1 /* 2 * Copyright (c) 1997, 2009, 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 "incls/_precompiled.incl" 26 # include "incls/_symbolTable.cpp.incl" 27 28 // -------------------------------------------------------------------------- 29 30 SymbolTable* SymbolTable::_the_table = NULL; 31 32 // Lookup a symbol in a bucket. 33 34 symbolOop SymbolTable::lookup(int index, const char* name, 35 int len, unsigned int hash) { 36 for (HashtableEntry* e = bucket(index); e != NULL; e = e->next()) { 37 if (e->hash() == hash) { 38 symbolOop sym = symbolOop(e->literal()); 39 if (sym->equals(name, len)) { 40 return sym; 41 } 42 } 43 } 44 return NULL; 45 } 46 47 48 // We take care not to be blocking while holding the 49 // SymbolTable_lock. Otherwise, the system might deadlock, since the 50 // symboltable is used during compilation (VM_thread) The lock free 51 // synchronization is simplified by the fact that we do not delete 52 // entries in the symbol table during normal execution (only during 53 // safepoints). 54 55 symbolOop SymbolTable::lookup(const char* name, int len, TRAPS) { 56 unsigned int hashValue = hash_symbol(name, len); 57 int index = the_table()->hash_to_index(hashValue); 58 59 symbolOop s = the_table()->lookup(index, name, len, hashValue); 60 61 // Found 62 if (s != NULL) return s; 63 64 // Otherwise, add to symbol to table 65 return the_table()->basic_add(index, (u1*)name, len, hashValue, CHECK_NULL); 66 } 67 68 symbolOop SymbolTable::lookup(symbolHandle sym, int begin, int end, TRAPS) { 69 char* buffer; 70 int index, len; 71 unsigned int hashValue; 72 char* name; 73 { 74 debug_only(No_Safepoint_Verifier nsv;) 75 76 name = (char*)sym->base() + begin; 77 len = end - begin; 78 hashValue = hash_symbol(name, len); 79 index = the_table()->hash_to_index(hashValue); 80 symbolOop s = the_table()->lookup(index, name, len, hashValue); 81 82 // Found 83 if (s != NULL) return s; 84 } 85 86 // Otherwise, add to symbol to table. Copy to a C string first. 87 char stack_buf[128]; 88 ResourceMark rm(THREAD); 89 if (len <= 128) { 90 buffer = stack_buf; 91 } else { 92 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len); 93 } 94 for (int i=0; i<len; i++) { 95 buffer[i] = name[i]; 96 } 97 // Make sure there is no safepoint in the code above since name can't move. 98 // We can't include the code in No_Safepoint_Verifier because of the 99 // ResourceMark. 100 101 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, CHECK_NULL); 102 } 103 104 symbolOop SymbolTable::lookup_only(const char* name, int len, 105 unsigned int& hash) { 106 hash = hash_symbol(name, len); 107 int index = the_table()->hash_to_index(hash); 108 109 return the_table()->lookup(index, name, len, hash); 110 } 111 112 // Suggestion: Push unicode-based lookup all the way into the hashing 113 // and probing logic, so there is no need for convert_to_utf8 until 114 // an actual new symbolOop is created. 115 symbolOop SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) { 116 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length); 117 char stack_buf[128]; 118 if (utf8_length < (int) sizeof(stack_buf)) { 119 char* chars = stack_buf; 120 UNICODE::convert_to_utf8(name, utf16_length, chars); 121 return lookup(chars, utf8_length, THREAD); 122 } else { 123 ResourceMark rm(THREAD); 124 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);; 125 UNICODE::convert_to_utf8(name, utf16_length, chars); 126 return lookup(chars, utf8_length, THREAD); 127 } 128 } 129 130 symbolOop SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length, 131 unsigned int& hash) { 132 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length); 133 char stack_buf[128]; 134 if (utf8_length < (int) sizeof(stack_buf)) { 135 char* chars = stack_buf; 136 UNICODE::convert_to_utf8(name, utf16_length, chars); 137 return lookup_only(chars, utf8_length, hash); 138 } else { 139 ResourceMark rm; 140 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);; 141 UNICODE::convert_to_utf8(name, utf16_length, chars); 142 return lookup_only(chars, utf8_length, hash); 143 } 144 } 145 146 void SymbolTable::add(constantPoolHandle cp, int names_count, 147 const char** names, int* lengths, int* cp_indices, 148 unsigned int* hashValues, TRAPS) { 149 SymbolTable* table = the_table(); 150 bool added = table->basic_add(cp, names_count, names, lengths, 151 cp_indices, hashValues, CHECK); 152 if (!added) { 153 // do it the hard way 154 for (int i=0; i<names_count; i++) { 155 int index = table->hash_to_index(hashValues[i]); 156 symbolOop sym = table->basic_add(index, (u1*)names[i], lengths[i], 157 hashValues[i], CHECK); 158 cp->symbol_at_put(cp_indices[i], sym); 159 } 160 } 161 } 162 163 symbolOop SymbolTable::basic_add(int index, u1 *name, int len, 164 unsigned int hashValue, TRAPS) { 165 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(), 166 "proposed name of symbol must be stable"); 167 168 // We assume that lookup() has been called already, that it failed, 169 // and symbol was not found. We create the symbol here. 170 symbolKlass* sk = (symbolKlass*) Universe::symbolKlassObj()->klass_part(); 171 symbolOop s_oop = sk->allocate_symbol(name, len, CHECK_NULL); 172 symbolHandle sym (THREAD, s_oop); 173 174 // Allocation must be done before grapping the SymbolTable_lock lock 175 MutexLocker ml(SymbolTable_lock, THREAD); 176 177 assert(sym->equals((char*)name, len), "symbol must be properly initialized"); 178 179 // Since look-up was done lock-free, we need to check if another 180 // thread beat us in the race to insert the symbol. 181 182 symbolOop test = lookup(index, (char*)name, len, hashValue); 183 if (test != NULL) { 184 // A race occurred and another thread introduced the symbol, this one 185 // will be dropped and collected. 186 return test; 187 } 188 189 HashtableEntry* entry = new_entry(hashValue, sym()); 190 add_entry(index, entry); 191 return sym(); 192 } 193 194 bool SymbolTable::basic_add(constantPoolHandle cp, int names_count, 195 const char** names, int* lengths, 196 int* cp_indices, unsigned int* hashValues, 197 TRAPS) { 198 symbolKlass* sk = (symbolKlass*) Universe::symbolKlassObj()->klass_part(); 199 symbolOop sym_oops[symbol_alloc_batch_size]; 200 bool allocated = sk->allocate_symbols(names_count, names, lengths, 201 sym_oops, CHECK_false); 202 if (!allocated) { 203 return false; 204 } 205 symbolHandle syms[symbol_alloc_batch_size]; 206 int i; 207 for (i=0; i<names_count; i++) { 208 syms[i] = symbolHandle(THREAD, sym_oops[i]); 209 } 210 211 // Allocation must be done before grabbing the SymbolTable_lock lock 212 MutexLocker ml(SymbolTable_lock, THREAD); 213 214 for (i=0; i<names_count; i++) { 215 assert(syms[i]->equals(names[i], lengths[i]), "symbol must be properly initialized"); 216 // Since look-up was done lock-free, we need to check if another 217 // thread beat us in the race to insert the symbol. 218 int index = hash_to_index(hashValues[i]); 219 symbolOop test = lookup(index, names[i], lengths[i], hashValues[i]); 220 if (test != NULL) { 221 // A race occurred and another thread introduced the symbol, this one 222 // will be dropped and collected. Use test instead. 223 cp->symbol_at_put(cp_indices[i], test); 224 } else { 225 symbolOop sym = syms[i](); 226 HashtableEntry* entry = new_entry(hashValues[i], sym); 227 add_entry(index, entry); 228 cp->symbol_at_put(cp_indices[i], sym); 229 } 230 } 231 232 return true; 233 } 234 235 236 void SymbolTable::verify() { 237 for (int i = 0; i < the_table()->table_size(); ++i) { 238 HashtableEntry* p = the_table()->bucket(i); 239 for ( ; p != NULL; p = p->next()) { 240 symbolOop s = symbolOop(p->literal()); 241 guarantee(s != NULL, "symbol is NULL"); 242 s->verify(); 243 guarantee(s->is_perm(), "symbol not in permspace"); 244 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length()); 245 guarantee(p->hash() == h, "broken hash in symbol table entry"); 246 guarantee(the_table()->hash_to_index(h) == i, 247 "wrong index in symbol table"); 248 } 249 } 250 } 251 252 253 //--------------------------------------------------------------------------- 254 // Non-product code 255 256 #ifndef PRODUCT 257 258 void SymbolTable::print_histogram() { 259 MutexLocker ml(SymbolTable_lock); 260 const int results_length = 100; 261 int results[results_length]; 262 int i,j; 263 264 // initialize results to zero 265 for (j = 0; j < results_length; j++) { 266 results[j] = 0; 267 } 268 269 int total = 0; 270 int max_symbols = 0; 271 int out_of_range = 0; 272 for (i = 0; i < the_table()->table_size(); i++) { 273 HashtableEntry* p = the_table()->bucket(i); 274 for ( ; p != NULL; p = p->next()) { 275 int counter = symbolOop(p->literal())->utf8_length(); 276 total += counter; 277 if (counter < results_length) { 278 results[counter]++; 279 } else { 280 out_of_range++; 281 } 282 max_symbols = MAX2(max_symbols, counter); 283 } 284 } 285 tty->print_cr("Symbol Table:"); 286 tty->print_cr("%8s %5d", "Total ", total); 287 tty->print_cr("%8s %5d", "Maximum", max_symbols); 288 tty->print_cr("%8s %3.2f", "Average", 289 ((float) total / (float) the_table()->table_size())); 290 tty->print_cr("%s", "Histogram:"); 291 tty->print_cr(" %s %29s", "Length", "Number chains that length"); 292 for (i = 0; i < results_length; i++) { 293 if (results[i] > 0) { 294 tty->print_cr("%6d %10d", i, results[i]); 295 } 296 } 297 int line_length = 70; 298 tty->print_cr("%s %30s", " Length", "Number chains that length"); 299 for (i = 0; i < results_length; i++) { 300 if (results[i] > 0) { 301 tty->print("%4d", i); 302 for (j = 0; (j < results[i]) && (j < line_length); j++) { 303 tty->print("%1s", "*"); 304 } 305 if (j == line_length) { 306 tty->print("%1s", "+"); 307 } 308 tty->cr(); 309 } 310 } 311 tty->print_cr(" %s %d: %d\n", "Number chains longer than", 312 results_length, out_of_range); 313 } 314 315 #endif // PRODUCT 316 317 // -------------------------------------------------------------------------- 318 319 #ifdef ASSERT 320 class StableMemoryChecker : public StackObj { 321 enum { _bufsize = wordSize*4 }; 322 323 address _region; 324 jint _size; 325 u1 _save_buf[_bufsize]; 326 327 int sample(u1* save_buf) { 328 if (_size <= _bufsize) { 329 memcpy(save_buf, _region, _size); 330 return _size; 331 } else { 332 // copy head and tail 333 memcpy(&save_buf[0], _region, _bufsize/2); 334 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2); 335 return (_bufsize/2)*2; 336 } 337 } 338 339 public: 340 StableMemoryChecker(const void* region, jint size) { 341 _region = (address) region; 342 _size = size; 343 sample(_save_buf); 344 } 345 346 bool verify() { 347 u1 check_buf[sizeof(_save_buf)]; 348 int check_size = sample(check_buf); 349 return (0 == memcmp(_save_buf, check_buf, check_size)); 350 } 351 352 void set_region(const void* region) { _region = (address) region; } 353 }; 354 #endif 355 356 357 // -------------------------------------------------------------------------- 358 359 360 // Compute the hash value for a java.lang.String object which would 361 // contain the characters passed in. This hash value is used for at 362 // least two purposes. 363 // 364 // (a) As the hash value used by the StringTable for bucket selection 365 // and comparison (stored in the HashtableEntry structures). This 366 // is used in the String.intern() method. 367 // 368 // (b) As the hash value used by the String object itself, in 369 // String.hashCode(). This value is normally calculate in Java code 370 // in the String.hashCode method(), but is precomputed for String 371 // objects in the shared archive file. 372 // 373 // For this reason, THIS ALGORITHM MUST MATCH String.hashCode(). 374 375 int StringTable::hash_string(jchar* s, int len) { 376 unsigned h = 0; 377 while (len-- > 0) { 378 h = 31*h + (unsigned) *s; 379 s++; 380 } 381 return h; 382 } 383 384 385 StringTable* StringTable::_the_table = NULL; 386 387 oop StringTable::lookup(int index, jchar* name, 388 int len, unsigned int hash) { 389 for (HashtableEntry* l = bucket(index); l != NULL; l = l->next()) { 390 if (l->hash() == hash) { 391 if (java_lang_String::equals(l->literal(), name, len)) { 392 return l->literal(); 393 } 394 } 395 } 396 return NULL; 397 } 398 399 400 oop StringTable::basic_add(int index, Handle string_or_null, jchar* name, 401 int len, unsigned int hashValue, TRAPS) { 402 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0]))); 403 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(), 404 "proposed name of symbol must be stable"); 405 406 Handle string; 407 // try to reuse the string if possible 408 if (!string_or_null.is_null() && string_or_null()->is_perm()) { 409 string = string_or_null; 410 } else { 411 string = java_lang_String::create_tenured_from_unicode(name, len, CHECK_NULL); 412 } 413 414 // Allocation must be done before grapping the SymbolTable_lock lock 415 MutexLocker ml(StringTable_lock, THREAD); 416 417 assert(java_lang_String::equals(string(), name, len), 418 "string must be properly initialized"); 419 420 // Since look-up was done lock-free, we need to check if another 421 // thread beat us in the race to insert the symbol. 422 423 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int) 424 if (test != NULL) { 425 // Entry already added 426 return test; 427 } 428 429 HashtableEntry* entry = new_entry(hashValue, string()); 430 add_entry(index, entry); 431 return string(); 432 } 433 434 435 oop StringTable::lookup(symbolOop symbol) { 436 ResourceMark rm; 437 int length; 438 jchar* chars = symbol->as_unicode(length); 439 unsigned int hashValue = hash_string(chars, length); 440 int index = the_table()->hash_to_index(hashValue); 441 return the_table()->lookup(index, chars, length, hashValue); 442 } 443 444 445 oop StringTable::intern(Handle string_or_null, jchar* name, 446 int len, TRAPS) { 447 unsigned int hashValue = hash_string(name, len); 448 int index = the_table()->hash_to_index(hashValue); 449 oop string = the_table()->lookup(index, name, len, hashValue); 450 451 // Found 452 if (string != NULL) return string; 453 454 // Otherwise, add to symbol to table 455 return the_table()->basic_add(index, string_or_null, name, len, 456 hashValue, CHECK_NULL); 457 } 458 459 oop StringTable::intern(symbolOop symbol, TRAPS) { 460 if (symbol == NULL) return NULL; 461 ResourceMark rm(THREAD); 462 int length; 463 jchar* chars = symbol->as_unicode(length); 464 Handle string; 465 oop result = intern(string, chars, length, CHECK_NULL); 466 return result; 467 } 468 469 470 oop StringTable::intern(oop string, TRAPS) 471 { 472 if (string == NULL) return NULL; 473 ResourceMark rm(THREAD); 474 int length; 475 Handle h_string (THREAD, string); 476 jchar* chars = java_lang_String::as_unicode_string(string, length); 477 oop result = intern(h_string, chars, length, CHECK_NULL); 478 return result; 479 } 480 481 482 oop StringTable::intern(const char* utf8_string, TRAPS) { 483 if (utf8_string == NULL) return NULL; 484 ResourceMark rm(THREAD); 485 int length = UTF8::unicode_length(utf8_string); 486 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length); 487 UTF8::convert_to_unicode(utf8_string, chars, length); 488 Handle string; 489 oop result = intern(string, chars, length, CHECK_NULL); 490 return result; 491 } 492 493 void StringTable::verify() { 494 for (int i = 0; i < the_table()->table_size(); ++i) { 495 HashtableEntry* p = the_table()->bucket(i); 496 for ( ; p != NULL; p = p->next()) { 497 oop s = p->literal(); 498 guarantee(s != NULL, "interned string is NULL"); 499 guarantee(s->is_perm(), "interned string not in permspace"); 500 501 int length; 502 jchar* chars = java_lang_String::as_unicode_string(s, length); 503 unsigned int h = hash_string(chars, length); 504 guarantee(p->hash() == h, "broken hash in string table entry"); 505 guarantee(the_table()->hash_to_index(h) == i, 506 "wrong index in string table"); 507 } 508 } 509 }