symbolTable.cpp revision 3465:d2a62e0f25eb
1/* 2 * Copyright (c) 1997, 2012, 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#include "utilities/numberSeq.hpp" 39 40// -------------------------------------------------------------------------- 41 42SymbolTable* SymbolTable::_the_table = NULL; 43// Static arena for symbols that are not deallocated 44Arena* SymbolTable::_arena = NULL; 45bool SymbolTable::_needs_rehashing = false; 46jint SymbolTable::_seed = 0; 47 48Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) { 49 assert (len <= Symbol::max_length(), "should be checked by caller"); 50 51 Symbol* sym; 52 // Allocate symbols in the C heap when dumping shared spaces in case there 53 // are temporary symbols we can remove. 54 if (c_heap || DumpSharedSpaces) { 55 // refcount starts as 1 56 sym = new (len, THREAD) Symbol(name, len, 1); 57 } else { 58 sym = new (len, arena(), THREAD) Symbol(name, len, -1); 59 } 60 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted"); 61 return sym; 62} 63 64void SymbolTable::initialize_symbols(int arena_alloc_size) { 65 // Initialize the arena for global symbols, size passed in depends on CDS. 66 if (arena_alloc_size == 0) { 67 _arena = new (mtSymbol) Arena(); 68 } else { 69 _arena = new (mtSymbol) Arena(arena_alloc_size); 70 } 71} 72 73// Call function for all symbols in the symbol table. 74void SymbolTable::symbols_do(SymbolClosure *cl) { 75 const int n = the_table()->table_size(); 76 for (int i = 0; i < n; i++) { 77 for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i); 78 p != NULL; 79 p = p->next()) { 80 cl->do_symbol(p->literal_addr()); 81 } 82 } 83} 84 85int SymbolTable::symbols_removed = 0; 86int SymbolTable::symbols_counted = 0; 87 88// Remove unreferenced symbols from the symbol table 89// This is done late during GC. 90void SymbolTable::unlink() { 91 int removed = 0; 92 int total = 0; 93 size_t memory_total = 0; 94 for (int i = 0; i < the_table()->table_size(); ++i) { 95 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i); 96 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i); 97 while (entry != NULL) { 98 // Shared entries are normally at the end of the bucket and if we run into 99 // a shared entry, then there is nothing more to remove. However, if we 100 // have rehashed the table, then the shared entries are no longer at the 101 // end of the bucket. 102 if (entry->is_shared() && !use_alternate_hashcode()) { 103 break; 104 } 105 Symbol* s = entry->literal(); 106 memory_total += s->object_size(); 107 total++; 108 assert(s != NULL, "just checking"); 109 // If reference count is zero, remove. 110 if (s->refcount() == 0) { 111 assert(!entry->is_shared(), "shared entries should be kept live"); 112 delete s; 113 removed++; 114 *p = entry->next(); 115 the_table()->free_entry(entry); 116 } else { 117 p = entry->next_addr(); 118 } 119 // get next entry 120 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p); 121 } 122 } 123 symbols_removed += removed; 124 symbols_counted += total; 125 // Exclude printing for normal PrintGCDetails because people parse 126 // this output. 127 if (PrintGCDetails && Verbose && WizardMode) { 128 gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", total, 129 (memory_total*HeapWordSize)/1024); 130 } 131} 132 133unsigned int SymbolTable::new_hash(Symbol* sym) { 134 ResourceMark rm; 135 // Use alternate hashing algorithm on this symbol. 136 return AltHashing::murmur3_32(seed(), (const jbyte*)sym->as_C_string(), sym->utf8_length()); 137} 138 139// Create a new table and using alternate hash code, populate the new table 140// with the existing strings. Set flag to use the alternate hash code afterwards. 141void SymbolTable::rehash_table() { 142 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 143 // This should never happen with -Xshare:dump but it might in testing mode. 144 if (DumpSharedSpaces) return; 145 // Create a new symbol table 146 SymbolTable* new_table = new SymbolTable(); 147 148 // Initialize the global seed for hashing. 149 _seed = AltHashing::compute_seed(); 150 assert(seed() != 0, "shouldn't be zero"); 151 152 the_table()->move_to(new_table); 153 154 // Delete the table and buckets (entries are reused in new table). 155 delete _the_table; 156 // Don't check if we need rehashing until the table gets unbalanced again. 157 // Then rehash with a new global seed. 158 _needs_rehashing = false; 159 _the_table = new_table; 160} 161 162// Lookup a symbol in a bucket. 163 164Symbol* SymbolTable::lookup(int index, const char* name, 165 int len, unsigned int hash) { 166 int count = 0; 167 for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) { 168 count++; // count all entries in this bucket, not just ones with same hash 169 if (e->hash() == hash) { 170 Symbol* sym = e->literal(); 171 if (sym->equals(name, len)) { 172 // something is referencing this symbol now. 173 sym->increment_refcount(); 174 return sym; 175 } 176 } 177 } 178 // If the bucket size is too deep check if this hash code is insufficient. 179 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) { 180 _needs_rehashing = check_rehash_table(count); 181 } 182 return NULL; 183} 184 185// Pick hashing algorithm. 186unsigned int SymbolTable::hash_symbol(const char* s, int len) { 187 return use_alternate_hashcode() ? 188 AltHashing::murmur3_32(seed(), (const jbyte*)s, len) : 189 java_lang_String::to_hash(s, len); 190} 191 192 193// We take care not to be blocking while holding the 194// SymbolTable_lock. Otherwise, the system might deadlock, since the 195// symboltable is used during compilation (VM_thread) The lock free 196// synchronization is simplified by the fact that we do not delete 197// entries in the symbol table during normal execution (only during 198// safepoints). 199 200Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) { 201 unsigned int hashValue = hash_symbol(name, len); 202 int index = the_table()->hash_to_index(hashValue); 203 204 Symbol* s = the_table()->lookup(index, name, len, hashValue); 205 206 // Found 207 if (s != NULL) return s; 208 209 // Grab SymbolTable_lock first. 210 MutexLocker ml(SymbolTable_lock, THREAD); 211 212 // Otherwise, add to symbol to table 213 return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL); 214} 215 216Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) { 217 char* buffer; 218 int index, len; 219 unsigned int hashValue; 220 char* name; 221 { 222 debug_only(No_Safepoint_Verifier nsv;) 223 224 name = (char*)sym->base() + begin; 225 len = end - begin; 226 hashValue = hash_symbol(name, len); 227 index = the_table()->hash_to_index(hashValue); 228 Symbol* s = the_table()->lookup(index, name, len, hashValue); 229 230 // Found 231 if (s != NULL) return s; 232 } 233 234 // Otherwise, add to symbol to table. Copy to a C string first. 235 char stack_buf[128]; 236 ResourceMark rm(THREAD); 237 if (len <= 128) { 238 buffer = stack_buf; 239 } else { 240 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len); 241 } 242 for (int i=0; i<len; i++) { 243 buffer[i] = name[i]; 244 } 245 // Make sure there is no safepoint in the code above since name can't move. 246 // We can't include the code in No_Safepoint_Verifier because of the 247 // ResourceMark. 248 249 // Grab SymbolTable_lock first. 250 MutexLocker ml(SymbolTable_lock, THREAD); 251 252 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL); 253} 254 255Symbol* SymbolTable::lookup_only(const char* name, int len, 256 unsigned int& hash) { 257 hash = hash_symbol(name, len); 258 int index = the_table()->hash_to_index(hash); 259 260 Symbol* s = the_table()->lookup(index, name, len, hash); 261 return s; 262} 263 264// Look up the address of the literal in the SymbolTable for this Symbol* 265// Do not create any new symbols 266// Do not increment the reference count to keep this alive 267Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){ 268 unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length()); 269 int index = the_table()->hash_to_index(hash); 270 271 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) { 272 if (e->hash() == hash) { 273 Symbol* literal_sym = e->literal(); 274 if (sym == literal_sym) { 275 return e->literal_addr(); 276 } 277 } 278 } 279 return NULL; 280} 281 282// Suggestion: Push unicode-based lookup all the way into the hashing 283// and probing logic, so there is no need for convert_to_utf8 until 284// an actual new Symbol* is created. 285Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) { 286 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length); 287 char stack_buf[128]; 288 if (utf8_length < (int) sizeof(stack_buf)) { 289 char* chars = stack_buf; 290 UNICODE::convert_to_utf8(name, utf16_length, chars); 291 return lookup(chars, utf8_length, THREAD); 292 } else { 293 ResourceMark rm(THREAD); 294 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);; 295 UNICODE::convert_to_utf8(name, utf16_length, chars); 296 return lookup(chars, utf8_length, THREAD); 297 } 298} 299 300Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length, 301 unsigned int& hash) { 302 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length); 303 char stack_buf[128]; 304 if (utf8_length < (int) sizeof(stack_buf)) { 305 char* chars = stack_buf; 306 UNICODE::convert_to_utf8(name, utf16_length, chars); 307 return lookup_only(chars, utf8_length, hash); 308 } else { 309 ResourceMark rm; 310 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);; 311 UNICODE::convert_to_utf8(name, utf16_length, chars); 312 return lookup_only(chars, utf8_length, hash); 313 } 314} 315 316void SymbolTable::add(Handle class_loader, constantPoolHandle cp, 317 int names_count, 318 const char** names, int* lengths, int* cp_indices, 319 unsigned int* hashValues, TRAPS) { 320 // Grab SymbolTable_lock first. 321 MutexLocker ml(SymbolTable_lock, THREAD); 322 323 SymbolTable* table = the_table(); 324 bool added = table->basic_add(class_loader, cp, names_count, names, lengths, 325 cp_indices, hashValues, CHECK); 326 if (!added) { 327 // do it the hard way 328 for (int i=0; i<names_count; i++) { 329 int index = table->hash_to_index(hashValues[i]); 330 bool c_heap = class_loader() != NULL; 331 Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK); 332 cp->symbol_at_put(cp_indices[i], sym); 333 } 334 } 335} 336 337Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) { 338 unsigned int hash; 339 Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash); 340 if (result != NULL) { 341 return result; 342 } 343 // Grab SymbolTable_lock first. 344 MutexLocker ml(SymbolTable_lock, THREAD); 345 346 SymbolTable* table = the_table(); 347 int index = table->hash_to_index(hash); 348 return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD); 349} 350 351Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len, 352 unsigned int hashValue_arg, bool c_heap, TRAPS) { 353 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(), 354 "proposed name of symbol must be stable"); 355 356 // Don't allow symbols to be created which cannot fit in a Symbol*. 357 if (len > Symbol::max_length()) { 358 THROW_MSG_0(vmSymbols::java_lang_InternalError(), 359 "name is too long to represent"); 360 } 361 362 // Cannot hit a safepoint in this function because the "this" pointer can move. 363 No_Safepoint_Verifier nsv; 364 365 // Check if the symbol table has been rehashed, if so, need to recalculate 366 // the hash value and index. 367 unsigned int hashValue; 368 int index; 369 if (use_alternate_hashcode()) { 370 hashValue = hash_symbol((const char*)name, len); 371 index = hash_to_index(hashValue); 372 } else { 373 hashValue = hashValue_arg; 374 index = index_arg; 375 } 376 377 // Since look-up was done lock-free, we need to check if another 378 // thread beat us in the race to insert the symbol. 379 Symbol* test = lookup(index, (char*)name, len, hashValue); 380 if (test != NULL) { 381 // A race occurred and another thread introduced the symbol. 382 assert(test->refcount() != 0, "lookup should have incremented the count"); 383 return test; 384 } 385 386 // Create a new symbol. 387 Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL); 388 assert(sym->equals((char*)name, len), "symbol must be properly initialized"); 389 390 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym); 391 add_entry(index, entry); 392 return sym; 393} 394 395// This version of basic_add adds symbols in batch from the constant pool 396// parsing. 397bool SymbolTable::basic_add(Handle class_loader, constantPoolHandle cp, 398 int names_count, 399 const char** names, int* lengths, 400 int* cp_indices, unsigned int* hashValues, 401 TRAPS) { 402 403 // Check symbol names are not too long. If any are too long, don't add any. 404 for (int i = 0; i< names_count; i++) { 405 if (lengths[i] > Symbol::max_length()) { 406 THROW_MSG_0(vmSymbols::java_lang_InternalError(), 407 "name is too long to represent"); 408 } 409 } 410 411 // Cannot hit a safepoint in this function because the "this" pointer can move. 412 No_Safepoint_Verifier nsv; 413 414 for (int i=0; i<names_count; i++) { 415 // Check if the symbol table has been rehashed, if so, need to recalculate 416 // the hash value. 417 unsigned int hashValue; 418 if (use_alternate_hashcode()) { 419 hashValue = hash_symbol(names[i], lengths[i]); 420 } else { 421 hashValue = hashValues[i]; 422 } 423 // Since look-up was done lock-free, we need to check if another 424 // thread beat us in the race to insert the symbol. 425 int index = hash_to_index(hashValue); 426 Symbol* test = lookup(index, names[i], lengths[i], hashValue); 427 if (test != NULL) { 428 // A race occurred and another thread introduced the symbol, this one 429 // will be dropped and collected. Use test instead. 430 cp->symbol_at_put(cp_indices[i], test); 431 assert(test->refcount() != 0, "lookup should have incremented the count"); 432 } else { 433 // Create a new symbol. The null class loader is never unloaded so these 434 // are allocated specially in a permanent arena. 435 bool c_heap = class_loader() != NULL; 436 Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false)); 437 assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized"); // why wouldn't it be??? 438 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym); 439 add_entry(index, entry); 440 cp->symbol_at_put(cp_indices[i], sym); 441 } 442 } 443 return true; 444} 445 446 447void SymbolTable::verify() { 448 for (int i = 0; i < the_table()->table_size(); ++i) { 449 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i); 450 for ( ; p != NULL; p = p->next()) { 451 Symbol* s = (Symbol*)(p->literal()); 452 guarantee(s != NULL, "symbol is NULL"); 453 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length()); 454 guarantee(p->hash() == h, "broken hash in symbol table entry"); 455 guarantee(the_table()->hash_to_index(h) == i, 456 "wrong index in symbol table"); 457 } 458 } 459} 460 461void SymbolTable::dump(outputStream* st) { 462 NumberSeq summary; 463 for (int i = 0; i < the_table()->table_size(); ++i) { 464 int count = 0; 465 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(i); 466 e != NULL; e = e->next()) { 467 count++; 468 } 469 summary.add((double)count); 470 } 471 st->print_cr("SymbolTable statistics:"); 472 st->print_cr("Number of buckets : %7d", summary.num()); 473 st->print_cr("Average bucket size : %7.0f", summary.avg()); 474 st->print_cr("Variance of bucket size : %7.0f", summary.variance()); 475 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd()); 476 st->print_cr("Maximum bucket size : %7.0f", summary.maximum()); 477} 478 479 480//--------------------------------------------------------------------------- 481// Non-product code 482 483#ifndef PRODUCT 484 485void SymbolTable::print_histogram() { 486 MutexLocker ml(SymbolTable_lock); 487 const int results_length = 100; 488 int results[results_length]; 489 int i,j; 490 491 // initialize results to zero 492 for (j = 0; j < results_length; j++) { 493 results[j] = 0; 494 } 495 496 int total = 0; 497 int max_symbols = 0; 498 int out_of_range = 0; 499 int memory_total = 0; 500 int count = 0; 501 for (i = 0; i < the_table()->table_size(); i++) { 502 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i); 503 for ( ; p != NULL; p = p->next()) { 504 memory_total += p->literal()->object_size(); 505 count++; 506 int counter = p->literal()->utf8_length(); 507 total += counter; 508 if (counter < results_length) { 509 results[counter]++; 510 } else { 511 out_of_range++; 512 } 513 max_symbols = MAX2(max_symbols, counter); 514 } 515 } 516 tty->print_cr("Symbol Table:"); 517 tty->print_cr("Total number of symbols %5d", count); 518 tty->print_cr("Total size in memory %5dK", 519 (memory_total*HeapWordSize)/1024); 520 tty->print_cr("Total counted %5d", symbols_counted); 521 tty->print_cr("Total removed %5d", symbols_removed); 522 if (symbols_counted > 0) { 523 tty->print_cr("Percent removed %3.2f", 524 ((float)symbols_removed/(float)symbols_counted)* 100); 525 } 526 tty->print_cr("Reference counts %5d", Symbol::_total_count); 527 tty->print_cr("Symbol arena size %5d used %5d", 528 arena()->size_in_bytes(), arena()->used()); 529 tty->print_cr("Histogram of symbol length:"); 530 tty->print_cr("%8s %5d", "Total ", total); 531 tty->print_cr("%8s %5d", "Maximum", max_symbols); 532 tty->print_cr("%8s %3.2f", "Average", 533 ((float) total / (float) the_table()->table_size())); 534 tty->print_cr("%s", "Histogram:"); 535 tty->print_cr(" %s %29s", "Length", "Number chains that length"); 536 for (i = 0; i < results_length; i++) { 537 if (results[i] > 0) { 538 tty->print_cr("%6d %10d", i, results[i]); 539 } 540 } 541 if (Verbose) { 542 int line_length = 70; 543 tty->print_cr("%s %30s", " Length", "Number chains that length"); 544 for (i = 0; i < results_length; i++) { 545 if (results[i] > 0) { 546 tty->print("%4d", i); 547 for (j = 0; (j < results[i]) && (j < line_length); j++) { 548 tty->print("%1s", "*"); 549 } 550 if (j == line_length) { 551 tty->print("%1s", "+"); 552 } 553 tty->cr(); 554 } 555 } 556 } 557 tty->print_cr(" %s %d: %d\n", "Number chains longer than", 558 results_length, out_of_range); 559} 560 561void SymbolTable::print() { 562 for (int i = 0; i < the_table()->table_size(); ++i) { 563 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i); 564 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i); 565 if (entry != NULL) { 566 while (entry != NULL) { 567 tty->print(PTR_FORMAT " ", entry->literal()); 568 entry->literal()->print(); 569 tty->print(" %d", entry->literal()->refcount()); 570 p = entry->next_addr(); 571 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p); 572 } 573 tty->cr(); 574 } 575 } 576} 577#endif // PRODUCT 578 579// -------------------------------------------------------------------------- 580 581#ifdef ASSERT 582class StableMemoryChecker : public StackObj { 583 enum { _bufsize = wordSize*4 }; 584 585 address _region; 586 jint _size; 587 u1 _save_buf[_bufsize]; 588 589 int sample(u1* save_buf) { 590 if (_size <= _bufsize) { 591 memcpy(save_buf, _region, _size); 592 return _size; 593 } else { 594 // copy head and tail 595 memcpy(&save_buf[0], _region, _bufsize/2); 596 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2); 597 return (_bufsize/2)*2; 598 } 599 } 600 601 public: 602 StableMemoryChecker(const void* region, jint size) { 603 _region = (address) region; 604 _size = size; 605 sample(_save_buf); 606 } 607 608 bool verify() { 609 u1 check_buf[sizeof(_save_buf)]; 610 int check_size = sample(check_buf); 611 return (0 == memcmp(_save_buf, check_buf, check_size)); 612 } 613 614 void set_region(const void* region) { _region = (address) region; } 615}; 616#endif 617 618 619// -------------------------------------------------------------------------- 620StringTable* StringTable::_the_table = NULL; 621 622bool StringTable::_needs_rehashing = false; 623jint StringTable::_seed = 0; 624 625// Pick hashing algorithm 626unsigned int StringTable::hash_string(const jchar* s, int len) { 627 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) : 628 java_lang_String::to_hash(s, len); 629} 630 631oop StringTable::lookup(int index, jchar* name, 632 int len, unsigned int hash) { 633 int count = 0; 634 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) { 635 count++; 636 if (l->hash() == hash) { 637 if (java_lang_String::equals(l->literal(), name, len)) { 638 return l->literal(); 639 } 640 } 641 } 642 // If the bucket size is too deep check if this hash code is insufficient. 643 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) { 644 _needs_rehashing = check_rehash_table(count); 645 } 646 return NULL; 647} 648 649 650oop StringTable::basic_add(int index_arg, Handle string, jchar* name, 651 int len, unsigned int hashValue_arg, TRAPS) { 652 653 assert(java_lang_String::equals(string(), name, len), 654 "string must be properly initialized"); 655 // Cannot hit a safepoint in this function because the "this" pointer can move. 656 No_Safepoint_Verifier nsv; 657 658 // Check if the symbol table has been rehashed, if so, need to recalculate 659 // the hash value and index before second lookup. 660 unsigned int hashValue; 661 int index; 662 if (use_alternate_hashcode()) { 663 hashValue = hash_string(name, len); 664 index = hash_to_index(hashValue); 665 } else { 666 hashValue = hashValue_arg; 667 index = index_arg; 668 } 669 670 // Since look-up was done lock-free, we need to check if another 671 // thread beat us in the race to insert the symbol. 672 673 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int) 674 if (test != NULL) { 675 // Entry already added 676 return test; 677 } 678 679 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string()); 680 add_entry(index, entry); 681 return string(); 682} 683 684 685oop StringTable::lookup(Symbol* symbol) { 686 ResourceMark rm; 687 int length; 688 jchar* chars = symbol->as_unicode(length); 689 unsigned int hashValue = hash_string(chars, length); 690 int index = the_table()->hash_to_index(hashValue); 691 return the_table()->lookup(index, chars, length, hashValue); 692} 693 694 695oop StringTable::intern(Handle string_or_null, jchar* name, 696 int len, TRAPS) { 697 unsigned int hashValue = hash_string(name, len); 698 int index = the_table()->hash_to_index(hashValue); 699 oop found_string = the_table()->lookup(index, name, len, hashValue); 700 701 // Found 702 if (found_string != NULL) return found_string; 703 704 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0]))); 705 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(), 706 "proposed name of symbol must be stable"); 707 708 Handle string; 709 // try to reuse the string if possible 710 if (!string_or_null.is_null() && (!JavaObjectsInPerm || string_or_null()->is_perm())) { 711 string = string_or_null; 712 } else { 713 string = java_lang_String::create_tenured_from_unicode(name, len, CHECK_NULL); 714 } 715 716 // Grab the StringTable_lock before getting the_table() because it could 717 // change at safepoint. 718 MutexLocker ml(StringTable_lock, THREAD); 719 720 // Otherwise, add to symbol to table 721 return the_table()->basic_add(index, string, name, len, 722 hashValue, CHECK_NULL); 723} 724 725oop StringTable::intern(Symbol* symbol, TRAPS) { 726 if (symbol == NULL) return NULL; 727 ResourceMark rm(THREAD); 728 int length; 729 jchar* chars = symbol->as_unicode(length); 730 Handle string; 731 oop result = intern(string, chars, length, CHECK_NULL); 732 return result; 733} 734 735 736oop StringTable::intern(oop string, TRAPS) 737{ 738 if (string == NULL) return NULL; 739 ResourceMark rm(THREAD); 740 int length; 741 Handle h_string (THREAD, string); 742 jchar* chars = java_lang_String::as_unicode_string(string, length); 743 oop result = intern(h_string, chars, length, CHECK_NULL); 744 return result; 745} 746 747 748oop StringTable::intern(const char* utf8_string, TRAPS) { 749 if (utf8_string == NULL) return NULL; 750 ResourceMark rm(THREAD); 751 int length = UTF8::unicode_length(utf8_string); 752 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length); 753 UTF8::convert_to_unicode(utf8_string, chars, length); 754 Handle string; 755 oop result = intern(string, chars, length, CHECK_NULL); 756 return result; 757} 758 759void StringTable::unlink(BoolObjectClosure* is_alive) { 760 // Readers of the table are unlocked, so we should only be removing 761 // entries at a safepoint. 762 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 763 for (int i = 0; i < the_table()->table_size(); ++i) { 764 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i); 765 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i); 766 while (entry != NULL) { 767 // Shared entries are normally at the end of the bucket and if we run into 768 // a shared entry, then there is nothing more to remove. However, if we 769 // have rehashed the table, then the shared entries are no longer at the 770 // end of the bucket. 771 if (entry->is_shared() && !use_alternate_hashcode()) { 772 break; 773 } 774 assert(entry->literal() != NULL, "just checking"); 775 if (entry->is_shared() || is_alive->do_object_b(entry->literal())) { 776 p = entry->next_addr(); 777 } else { 778 *p = entry->next(); 779 the_table()->free_entry(entry); 780 } 781 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p); 782 } 783 } 784} 785 786void StringTable::oops_do(OopClosure* f) { 787 for (int i = 0; i < the_table()->table_size(); ++i) { 788 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i); 789 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i); 790 while (entry != NULL) { 791 f->do_oop((oop*)entry->literal_addr()); 792 793 // Did the closure remove the literal from the table? 794 if (entry->literal() == NULL) { 795 assert(!entry->is_shared(), "immutable hashtable entry?"); 796 *p = entry->next(); 797 the_table()->free_entry(entry); 798 } else { 799 p = entry->next_addr(); 800 } 801 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p); 802 } 803 } 804} 805 806void StringTable::verify() { 807 for (int i = 0; i < the_table()->table_size(); ++i) { 808 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i); 809 for ( ; p != NULL; p = p->next()) { 810 oop s = p->literal(); 811 guarantee(s != NULL, "interned string is NULL"); 812 guarantee(s->is_perm() || !JavaObjectsInPerm, "interned string not in permspace"); 813 unsigned int h = java_lang_String::hash_string(s); 814 guarantee(p->hash() == h, "broken hash in string table entry"); 815 guarantee(the_table()->hash_to_index(h) == i, 816 "wrong index in string table"); 817 } 818 } 819} 820 821void StringTable::dump(outputStream* st) { 822 NumberSeq summary; 823 for (int i = 0; i < the_table()->table_size(); ++i) { 824 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i); 825 int count = 0; 826 for ( ; p != NULL; p = p->next()) { 827 count++; 828 } 829 summary.add((double)count); 830 } 831 st->print_cr("StringTable statistics:"); 832 st->print_cr("Number of buckets : %7d", summary.num()); 833 st->print_cr("Average bucket size : %7.0f", summary.avg()); 834 st->print_cr("Variance of bucket size : %7.0f", summary.variance()); 835 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd()); 836 st->print_cr("Maximum bucket size : %7.0f", summary.maximum()); 837} 838 839 840unsigned int StringTable::new_hash(oop string) { 841 ResourceMark rm; 842 int length; 843 jchar* chars = java_lang_String::as_unicode_string(string, length); 844 // Use alternate hashing algorithm on the string 845 return AltHashing::murmur3_32(seed(), chars, length); 846} 847 848// Create a new table and using alternate hash code, populate the new table 849// with the existing strings. Set flag to use the alternate hash code afterwards. 850void StringTable::rehash_table() { 851 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 852 // This should never happen with -Xshare:dump but it might in testing mode. 853 if (DumpSharedSpaces) return; 854 StringTable* new_table = new StringTable(); 855 856 // Initialize new global seed for hashing. 857 _seed = AltHashing::compute_seed(); 858 assert(seed() != 0, "shouldn't be zero"); 859 860 // Rehash the table 861 the_table()->move_to(new_table); 862 863 // Delete the table and buckets (entries are reused in new table). 864 delete _the_table; 865 // Don't check if we need rehashing until the table gets unbalanced again. 866 // Then rehash with a new global seed. 867 _needs_rehashing = false; 868 _the_table = new_table; 869} 870