Thu, 11 Apr 2013 09:08:15 -0700
8011972: Field can be erroneously marked as contended when @Contended annotation isn't present
Reviewed-by: kvn, kmo, shade
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.
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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
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23 */
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"
40 // --------------------------------------------------------------------------
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;
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");
50 Symbol* sym;
52 if (DumpSharedSpaces) {
53 // Allocate all symbols to CLD shared metaspace
54 sym = new (len, ClassLoaderData::the_null_class_loader_data(), THREAD) Symbol(name, len, -1);
55 } else if (c_heap) {
56 // refcount starts as 1
57 sym = new (len, THREAD) Symbol(name, len, 1);
58 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
59 } else {
60 // Allocate to global arena
61 sym = new (len, arena(), THREAD) Symbol(name, len, -1);
62 }
63 return sym;
64 }
66 void SymbolTable::initialize_symbols(int arena_alloc_size) {
67 // Initialize the arena for global symbols, size passed in depends on CDS.
68 if (arena_alloc_size == 0) {
69 _arena = new (mtSymbol) Arena();
70 } else {
71 _arena = new (mtSymbol) Arena(arena_alloc_size);
72 }
73 }
75 // Call function for all symbols in the symbol table.
76 void SymbolTable::symbols_do(SymbolClosure *cl) {
77 const int n = the_table()->table_size();
78 for (int i = 0; i < n; i++) {
79 for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
80 p != NULL;
81 p = p->next()) {
82 cl->do_symbol(p->literal_addr());
83 }
84 }
85 }
87 int SymbolTable::symbols_removed = 0;
88 int SymbolTable::symbols_counted = 0;
90 // Remove unreferenced symbols from the symbol table
91 // This is done late during GC.
92 void SymbolTable::unlink() {
93 int removed = 0;
94 int total = 0;
95 size_t memory_total = 0;
96 for (int i = 0; i < the_table()->table_size(); ++i) {
97 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
98 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
99 while (entry != NULL) {
100 // Shared entries are normally at the end of the bucket and if we run into
101 // a shared entry, then there is nothing more to remove. However, if we
102 // have rehashed the table, then the shared entries are no longer at the
103 // end of the bucket.
104 if (entry->is_shared() && !use_alternate_hashcode()) {
105 break;
106 }
107 Symbol* s = entry->literal();
108 memory_total += s->size();
109 total++;
110 assert(s != NULL, "just checking");
111 // If reference count is zero, remove.
112 if (s->refcount() == 0) {
113 assert(!entry->is_shared(), "shared entries should be kept live");
114 delete s;
115 removed++;
116 *p = entry->next();
117 the_table()->free_entry(entry);
118 } else {
119 p = entry->next_addr();
120 }
121 // get next entry
122 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
123 }
124 }
125 symbols_removed += removed;
126 symbols_counted += total;
127 // Exclude printing for normal PrintGCDetails because people parse
128 // this output.
129 if (PrintGCDetails && Verbose && WizardMode) {
130 gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", total,
131 (memory_total*HeapWordSize)/1024);
132 }
133 }
135 // Create a new table and using alternate hash code, populate the new table
136 // with the existing strings. Set flag to use the alternate hash code afterwards.
137 void SymbolTable::rehash_table() {
138 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
139 // This should never happen with -Xshare:dump but it might in testing mode.
140 if (DumpSharedSpaces) return;
141 // Create a new symbol table
142 SymbolTable* new_table = new SymbolTable();
144 the_table()->move_to(new_table);
146 // Delete the table and buckets (entries are reused in new table).
147 delete _the_table;
148 // Don't check if we need rehashing until the table gets unbalanced again.
149 // Then rehash with a new global seed.
150 _needs_rehashing = false;
151 _the_table = new_table;
152 }
154 // Lookup a symbol in a bucket.
156 Symbol* SymbolTable::lookup(int index, const char* name,
157 int len, unsigned int hash) {
158 int count = 0;
159 for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {
160 count++; // count all entries in this bucket, not just ones with same hash
161 if (e->hash() == hash) {
162 Symbol* sym = e->literal();
163 if (sym->equals(name, len)) {
164 // something is referencing this symbol now.
165 sym->increment_refcount();
166 return sym;
167 }
168 }
169 }
170 // If the bucket size is too deep check if this hash code is insufficient.
171 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
172 _needs_rehashing = check_rehash_table(count);
173 }
174 return NULL;
175 }
177 // Pick hashing algorithm.
178 unsigned int SymbolTable::hash_symbol(const char* s, int len) {
179 return use_alternate_hashcode() ?
180 AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :
181 java_lang_String::hash_code(s, len);
182 }
185 // We take care not to be blocking while holding the
186 // SymbolTable_lock. Otherwise, the system might deadlock, since the
187 // symboltable is used during compilation (VM_thread) The lock free
188 // synchronization is simplified by the fact that we do not delete
189 // entries in the symbol table during normal execution (only during
190 // safepoints).
192 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
193 unsigned int hashValue = hash_symbol(name, len);
194 int index = the_table()->hash_to_index(hashValue);
196 Symbol* s = the_table()->lookup(index, name, len, hashValue);
198 // Found
199 if (s != NULL) return s;
201 // Grab SymbolTable_lock first.
202 MutexLocker ml(SymbolTable_lock, THREAD);
204 // Otherwise, add to symbol to table
205 return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);
206 }
208 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
209 char* buffer;
210 int index, len;
211 unsigned int hashValue;
212 char* name;
213 {
214 debug_only(No_Safepoint_Verifier nsv;)
216 name = (char*)sym->base() + begin;
217 len = end - begin;
218 hashValue = hash_symbol(name, len);
219 index = the_table()->hash_to_index(hashValue);
220 Symbol* s = the_table()->lookup(index, name, len, hashValue);
222 // Found
223 if (s != NULL) return s;
224 }
226 // Otherwise, add to symbol to table. Copy to a C string first.
227 char stack_buf[128];
228 ResourceMark rm(THREAD);
229 if (len <= 128) {
230 buffer = stack_buf;
231 } else {
232 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
233 }
234 for (int i=0; i<len; i++) {
235 buffer[i] = name[i];
236 }
237 // Make sure there is no safepoint in the code above since name can't move.
238 // We can't include the code in No_Safepoint_Verifier because of the
239 // ResourceMark.
241 // Grab SymbolTable_lock first.
242 MutexLocker ml(SymbolTable_lock, THREAD);
244 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);
245 }
247 Symbol* SymbolTable::lookup_only(const char* name, int len,
248 unsigned int& hash) {
249 hash = hash_symbol(name, len);
250 int index = the_table()->hash_to_index(hash);
252 Symbol* s = the_table()->lookup(index, name, len, hash);
253 return s;
254 }
256 // Look up the address of the literal in the SymbolTable for this Symbol*
257 // Do not create any new symbols
258 // Do not increment the reference count to keep this alive
259 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){
260 unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());
261 int index = the_table()->hash_to_index(hash);
263 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {
264 if (e->hash() == hash) {
265 Symbol* literal_sym = e->literal();
266 if (sym == literal_sym) {
267 return e->literal_addr();
268 }
269 }
270 }
271 return NULL;
272 }
274 // Suggestion: Push unicode-based lookup all the way into the hashing
275 // and probing logic, so there is no need for convert_to_utf8 until
276 // an actual new Symbol* is created.
277 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
278 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
279 char stack_buf[128];
280 if (utf8_length < (int) sizeof(stack_buf)) {
281 char* chars = stack_buf;
282 UNICODE::convert_to_utf8(name, utf16_length, chars);
283 return lookup(chars, utf8_length, THREAD);
284 } else {
285 ResourceMark rm(THREAD);
286 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
287 UNICODE::convert_to_utf8(name, utf16_length, chars);
288 return lookup(chars, utf8_length, THREAD);
289 }
290 }
292 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
293 unsigned int& hash) {
294 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
295 char stack_buf[128];
296 if (utf8_length < (int) sizeof(stack_buf)) {
297 char* chars = stack_buf;
298 UNICODE::convert_to_utf8(name, utf16_length, chars);
299 return lookup_only(chars, utf8_length, hash);
300 } else {
301 ResourceMark rm;
302 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
303 UNICODE::convert_to_utf8(name, utf16_length, chars);
304 return lookup_only(chars, utf8_length, hash);
305 }
306 }
308 void SymbolTable::add(ClassLoaderData* loader_data, constantPoolHandle cp,
309 int names_count,
310 const char** names, int* lengths, int* cp_indices,
311 unsigned int* hashValues, TRAPS) {
312 // Grab SymbolTable_lock first.
313 MutexLocker ml(SymbolTable_lock, THREAD);
315 SymbolTable* table = the_table();
316 bool added = table->basic_add(loader_data, cp, names_count, names, lengths,
317 cp_indices, hashValues, CHECK);
318 if (!added) {
319 // do it the hard way
320 for (int i=0; i<names_count; i++) {
321 int index = table->hash_to_index(hashValues[i]);
322 bool c_heap = !loader_data->is_the_null_class_loader_data();
323 Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);
324 cp->symbol_at_put(cp_indices[i], sym);
325 }
326 }
327 }
329 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
330 unsigned int hash;
331 Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);
332 if (result != NULL) {
333 return result;
334 }
335 // Grab SymbolTable_lock first.
336 MutexLocker ml(SymbolTable_lock, THREAD);
338 SymbolTable* table = the_table();
339 int index = table->hash_to_index(hash);
340 return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);
341 }
343 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,
344 unsigned int hashValue_arg, bool c_heap, TRAPS) {
345 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
346 "proposed name of symbol must be stable");
348 // Don't allow symbols to be created which cannot fit in a Symbol*.
349 if (len > Symbol::max_length()) {
350 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
351 "name is too long to represent");
352 }
354 // Cannot hit a safepoint in this function because the "this" pointer can move.
355 No_Safepoint_Verifier nsv;
357 // Check if the symbol table has been rehashed, if so, need to recalculate
358 // the hash value and index.
359 unsigned int hashValue;
360 int index;
361 if (use_alternate_hashcode()) {
362 hashValue = hash_symbol((const char*)name, len);
363 index = hash_to_index(hashValue);
364 } else {
365 hashValue = hashValue_arg;
366 index = index_arg;
367 }
369 // Since look-up was done lock-free, we need to check if another
370 // thread beat us in the race to insert the symbol.
371 Symbol* test = lookup(index, (char*)name, len, hashValue);
372 if (test != NULL) {
373 // A race occurred and another thread introduced the symbol.
374 assert(test->refcount() != 0, "lookup should have incremented the count");
375 return test;
376 }
378 // Create a new symbol.
379 Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);
380 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
382 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
383 add_entry(index, entry);
384 return sym;
385 }
387 // This version of basic_add adds symbols in batch from the constant pool
388 // parsing.
389 bool SymbolTable::basic_add(ClassLoaderData* loader_data, constantPoolHandle cp,
390 int names_count,
391 const char** names, int* lengths,
392 int* cp_indices, unsigned int* hashValues,
393 TRAPS) {
395 // Check symbol names are not too long. If any are too long, don't add any.
396 for (int i = 0; i< names_count; i++) {
397 if (lengths[i] > Symbol::max_length()) {
398 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
399 "name is too long to represent");
400 }
401 }
403 // Cannot hit a safepoint in this function because the "this" pointer can move.
404 No_Safepoint_Verifier nsv;
406 for (int i=0; i<names_count; i++) {
407 // Check if the symbol table has been rehashed, if so, need to recalculate
408 // the hash value.
409 unsigned int hashValue;
410 if (use_alternate_hashcode()) {
411 hashValue = hash_symbol(names[i], lengths[i]);
412 } else {
413 hashValue = hashValues[i];
414 }
415 // Since look-up was done lock-free, we need to check if another
416 // thread beat us in the race to insert the symbol.
417 int index = hash_to_index(hashValue);
418 Symbol* test = lookup(index, names[i], lengths[i], hashValue);
419 if (test != NULL) {
420 // A race occurred and another thread introduced the symbol, this one
421 // will be dropped and collected. Use test instead.
422 cp->symbol_at_put(cp_indices[i], test);
423 assert(test->refcount() != 0, "lookup should have incremented the count");
424 } else {
425 // Create a new symbol. The null class loader is never unloaded so these
426 // are allocated specially in a permanent arena.
427 bool c_heap = !loader_data->is_the_null_class_loader_data();
428 Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));
429 assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized"); // why wouldn't it be???
430 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
431 add_entry(index, entry);
432 cp->symbol_at_put(cp_indices[i], sym);
433 }
434 }
435 return true;
436 }
439 void SymbolTable::verify() {
440 for (int i = 0; i < the_table()->table_size(); ++i) {
441 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
442 for ( ; p != NULL; p = p->next()) {
443 Symbol* s = (Symbol*)(p->literal());
444 guarantee(s != NULL, "symbol is NULL");
445 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
446 guarantee(p->hash() == h, "broken hash in symbol table entry");
447 guarantee(the_table()->hash_to_index(h) == i,
448 "wrong index in symbol table");
449 }
450 }
451 }
453 void SymbolTable::dump(outputStream* st) {
454 NumberSeq summary;
455 for (int i = 0; i < the_table()->table_size(); ++i) {
456 int count = 0;
457 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(i);
458 e != NULL; e = e->next()) {
459 count++;
460 }
461 summary.add((double)count);
462 }
463 st->print_cr("SymbolTable statistics:");
464 st->print_cr("Number of buckets : %7d", summary.num());
465 st->print_cr("Average bucket size : %7.0f", summary.avg());
466 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
467 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
468 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
469 }
472 //---------------------------------------------------------------------------
473 // Non-product code
475 #ifndef PRODUCT
477 void SymbolTable::print_histogram() {
478 MutexLocker ml(SymbolTable_lock);
479 const int results_length = 100;
480 int results[results_length];
481 int i,j;
483 // initialize results to zero
484 for (j = 0; j < results_length; j++) {
485 results[j] = 0;
486 }
488 int total = 0;
489 int max_symbols = 0;
490 int out_of_range = 0;
491 int memory_total = 0;
492 int count = 0;
493 for (i = 0; i < the_table()->table_size(); i++) {
494 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
495 for ( ; p != NULL; p = p->next()) {
496 memory_total += p->literal()->size();
497 count++;
498 int counter = p->literal()->utf8_length();
499 total += counter;
500 if (counter < results_length) {
501 results[counter]++;
502 } else {
503 out_of_range++;
504 }
505 max_symbols = MAX2(max_symbols, counter);
506 }
507 }
508 tty->print_cr("Symbol Table:");
509 tty->print_cr("Total number of symbols %5d", count);
510 tty->print_cr("Total size in memory %5dK",
511 (memory_total*HeapWordSize)/1024);
512 tty->print_cr("Total counted %5d", symbols_counted);
513 tty->print_cr("Total removed %5d", symbols_removed);
514 if (symbols_counted > 0) {
515 tty->print_cr("Percent removed %3.2f",
516 ((float)symbols_removed/(float)symbols_counted)* 100);
517 }
518 tty->print_cr("Reference counts %5d", Symbol::_total_count);
519 tty->print_cr("Symbol arena size %5d used %5d",
520 arena()->size_in_bytes(), arena()->used());
521 tty->print_cr("Histogram of symbol length:");
522 tty->print_cr("%8s %5d", "Total ", total);
523 tty->print_cr("%8s %5d", "Maximum", max_symbols);
524 tty->print_cr("%8s %3.2f", "Average",
525 ((float) total / (float) the_table()->table_size()));
526 tty->print_cr("%s", "Histogram:");
527 tty->print_cr(" %s %29s", "Length", "Number chains that length");
528 for (i = 0; i < results_length; i++) {
529 if (results[i] > 0) {
530 tty->print_cr("%6d %10d", i, results[i]);
531 }
532 }
533 if (Verbose) {
534 int line_length = 70;
535 tty->print_cr("%s %30s", " Length", "Number chains that length");
536 for (i = 0; i < results_length; i++) {
537 if (results[i] > 0) {
538 tty->print("%4d", i);
539 for (j = 0; (j < results[i]) && (j < line_length); j++) {
540 tty->print("%1s", "*");
541 }
542 if (j == line_length) {
543 tty->print("%1s", "+");
544 }
545 tty->cr();
546 }
547 }
548 }
549 tty->print_cr(" %s %d: %d\n", "Number chains longer than",
550 results_length, out_of_range);
551 }
553 void SymbolTable::print() {
554 for (int i = 0; i < the_table()->table_size(); ++i) {
555 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
556 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
557 if (entry != NULL) {
558 while (entry != NULL) {
559 tty->print(PTR_FORMAT " ", entry->literal());
560 entry->literal()->print();
561 tty->print(" %d", entry->literal()->refcount());
562 p = entry->next_addr();
563 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
564 }
565 tty->cr();
566 }
567 }
568 }
569 #endif // PRODUCT
571 // --------------------------------------------------------------------------
573 #ifdef ASSERT
574 class StableMemoryChecker : public StackObj {
575 enum { _bufsize = wordSize*4 };
577 address _region;
578 jint _size;
579 u1 _save_buf[_bufsize];
581 int sample(u1* save_buf) {
582 if (_size <= _bufsize) {
583 memcpy(save_buf, _region, _size);
584 return _size;
585 } else {
586 // copy head and tail
587 memcpy(&save_buf[0], _region, _bufsize/2);
588 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
589 return (_bufsize/2)*2;
590 }
591 }
593 public:
594 StableMemoryChecker(const void* region, jint size) {
595 _region = (address) region;
596 _size = size;
597 sample(_save_buf);
598 }
600 bool verify() {
601 u1 check_buf[sizeof(_save_buf)];
602 int check_size = sample(check_buf);
603 return (0 == memcmp(_save_buf, check_buf, check_size));
604 }
606 void set_region(const void* region) { _region = (address) region; }
607 };
608 #endif
611 // --------------------------------------------------------------------------
612 StringTable* StringTable::_the_table = NULL;
614 bool StringTable::_needs_rehashing = false;
616 // Pick hashing algorithm
617 unsigned int StringTable::hash_string(const jchar* s, int len) {
618 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
619 java_lang_String::hash_code(s, len);
620 }
622 oop StringTable::lookup(int index, jchar* name,
623 int len, unsigned int hash) {
624 int count = 0;
625 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
626 count++;
627 if (l->hash() == hash) {
628 if (java_lang_String::equals(l->literal(), name, len)) {
629 return l->literal();
630 }
631 }
632 }
633 // If the bucket size is too deep check if this hash code is insufficient.
634 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
635 _needs_rehashing = check_rehash_table(count);
636 }
637 return NULL;
638 }
641 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
642 int len, unsigned int hashValue_arg, TRAPS) {
644 assert(java_lang_String::equals(string(), name, len),
645 "string must be properly initialized");
646 // Cannot hit a safepoint in this function because the "this" pointer can move.
647 No_Safepoint_Verifier nsv;
649 // Check if the symbol table has been rehashed, if so, need to recalculate
650 // the hash value and index before second lookup.
651 unsigned int hashValue;
652 int index;
653 if (use_alternate_hashcode()) {
654 hashValue = hash_string(name, len);
655 index = hash_to_index(hashValue);
656 } else {
657 hashValue = hashValue_arg;
658 index = index_arg;
659 }
661 // Since look-up was done lock-free, we need to check if another
662 // thread beat us in the race to insert the symbol.
664 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
665 if (test != NULL) {
666 // Entry already added
667 return test;
668 }
670 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
671 add_entry(index, entry);
672 return string();
673 }
676 oop StringTable::lookup(Symbol* symbol) {
677 ResourceMark rm;
678 int length;
679 jchar* chars = symbol->as_unicode(length);
680 return lookup(chars, length);
681 }
684 oop StringTable::lookup(jchar* name, int len) {
685 unsigned int hash = hash_string(name, len);
686 int index = the_table()->hash_to_index(hash);
687 return the_table()->lookup(index, name, len, hash);
688 }
691 oop StringTable::intern(Handle string_or_null, jchar* name,
692 int len, TRAPS) {
693 unsigned int hashValue = hash_string(name, len);
694 int index = the_table()->hash_to_index(hashValue);
695 oop found_string = the_table()->lookup(index, name, len, hashValue);
697 // Found
698 if (found_string != NULL) return found_string;
700 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
701 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
702 "proposed name of symbol must be stable");
704 Handle string;
705 // try to reuse the string if possible
706 if (!string_or_null.is_null()) {
707 string = string_or_null;
708 } else {
709 string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
710 }
712 // Grab the StringTable_lock before getting the_table() because it could
713 // change at safepoint.
714 MutexLocker ml(StringTable_lock, THREAD);
716 // Otherwise, add to symbol to table
717 return the_table()->basic_add(index, string, name, len,
718 hashValue, CHECK_NULL);
719 }
721 oop StringTable::intern(Symbol* symbol, TRAPS) {
722 if (symbol == NULL) return NULL;
723 ResourceMark rm(THREAD);
724 int length;
725 jchar* chars = symbol->as_unicode(length);
726 Handle string;
727 oop result = intern(string, chars, length, CHECK_NULL);
728 return result;
729 }
732 oop StringTable::intern(oop string, TRAPS)
733 {
734 if (string == NULL) return NULL;
735 ResourceMark rm(THREAD);
736 int length;
737 Handle h_string (THREAD, string);
738 jchar* chars = java_lang_String::as_unicode_string(string, length);
739 oop result = intern(h_string, chars, length, CHECK_NULL);
740 return result;
741 }
744 oop StringTable::intern(const char* utf8_string, TRAPS) {
745 if (utf8_string == NULL) return NULL;
746 ResourceMark rm(THREAD);
747 int length = UTF8::unicode_length(utf8_string);
748 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
749 UTF8::convert_to_unicode(utf8_string, chars, length);
750 Handle string;
751 oop result = intern(string, chars, length, CHECK_NULL);
752 return result;
753 }
755 void StringTable::unlink(BoolObjectClosure* is_alive) {
756 // Readers of the table are unlocked, so we should only be removing
757 // entries at a safepoint.
758 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
759 for (int i = 0; i < the_table()->table_size(); ++i) {
760 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
761 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
762 while (entry != NULL) {
763 // Shared entries are normally at the end of the bucket and if we run into
764 // a shared entry, then there is nothing more to remove. However, if we
765 // have rehashed the table, then the shared entries are no longer at the
766 // end of the bucket.
767 if (entry->is_shared() && !use_alternate_hashcode()) {
768 break;
769 }
770 assert(entry->literal() != NULL, "just checking");
771 if (entry->is_shared() || is_alive->do_object_b(entry->literal())) {
772 p = entry->next_addr();
773 } else {
774 *p = entry->next();
775 the_table()->free_entry(entry);
776 }
777 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
778 }
779 }
780 }
782 void StringTable::oops_do(OopClosure* f) {
783 for (int i = 0; i < the_table()->table_size(); ++i) {
784 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
785 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
786 while (entry != NULL) {
787 f->do_oop((oop*)entry->literal_addr());
789 // Did the closure remove the literal from the table?
790 if (entry->literal() == NULL) {
791 assert(!entry->is_shared(), "immutable hashtable entry?");
792 *p = entry->next();
793 the_table()->free_entry(entry);
794 } else {
795 p = entry->next_addr();
796 }
797 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
798 }
799 }
800 }
802 void StringTable::verify() {
803 for (int i = 0; i < the_table()->table_size(); ++i) {
804 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
805 for ( ; p != NULL; p = p->next()) {
806 oop s = p->literal();
807 guarantee(s != NULL, "interned string is NULL");
808 unsigned int h = java_lang_String::hash_string(s);
809 guarantee(p->hash() == h, "broken hash in string table entry");
810 guarantee(the_table()->hash_to_index(h) == i,
811 "wrong index in string table");
812 }
813 }
814 }
816 void StringTable::dump(outputStream* st) {
817 NumberSeq summary;
818 for (int i = 0; i < the_table()->table_size(); ++i) {
819 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
820 int count = 0;
821 for ( ; p != NULL; p = p->next()) {
822 count++;
823 }
824 summary.add((double)count);
825 }
826 st->print_cr("StringTable statistics:");
827 st->print_cr("Number of buckets : %7d", summary.num());
828 st->print_cr("Average bucket size : %7.0f", summary.avg());
829 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
830 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
831 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
832 }
835 // Create a new table and using alternate hash code, populate the new table
836 // with the existing strings. Set flag to use the alternate hash code afterwards.
837 void StringTable::rehash_table() {
838 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
839 // This should never happen with -Xshare:dump but it might in testing mode.
840 if (DumpSharedSpaces) return;
841 StringTable* new_table = new StringTable();
843 // Rehash the table
844 the_table()->move_to(new_table);
846 // Delete the table and buckets (entries are reused in new table).
847 delete _the_table;
848 // Don't check if we need rehashing until the table gets unbalanced again.
849 // Then rehash with a new global seed.
850 _needs_rehashing = false;
851 _the_table = new_table;
852 }