1 /*
2 * Copyright (c) 1997, 2013, 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
39 // --------------------------------------------------------------------------
40
41 SymbolTable* SymbolTable::_the_table = NULL;
42 // Static arena for symbols that are not deallocated
43 Arena* SymbolTable::_arena = NULL;
44 bool SymbolTable::_needs_rehashing = false;
45
46 Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) {
47 assert (len <= Symbol::max_length(), "should be checked by caller");
48
49 Symbol* sym;
50
51 if (DumpSharedSpaces) {
52 // Allocate all symbols to CLD shared metaspace
53 sym = new (len, ClassLoaderData::the_null_class_loader_data(), THREAD) Symbol(name, len, -1);
54 } else if (c_heap) {
55 // refcount starts as 1
56 sym = new (len, THREAD) Symbol(name, len, 1);
57 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
58 } else {
59 // Allocate to global arena
60 sym = new (len, arena(), THREAD) Symbol(name, len, -1);
61 }
62 return sym;
63 }
64
65 void SymbolTable::initialize_symbols(int arena_alloc_size) {
66 // Initialize the arena for global symbols, size passed in depends on CDS.
67 if (arena_alloc_size == 0) {
68 _arena = new (mtSymbol) Arena();
69 } else {
70 _arena = new (mtSymbol) Arena(arena_alloc_size);
71 }
72 }
73
74 // Call function for all symbols in the symbol table.
75 void SymbolTable::symbols_do(SymbolClosure *cl) {
76 const int n = the_table()->table_size();
77 for (int i = 0; i < n; i++) {
78 for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
79 p != NULL;
80 p = p->next()) {
81 cl->do_symbol(p->literal_addr());
82 }
83 }
84 }
85
86 int SymbolTable::symbols_removed = 0;
87 int SymbolTable::symbols_counted = 0;
88
89 // Remove unreferenced symbols from the symbol table
90 // This is done late during GC.
91 void SymbolTable::unlink() {
92 int removed = 0;
93 int total = 0;
94 size_t memory_total = 0;
95 for (int i = 0; i < the_table()->table_size(); ++i) {
96 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
97 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
98 while (entry != NULL) {
99 // Shared entries are normally at the end of the bucket and if we run into
100 // a shared entry, then there is nothing more to remove. However, if we
101 // have rehashed the table, then the shared entries are no longer at the
102 // end of the bucket.
103 if (entry->is_shared() && !use_alternate_hashcode()) {
104 break;
105 }
106 Symbol* s = entry->literal();
107 memory_total += s->size();
108 total++;
109 assert(s != NULL, "just checking");
110 // If reference count is zero, remove.
111 if (s->refcount() == 0) {
112 assert(!entry->is_shared(), "shared entries should be kept live");
113 delete s;
114 removed++;
115 *p = entry->next();
116 the_table()->free_entry(entry);
117 } else {
118 p = entry->next_addr();
119 }
120 // get next entry
121 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
122 }
123 }
124 symbols_removed += removed;
125 symbols_counted += total;
126 // Exclude printing for normal PrintGCDetails because people parse
127 // this output.
128 if (PrintGCDetails && Verbose && WizardMode) {
129 gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", total,
130 (memory_total*HeapWordSize)/1024);
131 }
132 }
133
134 // Create a new table and using alternate hash code, populate the new table
135 // with the existing strings. Set flag to use the alternate hash code afterwards.
136 void SymbolTable::rehash_table() {
137 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
138 // This should never happen with -Xshare:dump but it might in testing mode.
139 if (DumpSharedSpaces) return;
140 // Create a new symbol table
141 SymbolTable* new_table = new SymbolTable();
142
143 the_table()->move_to(new_table);
144
145 // Delete the table and buckets (entries are reused in new table).
146 delete _the_table;
147 // Don't check if we need rehashing until the table gets unbalanced again.
148 // Then rehash with a new global seed.
149 _needs_rehashing = false;
150 _the_table = new_table;
151 }
152
153 // Lookup a symbol in a bucket.
154
155 Symbol* SymbolTable::lookup(int index, const char* name,
156 int len, unsigned int hash) {
157 int count = 0;
158 for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {
159 count++; // count all entries in this bucket, not just ones with same hash
160 if (e->hash() == hash) {
161 Symbol* sym = e->literal();
162 if (sym->equals(name, len)) {
163 // something is referencing this symbol now.
164 sym->increment_refcount();
165 return sym;
166 }
167 }
168 }
169 // If the bucket size is too deep check if this hash code is insufficient.
170 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
171 _needs_rehashing = check_rehash_table(count);
172 }
173 return NULL;
174 }
175
176 // Pick hashing algorithm.
177 unsigned int SymbolTable::hash_symbol(const char* s, int len) {
178 return use_alternate_hashcode() ?
179 AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :
180 java_lang_String::hash_code(s, len);
181 }
182
183
184 // We take care not to be blocking while holding the
185 // SymbolTable_lock. Otherwise, the system might deadlock, since the
186 // symboltable is used during compilation (VM_thread) The lock free
187 // synchronization is simplified by the fact that we do not delete
188 // entries in the symbol table during normal execution (only during
189 // safepoints).
190
191 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
192 unsigned int hashValue = hash_symbol(name, len);
193 int index = the_table()->hash_to_index(hashValue);
194
195 Symbol* s = the_table()->lookup(index, name, len, hashValue);
196
197 // Found
198 if (s != NULL) return s;
199
200 // Grab SymbolTable_lock first.
201 MutexLocker ml(SymbolTable_lock, THREAD);
202
203 // Otherwise, add to symbol to table
204 return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);
205 }
206
207 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
208 char* buffer;
209 int index, len;
210 unsigned int hashValue;
211 char* name;
212 {
213 debug_only(No_Safepoint_Verifier nsv;)
214
215 name = (char*)sym->base() + begin;
216 len = end - begin;
217 hashValue = hash_symbol(name, len);
218 index = the_table()->hash_to_index(hashValue);
219 Symbol* s = the_table()->lookup(index, name, len, hashValue);
220
221 // Found
222 if (s != NULL) return s;
223 }
224
225 // Otherwise, add to symbol to table. Copy to a C string first.
226 char stack_buf[128];
227 ResourceMark rm(THREAD);
228 if (len <= 128) {
229 buffer = stack_buf;
230 } else {
231 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
232 }
233 for (int i=0; i<len; i++) {
234 buffer[i] = name[i];
235 }
236 // Make sure there is no safepoint in the code above since name can't move.
237 // We can't include the code in No_Safepoint_Verifier because of the
238 // ResourceMark.
239
240 // Grab SymbolTable_lock first.
241 MutexLocker ml(SymbolTable_lock, THREAD);
242
243 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);
244 }
245
246 Symbol* SymbolTable::lookup_only(const char* name, int len,
247 unsigned int& hash) {
248 hash = hash_symbol(name, len);
249 int index = the_table()->hash_to_index(hash);
250
251 Symbol* s = the_table()->lookup(index, name, len, hash);
252 return s;
253 }
254
255 // Look up the address of the literal in the SymbolTable for this Symbol*
256 // Do not create any new symbols
257 // Do not increment the reference count to keep this alive
258 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){
259 unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());
260 int index = the_table()->hash_to_index(hash);
261
262 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {
263 if (e->hash() == hash) {
264 Symbol* literal_sym = e->literal();
265 if (sym == literal_sym) {
266 return e->literal_addr();
267 }
268 }
269 }
270 return NULL;
271 }
272
273 // Suggestion: Push unicode-based lookup all the way into the hashing
274 // and probing logic, so there is no need for convert_to_utf8 until
275 // an actual new Symbol* is created.
276 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
277 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
278 char stack_buf[128];
279 if (utf8_length < (int) sizeof(stack_buf)) {
280 char* chars = stack_buf;
281 UNICODE::convert_to_utf8(name, utf16_length, chars);
282 return lookup(chars, utf8_length, THREAD);
283 } else {
284 ResourceMark rm(THREAD);
285 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
286 UNICODE::convert_to_utf8(name, utf16_length, chars);
287 return lookup(chars, utf8_length, THREAD);
288 }
289 }
290
291 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
292 unsigned int& hash) {
293 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
294 char stack_buf[128];
295 if (utf8_length < (int) sizeof(stack_buf)) {
296 char* chars = stack_buf;
297 UNICODE::convert_to_utf8(name, utf16_length, chars);
298 return lookup_only(chars, utf8_length, hash);
299 } else {
300 ResourceMark rm;
301 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
302 UNICODE::convert_to_utf8(name, utf16_length, chars);
303 return lookup_only(chars, utf8_length, hash);
304 }
305 }
306
307 void SymbolTable::add(ClassLoaderData* loader_data, constantPoolHandle cp,
308 int names_count,
309 const char** names, int* lengths, int* cp_indices,
310 unsigned int* hashValues, TRAPS) {
311 // Grab SymbolTable_lock first.
312 MutexLocker ml(SymbolTable_lock, THREAD);
313
314 SymbolTable* table = the_table();
315 bool added = table->basic_add(loader_data, cp, names_count, names, lengths,
316 cp_indices, hashValues, CHECK);
317 if (!added) {
318 // do it the hard way
319 for (int i=0; i<names_count; i++) {
320 int index = table->hash_to_index(hashValues[i]);
321 bool c_heap = !loader_data->is_the_null_class_loader_data();
322 Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);
323 cp->symbol_at_put(cp_indices[i], sym);
324 }
325 }
326 }
327
328 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
329 unsigned int hash;
330 Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);
331 if (result != NULL) {
332 return result;
333 }
334 // Grab SymbolTable_lock first.
335 MutexLocker ml(SymbolTable_lock, THREAD);
336
337 SymbolTable* table = the_table();
338 int index = table->hash_to_index(hash);
339 return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);
340 }
341
342 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,
343 unsigned int hashValue_arg, bool c_heap, TRAPS) {
344 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
345 "proposed name of symbol must be stable");
346
347 // Don't allow symbols to be created which cannot fit in a Symbol*.
348 if (len > Symbol::max_length()) {
349 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
350 "name is too long to represent");
351 }
352
353 // Cannot hit a safepoint in this function because the "this" pointer can move.
354 No_Safepoint_Verifier nsv;
355
356 // Check if the symbol table has been rehashed, if so, need to recalculate
357 // the hash value and index.
358 unsigned int hashValue;
359 int index;
360 if (use_alternate_hashcode()) {
361 hashValue = hash_symbol((const char*)name, len);
362 index = hash_to_index(hashValue);
363 } else {
364 hashValue = hashValue_arg;
365 index = index_arg;
366 }
367
368 // Since look-up was done lock-free, we need to check if another
369 // thread beat us in the race to insert the symbol.
370 Symbol* test = lookup(index, (char*)name, len, hashValue);
371 if (test != NULL) {
372 // A race occurred and another thread introduced the symbol.
373 assert(test->refcount() != 0, "lookup should have incremented the count");
374 return test;
375 }
376
377 // Create a new symbol.
378 Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);
379 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
380
381 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
382 add_entry(index, entry);
383 return sym;
384 }
385
386 // This version of basic_add adds symbols in batch from the constant pool
387 // parsing.
388 bool SymbolTable::basic_add(ClassLoaderData* loader_data, constantPoolHandle cp,
389 int names_count,
390 const char** names, int* lengths,
391 int* cp_indices, unsigned int* hashValues,
392 TRAPS) {
393
394 // Check symbol names are not too long. If any are too long, don't add any.
395 for (int i = 0; i< names_count; i++) {
396 if (lengths[i] > Symbol::max_length()) {
397 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
398 "name is too long to represent");
399 }
400 }
401
402 // Cannot hit a safepoint in this function because the "this" pointer can move.
403 No_Safepoint_Verifier nsv;
404
405 for (int i=0; i<names_count; i++) {
406 // Check if the symbol table has been rehashed, if so, need to recalculate
407 // the hash value.
408 unsigned int hashValue;
409 if (use_alternate_hashcode()) {
410 hashValue = hash_symbol(names[i], lengths[i]);
411 } else {
412 hashValue = hashValues[i];
413 }
414 // Since look-up was done lock-free, we need to check if another
415 // thread beat us in the race to insert the symbol.
416 int index = hash_to_index(hashValue);
417 Symbol* test = lookup(index, names[i], lengths[i], hashValue);
418 if (test != NULL) {
419 // A race occurred and another thread introduced the symbol, this one
420 // will be dropped and collected. Use test instead.
421 cp->symbol_at_put(cp_indices[i], test);
422 assert(test->refcount() != 0, "lookup should have incremented the count");
423 } else {
424 // Create a new symbol. The null class loader is never unloaded so these
425 // are allocated specially in a permanent arena.
426 bool c_heap = !loader_data->is_the_null_class_loader_data();
427 Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));
428 assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized"); // why wouldn't it be???
429 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
430 add_entry(index, entry);
431 cp->symbol_at_put(cp_indices[i], sym);
432 }
433 }
434 return true;
435 }
436
437
438 void SymbolTable::verify() {
439 for (int i = 0; i < the_table()->table_size(); ++i) {
440 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
441 for ( ; p != NULL; p = p->next()) {
442 Symbol* s = (Symbol*)(p->literal());
443 guarantee(s != NULL, "symbol is NULL");
444 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
445 guarantee(p->hash() == h, "broken hash in symbol table entry");
446 guarantee(the_table()->hash_to_index(h) == i,
447 "wrong index in symbol table");
448 }
449 }
450 }
451
452 void SymbolTable::dump(outputStream* st) {
453 the_table()->dump_table(st, "SymbolTable");
454 }
455
456
457 //---------------------------------------------------------------------------
458 // Non-product code
459
460 #ifndef PRODUCT
461
462 void SymbolTable::print_histogram() {
463 MutexLocker ml(SymbolTable_lock);
464 const int results_length = 100;
465 int results[results_length];
466 int i,j;
467
468 // initialize results to zero
469 for (j = 0; j < results_length; j++) {
470 results[j] = 0;
471 }
472
473 int total = 0;
474 int max_symbols = 0;
475 int out_of_range = 0;
476 int memory_total = 0;
477 int count = 0;
478 for (i = 0; i < the_table()->table_size(); i++) {
479 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
480 for ( ; p != NULL; p = p->next()) {
481 memory_total += p->literal()->size();
482 count++;
483 int counter = p->literal()->utf8_length();
484 total += counter;
485 if (counter < results_length) {
486 results[counter]++;
487 } else {
488 out_of_range++;
489 }
490 max_symbols = MAX2(max_symbols, counter);
491 }
492 }
493 tty->print_cr("Symbol Table:");
494 tty->print_cr("Total number of symbols %5d", count);
495 tty->print_cr("Total size in memory %5dK",
496 (memory_total*HeapWordSize)/1024);
497 tty->print_cr("Total counted %5d", symbols_counted);
498 tty->print_cr("Total removed %5d", symbols_removed);
499 if (symbols_counted > 0) {
500 tty->print_cr("Percent removed %3.2f",
501 ((float)symbols_removed/(float)symbols_counted)* 100);
502 }
503 tty->print_cr("Reference counts %5d", Symbol::_total_count);
504 tty->print_cr("Symbol arena size %5d used %5d",
505 arena()->size_in_bytes(), arena()->used());
506 tty->print_cr("Histogram of symbol length:");
507 tty->print_cr("%8s %5d", "Total ", total);
508 tty->print_cr("%8s %5d", "Maximum", max_symbols);
509 tty->print_cr("%8s %3.2f", "Average",
510 ((float) total / (float) the_table()->table_size()));
511 tty->print_cr("%s", "Histogram:");
512 tty->print_cr(" %s %29s", "Length", "Number chains that length");
513 for (i = 0; i < results_length; i++) {
514 if (results[i] > 0) {
515 tty->print_cr("%6d %10d", i, results[i]);
516 }
517 }
518 if (Verbose) {
519 int line_length = 70;
520 tty->print_cr("%s %30s", " Length", "Number chains that length");
521 for (i = 0; i < results_length; i++) {
522 if (results[i] > 0) {
523 tty->print("%4d", i);
524 for (j = 0; (j < results[i]) && (j < line_length); j++) {
525 tty->print("%1s", "*");
526 }
527 if (j == line_length) {
528 tty->print("%1s", "+");
529 }
530 tty->cr();
531 }
532 }
533 }
534 tty->print_cr(" %s %d: %d\n", "Number chains longer than",
535 results_length, out_of_range);
536 }
537
538 void SymbolTable::print() {
539 for (int i = 0; i < the_table()->table_size(); ++i) {
540 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
541 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
542 if (entry != NULL) {
543 while (entry != NULL) {
544 tty->print(PTR_FORMAT " ", entry->literal());
545 entry->literal()->print();
546 tty->print(" %d", entry->literal()->refcount());
547 p = entry->next_addr();
548 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
549 }
550 tty->cr();
551 }
552 }
553 }
554 #endif // PRODUCT
555
556 // --------------------------------------------------------------------------
557
558 #ifdef ASSERT
559 class StableMemoryChecker : public StackObj {
560 enum { _bufsize = wordSize*4 };
561
562 address _region;
563 jint _size;
564 u1 _save_buf[_bufsize];
565
566 int sample(u1* save_buf) {
567 if (_size <= _bufsize) {
568 memcpy(save_buf, _region, _size);
569 return _size;
570 } else {
571 // copy head and tail
572 memcpy(&save_buf[0], _region, _bufsize/2);
573 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
574 return (_bufsize/2)*2;
575 }
576 }
577
578 public:
579 StableMemoryChecker(const void* region, jint size) {
580 _region = (address) region;
581 _size = size;
582 sample(_save_buf);
583 }
584
585 bool verify() {
586 u1 check_buf[sizeof(_save_buf)];
587 int check_size = sample(check_buf);
588 return (0 == memcmp(_save_buf, check_buf, check_size));
589 }
590
591 void set_region(const void* region) { _region = (address) region; }
592 };
593 #endif
594
595
596 // --------------------------------------------------------------------------
597 StringTable* StringTable::_the_table = NULL;
598
599 bool StringTable::_needs_rehashing = false;
600
601 // Pick hashing algorithm
602 unsigned int StringTable::hash_string(const jchar* s, int len) {
603 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
604 java_lang_String::hash_code(s, len);
605 }
606
607 oop StringTable::lookup(int index, jchar* name,
608 int len, unsigned int hash) {
609 int count = 0;
610 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
611 count++;
612 if (l->hash() == hash) {
613 if (java_lang_String::equals(l->literal(), name, len)) {
614 return l->literal();
615 }
616 }
617 }
618 // If the bucket size is too deep check if this hash code is insufficient.
619 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
620 _needs_rehashing = check_rehash_table(count);
621 }
622 return NULL;
623 }
624
625
626 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
627 int len, unsigned int hashValue_arg, TRAPS) {
628
629 assert(java_lang_String::equals(string(), name, len),
630 "string must be properly initialized");
631 // Cannot hit a safepoint in this function because the "this" pointer can move.
632 No_Safepoint_Verifier nsv;
633
634 // Check if the symbol table has been rehashed, if so, need to recalculate
635 // the hash value and index before second lookup.
636 unsigned int hashValue;
637 int index;
638 if (use_alternate_hashcode()) {
639 hashValue = hash_string(name, len);
640 index = hash_to_index(hashValue);
641 } else {
642 hashValue = hashValue_arg;
643 index = index_arg;
644 }
645
646 // Since look-up was done lock-free, we need to check if another
647 // thread beat us in the race to insert the symbol.
648
649 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
650 if (test != NULL) {
651 // Entry already added
652 return test;
653 }
654
655 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
656 add_entry(index, entry);
657 return string();
658 }
659
660
661 oop StringTable::lookup(Symbol* symbol) {
662 ResourceMark rm;
663 int length;
664 jchar* chars = symbol->as_unicode(length);
665 return lookup(chars, length);
666 }
667
668
669 oop StringTable::lookup(jchar* name, int len) {
670 unsigned int hash = hash_string(name, len);
671 int index = the_table()->hash_to_index(hash);
672 return the_table()->lookup(index, name, len, hash);
673 }
674
675
676 oop StringTable::intern(Handle string_or_null, jchar* name,
677 int len, TRAPS) {
678 unsigned int hashValue = hash_string(name, len);
679 int index = the_table()->hash_to_index(hashValue);
680 oop found_string = the_table()->lookup(index, name, len, hashValue);
681
682 // Found
683 if (found_string != NULL) return found_string;
684
685 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
686 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
687 "proposed name of symbol must be stable");
688
689 Handle string;
690 // try to reuse the string if possible
691 if (!string_or_null.is_null()) {
692 string = string_or_null;
693 } else {
694 string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
695 }
696
697 // Grab the StringTable_lock before getting the_table() because it could
698 // change at safepoint.
699 MutexLocker ml(StringTable_lock, THREAD);
700
701 // Otherwise, add to symbol to table
702 return the_table()->basic_add(index, string, name, len,
703 hashValue, CHECK_NULL);
704 }
705
706 oop StringTable::intern(Symbol* symbol, TRAPS) {
707 if (symbol == NULL) return NULL;
708 ResourceMark rm(THREAD);
709 int length;
710 jchar* chars = symbol->as_unicode(length);
711 Handle string;
712 oop result = intern(string, chars, length, CHECK_NULL);
713 return result;
714 }
715
716
717 oop StringTable::intern(oop string, TRAPS)
718 {
719 if (string == NULL) return NULL;
720 ResourceMark rm(THREAD);
721 int length;
722 Handle h_string (THREAD, string);
723 jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
724 oop result = intern(h_string, chars, length, CHECK_NULL);
725 return result;
726 }
727
728
729 oop StringTable::intern(const char* utf8_string, TRAPS) {
730 if (utf8_string == NULL) return NULL;
731 ResourceMark rm(THREAD);
732 int length = UTF8::unicode_length(utf8_string);
733 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
734 UTF8::convert_to_unicode(utf8_string, chars, length);
735 Handle string;
736 oop result = intern(string, chars, length, CHECK_NULL);
737 return result;
738 }
739
740 void StringTable::unlink(BoolObjectClosure* is_alive) {
741 // Readers of the table are unlocked, so we should only be removing
742 // entries at a safepoint.
743 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
744 for (int i = 0; i < the_table()->table_size(); ++i) {
745 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
746 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
747 while (entry != NULL) {
748 assert(entry->literal() != NULL, "just checking");
749 assert(!entry->is_shared(), "CDS not used for the StringTable");
750
751 if (is_alive->do_object_b(entry->literal())) {
752 p = entry->next_addr();
753 } else {
754 *p = entry->next();
755 the_table()->free_entry(entry);
756 }
757 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
758 }
759 }
760 }
761
762 void StringTable::oops_do(OopClosure* f) {
763 for (int i = 0; i < the_table()->table_size(); ++i) {
764 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
765 while (entry != NULL) {
766 assert(entry->literal() != NULL, "just checking");
767 assert(!entry->is_shared(), "CDS not used for the StringTable");
768
769 f->do_oop((oop*)entry->literal_addr());
770
771 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(entry->next());
772 }
773 }
774 }
775
776 void StringTable::verify() {
777 for (int i = 0; i < the_table()->table_size(); ++i) {
778 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
779 for ( ; p != NULL; p = p->next()) {
780 oop s = p->literal();
781 guarantee(s != NULL, "interned string is NULL");
782 unsigned int h = java_lang_String::hash_string(s);
783 guarantee(p->hash() == h, "broken hash in string table entry");
784 guarantee(the_table()->hash_to_index(h) == i,
785 "wrong index in string table");
786 }
787 }
788 }
789
790 void StringTable::dump(outputStream* st) {
791 the_table()->dump_table(st, "StringTable");
792 }
793
794
795 // Create a new table and using alternate hash code, populate the new table
796 // with the existing strings. Set flag to use the alternate hash code afterwards.
797 void StringTable::rehash_table() {
798 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
799 // This should never happen with -Xshare:dump but it might in testing mode.
800 if (DumpSharedSpaces) return;
801 StringTable* new_table = new StringTable();
802
803 // Rehash the table
804 the_table()->move_to(new_table);
805
806 // Delete the table and buckets (entries are reused in new table).
807 delete _the_table;
808 // Don't check if we need rehashing until the table gets unbalanced again.
809 // Then rehash with a new global seed.
810 _needs_rehashing = false;
811 _the_table = new_table;
812 }