != bkt) {
 540     if (mesg_mode == _verify_with_mesgs) {
 541       tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "
 542                     "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,
 543                     the_table()->hash_to_index(h));
 544     }
 545     ret = _verify_fail_continue;
 546   }
 547 
 548   return ret;
 549 }
 550 
 551 // See StringTable::verify() above for the quick verification that is
 552 // part of Universe::verify(). This verification is exhaustive and
 553 // reports on every issue that is found. StringTable::verify() only
 554 // reports on the first issue that is found.
 555 //
 556 // StringTable::verify_entry() checks:
 557 // - oop value != NULL (same as verify())
 558 // - oop value is a String
 559 // - hash(String) == hash in entry (same as verify())
 560 // - index for hash == index of entry (same as verify())
 561 //
 562 // StringTable::compare_entries() checks:
 563 // - oops are unique across all entries
 564 // - String values are unique across all entries
 565 //
 566 int StringTable::verify_and_compare_entries() {
 567   assert(StringTable_lock->is_locked(), "sanity check");
 568 
 569   int  fail_cnt = 0;
 570 
 571   // first, verify all the entries individually:
 572   for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {
 573     HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);
 574     for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {
 575       VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);
 576       if (ret != _verify_pass) {
 577         fail_cnt++;
 578       }
 579     }
 580   }
 581 
 582   // Optimization: if the above check did not find any failures, then
 583   // the comparison loop below does not need to call verify_entry()
 584   // before calling compare_entries(). If there were failures, then we
 585   // have to call verify_entry() to see if the entry can be passed to
 586   // compare_entries() safely. When we call verify_entry() in the loop
 587   // below, we do so quietly to void duplicate messages and we don't
 588   // increment fail_cnt because the failures have already been counted.
 589   bool need_entry_verify = (fail_cnt != 0);
 590 
 591   // second, verify all entries relative to each other:
 592   for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {
 593     HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);
 594     for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {
 595       if (need_entry_verify) {
 596         VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,
 597                                           _verify_quietly);
 598         if (ret == _verify_fail_done) {
 599           // cannot use the current entry to compare against other entries
 600           continue;
 601         }
 602       }
 603 
 604       for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {
 605         HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);
 606         int e_cnt2;
 607         for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {
 608           if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {
 609             // skip the entries up to and including the one that
 610             // we're comparing against
 611             continue;
 612           }
 613 
 614           if (need_entry_verify) {
 615             VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,
 616                                               _verify_quietly);
 617             if (ret == _verify_fail_done) {
 618               // cannot compare against this entry
 619               continue;
 620             }
 621           }
 622 
 623           // compare two entries, report and count any failures:
 624           if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)
 625               != _verify_pass) {
 626             fail_cnt++;
 627           }
 628         }
 629       }
 630     }
 631   }
 632   return fail_cnt;
 633 }
 634 
 635 // Create a new table and using alternate hash code, populate the new table
 636 // with the existing strings.   Set flag to use the alternate hash code afterwards.
 637 void StringTable::rehash_table() {
 638   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 639   // This should never happen with -Xshare:dump but it might in testing mode.
 640   if (DumpSharedSpaces) return;
 641   StringTable* new_table = new StringTable();
 642 
 643   // Rehash the table
 644   the_table()->move_to(new_table);
 645 
 646   // Delete the table and buckets (entries are reused in new table).
 647   delete _the_table;
 648   // Don't check if we need rehashing until the table gets unbalanced again.
 649   // Then rehash with a new global seed.
 650   _needs_rehashing = false;
 651   _the_table = new_table;
 652 }
 653 
 654 // Utility for dumping strings
 655 StringtableDCmd::StringtableDCmd(outputStream* output, bool heap) :
 656                                  DCmdWithParser(output, heap),
 657   _verbose("-verbose", "Dump the content of each string in the table",
 658            "BOOLEAN", false, "false") {
 659   _dcmdparser.add_dcmd_option(&_verbose);
 660 }
 661 
 662 void StringtableDCmd::execute(DCmdSource source, TRAPS) {
 663   VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpStrings,
 664                          _verbose.value());
 665   VMThread::execute(&dumper);
 666 }
 667 
 668 int StringtableDCmd::num_arguments() {
 669   ResourceMark rm;
 670   StringtableDCmd* dcmd = new StringtableDCmd(NULL, false);
 671   if (dcmd != NULL) {
 672     DCmdMark mark(dcmd);
 673     return dcmd->_dcmdparser.num_arguments();
 674   } else {
 675     return 0;
 676   }
 677 }
 678 
 679 #if INCLUDE_CDS_JAVA_HEAP
 680 // Sharing
 681 oop StringTable::create_archived_string(oop s, Thread* THREAD) {
 682   assert(DumpSharedSpaces, "this function is only used with -Xshare:dump");
 683 
 684   oop new_s = NULL;
 685   typeArrayOop v = java_lang_String::value_no_keepalive(s);
 686   typeArrayOop new_v = (typeArrayOop)MetaspaceShared::archive_heap_object(v, THREAD);
 687   if (new_v == NULL) {
 688     return NULL;
 689   }
 690   new_s = MetaspaceShared::archive_heap_object(s, THREAD);
 691   if (new_s == NULL) {
 692     return NULL;
 693   }
 694 
 695   // adjust the pointer to the 'value' field in the new String oop
 696   java_lang_String::set_value_raw(new_s, new_v);
 697   return new_s;
 698 }
 699 
 700 bool StringTable::copy_shared_string(GrowableArray<MemRegion> *string_space,
 701                                      CompactStringTableWriter* writer) {
 702   assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
 703 
 704   Thread* THREAD = Thread::current();
 705   G1CollectedHeap::heap()->begin_archive_alloc_range();
 706   for (int i = 0; i < the_table()->table_size(); ++i) {
 707     HashtableEntry<oop, mtSymbol>* bucket = the_table()->bucket(i);
 708     for ( ; bucket != NULL; bucket = bucket->next()) {
 709       oop s = string_object_no_keepalive(bucket);
 710       unsigned int hash = java_lang_String::hash_code(s);
 711       if (hash == 0) {
 712         continue;
 713       }
 714 
 715       java_lang_String::set_hash(s, hash);
 716       oop new_s = create_archived_string(s, THREAD);
 717       if (new_s == NULL) {
 718         continue;
 719       }
 720 
 721       // set the archived string in bucket
 722       set_string_object(bucket, new_s);
 723 
 724       // add to the compact table
 725       writer->add(hash, new_s);
 726     }
 727   }
 728 
 729   G1CollectedHeap::heap()->end_archive_alloc_range(string_space, os::vm_allocation_granularity());
 730   return true;
 731 }
 732 
 733 void StringTable::write_to_archive(GrowableArray<MemRegion> *string_space) {
 734   assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
 735 
 736   _shared_table.reset();
 737   int num_buckets = the_table()->number_of_entries() /
 738                          SharedSymbolTableBucketSize;
 739   // calculation of num_buckets can result in zero buckets, we need at least one
 740   CompactStringTableWriter writer(num_buckets > 1 ? num_buckets : 1,
 741                                   &MetaspaceShared::stats()->string);
 742 
 743   // Copy the interned strings into the "string space" within the java heap
 744   if (copy_shared_string(string_space, &writer)) {
 745     writer.dump(&_shared_table);
 746   }
 747 }
 748 
 749 void StringTable::serialize(SerializeClosure* soc) {
 750   _shared_table.set_type(CompactHashtable<oop, char>::_string_table);
 751   _shared_table.serialize(soc);
 752 
 753   if (soc->writing()) {
 754     _shared_table.reset(); // Sanity. Make sure we don't use the shared table at dump time
 755   } else if (!_shared_string_mapped) {
 756     _shared_table.reset();
 757   }
 758 }
 759 
 760 void StringTable::shared_oops_do(OopClosure* f) {
 761   _shared_table.oops_do(f);
 762 }
 763 #endif //INCLUDE_CDS_JAVA_HEAP