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