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