Mon, 16 Jul 2012 19:50:52 -0700
Merge
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 */
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;
51 // Allocate symbols in the C heap when dumping shared spaces in case there
52 // are temporary symbols we can remove.
53 if (c_heap || DumpSharedSpaces) {
54 // refcount starts as 1
55 sym = new (len, THREAD) Symbol(name, len, 1);
56 } else {
57 sym = new (len, arena(), THREAD) Symbol(name, len, -1);
58 }
59 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
60 return sym;
61 }
63 void SymbolTable::initialize_symbols(int arena_alloc_size) {
64 // Initialize the arena for global symbols, size passed in depends on CDS.
65 if (arena_alloc_size == 0) {
66 _arena = new (mtSymbol) Arena();
67 } else {
68 _arena = new (mtSymbol) Arena(arena_alloc_size);
69 }
70 }
72 // Call function for all symbols in the symbol table.
73 void SymbolTable::symbols_do(SymbolClosure *cl) {
74 const int n = the_table()->table_size();
75 for (int i = 0; i < n; i++) {
76 for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
77 p != NULL;
78 p = p->next()) {
79 cl->do_symbol(p->literal_addr());
80 }
81 }
82 }
84 int SymbolTable::symbols_removed = 0;
85 int SymbolTable::symbols_counted = 0;
87 // Remove unreferenced symbols from the symbol table
88 // This is done late during GC.
89 void SymbolTable::unlink() {
90 int removed = 0;
91 int total = 0;
92 size_t memory_total = 0;
93 for (int i = 0; i < the_table()->table_size(); ++i) {
94 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
95 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
96 while (entry != NULL) {
97 // Shared entries are normally at the end of the bucket and if we run into
98 // a shared entry, then there is nothing more to remove. However, if we
99 // have rehashed the table, then the shared entries are no longer at the
100 // end of the bucket.
101 if (entry->is_shared() && !use_alternate_hashcode()) {
102 break;
103 }
104 Symbol* s = entry->literal();
105 memory_total += s->object_size();
106 total++;
107 assert(s != NULL, "just checking");
108 // If reference count is zero, remove.
109 if (s->refcount() == 0) {
110 assert(!entry->is_shared(), "shared entries should be kept live");
111 delete s;
112 removed++;
113 *p = entry->next();
114 the_table()->free_entry(entry);
115 } else {
116 p = entry->next_addr();
117 }
118 // get next entry
119 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
120 }
121 }
122 symbols_removed += removed;
123 symbols_counted += total;
124 // Exclude printing for normal PrintGCDetails because people parse
125 // this output.
126 if (PrintGCDetails && Verbose && WizardMode) {
127 gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", total,
128 (memory_total*HeapWordSize)/1024);
129 }
130 }
132 // Create a new table and using alternate hash code, populate the new table
133 // with the existing strings. Set flag to use the alternate hash code afterwards.
134 void SymbolTable::rehash_table() {
135 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
136 // This should never happen with -Xshare:dump but it might in testing mode.
137 if (DumpSharedSpaces) return;
138 // Create a new symbol table
139 SymbolTable* new_table = new SymbolTable();
141 the_table()->move_to(new_table);
143 // Delete the table and buckets (entries are reused in new table).
144 delete _the_table;
145 // Don't check if we need rehashing until the table gets unbalanced again.
146 // Then rehash with a new global seed.
147 _needs_rehashing = false;
148 _the_table = new_table;
149 }
151 // Lookup a symbol in a bucket.
153 Symbol* SymbolTable::lookup(int index, const char* name,
154 int len, unsigned int hash) {
155 int count = 0;
156 for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {
157 count++; // count all entries in this bucket, not just ones with same hash
158 if (e->hash() == hash) {
159 Symbol* sym = e->literal();
160 if (sym->equals(name, len)) {
161 // something is referencing this symbol now.
162 sym->increment_refcount();
163 return sym;
164 }
165 }
166 }
167 // If the bucket size is too deep check if this hash code is insufficient.
168 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
169 _needs_rehashing = check_rehash_table(count);
170 }
171 return NULL;
172 }
174 // Pick hashing algorithm.
175 unsigned int SymbolTable::hash_symbol(const char* s, int len) {
176 return use_alternate_hashcode() ?
177 AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :
178 java_lang_String::to_hash(s, len);
179 }
182 // We take care not to be blocking while holding the
183 // SymbolTable_lock. Otherwise, the system might deadlock, since the
184 // symboltable is used during compilation (VM_thread) The lock free
185 // synchronization is simplified by the fact that we do not delete
186 // entries in the symbol table during normal execution (only during
187 // safepoints).
189 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
190 unsigned int hashValue = hash_symbol(name, len);
191 int index = the_table()->hash_to_index(hashValue);
193 Symbol* s = the_table()->lookup(index, name, len, hashValue);
195 // Found
196 if (s != NULL) return s;
198 // Grab SymbolTable_lock first.
199 MutexLocker ml(SymbolTable_lock, THREAD);
201 // Otherwise, add to symbol to table
202 return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);
203 }
205 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
206 char* buffer;
207 int index, len;
208 unsigned int hashValue;
209 char* name;
210 {
211 debug_only(No_Safepoint_Verifier nsv;)
213 name = (char*)sym->base() + begin;
214 len = end - begin;
215 hashValue = hash_symbol(name, len);
216 index = the_table()->hash_to_index(hashValue);
217 Symbol* s = the_table()->lookup(index, name, len, hashValue);
219 // Found
220 if (s != NULL) return s;
221 }
223 // Otherwise, add to symbol to table. Copy to a C string first.
224 char stack_buf[128];
225 ResourceMark rm(THREAD);
226 if (len <= 128) {
227 buffer = stack_buf;
228 } else {
229 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
230 }
231 for (int i=0; i<len; i++) {
232 buffer[i] = name[i];
233 }
234 // Make sure there is no safepoint in the code above since name can't move.
235 // We can't include the code in No_Safepoint_Verifier because of the
236 // ResourceMark.
238 // Grab SymbolTable_lock first.
239 MutexLocker ml(SymbolTable_lock, THREAD);
241 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);
242 }
244 Symbol* SymbolTable::lookup_only(const char* name, int len,
245 unsigned int& hash) {
246 hash = hash_symbol(name, len);
247 int index = the_table()->hash_to_index(hash);
249 Symbol* s = the_table()->lookup(index, name, len, hash);
250 return s;
251 }
253 // Look up the address of the literal in the SymbolTable for this Symbol*
254 // Do not create any new symbols
255 // Do not increment the reference count to keep this alive
256 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){
257 unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());
258 int index = the_table()->hash_to_index(hash);
260 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {
261 if (e->hash() == hash) {
262 Symbol* literal_sym = e->literal();
263 if (sym == literal_sym) {
264 return e->literal_addr();
265 }
266 }
267 }
268 return NULL;
269 }
271 // Suggestion: Push unicode-based lookup all the way into the hashing
272 // and probing logic, so there is no need for convert_to_utf8 until
273 // an actual new Symbol* is created.
274 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
275 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
276 char stack_buf[128];
277 if (utf8_length < (int) sizeof(stack_buf)) {
278 char* chars = stack_buf;
279 UNICODE::convert_to_utf8(name, utf16_length, chars);
280 return lookup(chars, utf8_length, THREAD);
281 } else {
282 ResourceMark rm(THREAD);
283 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
284 UNICODE::convert_to_utf8(name, utf16_length, chars);
285 return lookup(chars, utf8_length, THREAD);
286 }
287 }
289 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
290 unsigned int& hash) {
291 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
292 char stack_buf[128];
293 if (utf8_length < (int) sizeof(stack_buf)) {
294 char* chars = stack_buf;
295 UNICODE::convert_to_utf8(name, utf16_length, chars);
296 return lookup_only(chars, utf8_length, hash);
297 } else {
298 ResourceMark rm;
299 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
300 UNICODE::convert_to_utf8(name, utf16_length, chars);
301 return lookup_only(chars, utf8_length, hash);
302 }
303 }
305 void SymbolTable::add(Handle class_loader, constantPoolHandle cp,
306 int names_count,
307 const char** names, int* lengths, int* cp_indices,
308 unsigned int* hashValues, TRAPS) {
309 // Grab SymbolTable_lock first.
310 MutexLocker ml(SymbolTable_lock, THREAD);
312 SymbolTable* table = the_table();
313 bool added = table->basic_add(class_loader, cp, names_count, names, lengths,
314 cp_indices, hashValues, CHECK);
315 if (!added) {
316 // do it the hard way
317 for (int i=0; i<names_count; i++) {
318 int index = table->hash_to_index(hashValues[i]);
319 bool c_heap = class_loader() != NULL;
320 Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);
321 cp->symbol_at_put(cp_indices[i], sym);
322 }
323 }
324 }
326 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
327 unsigned int hash;
328 Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);
329 if (result != NULL) {
330 return result;
331 }
332 // Grab SymbolTable_lock first.
333 MutexLocker ml(SymbolTable_lock, THREAD);
335 SymbolTable* table = the_table();
336 int index = table->hash_to_index(hash);
337 return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);
338 }
340 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,
341 unsigned int hashValue_arg, bool c_heap, TRAPS) {
342 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
343 "proposed name of symbol must be stable");
345 // Don't allow symbols to be created which cannot fit in a Symbol*.
346 if (len > Symbol::max_length()) {
347 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
348 "name is too long to represent");
349 }
351 // Cannot hit a safepoint in this function because the "this" pointer can move.
352 No_Safepoint_Verifier nsv;
354 // Check if the symbol table has been rehashed, if so, need to recalculate
355 // the hash value and index.
356 unsigned int hashValue;
357 int index;
358 if (use_alternate_hashcode()) {
359 hashValue = hash_symbol((const char*)name, len);
360 index = hash_to_index(hashValue);
361 } else {
362 hashValue = hashValue_arg;
363 index = index_arg;
364 }
366 // Since look-up was done lock-free, we need to check if another
367 // thread beat us in the race to insert the symbol.
368 Symbol* test = lookup(index, (char*)name, len, hashValue);
369 if (test != NULL) {
370 // A race occurred and another thread introduced the symbol.
371 assert(test->refcount() != 0, "lookup should have incremented the count");
372 return test;
373 }
375 // Create a new symbol.
376 Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);
377 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
379 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
380 add_entry(index, entry);
381 return sym;
382 }
384 // This version of basic_add adds symbols in batch from the constant pool
385 // parsing.
386 bool SymbolTable::basic_add(Handle class_loader, constantPoolHandle cp,
387 int names_count,
388 const char** names, int* lengths,
389 int* cp_indices, unsigned int* hashValues,
390 TRAPS) {
392 // Check symbol names are not too long. If any are too long, don't add any.
393 for (int i = 0; i< names_count; i++) {
394 if (lengths[i] > Symbol::max_length()) {
395 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
396 "name is too long to represent");
397 }
398 }
400 // Cannot hit a safepoint in this function because the "this" pointer can move.
401 No_Safepoint_Verifier nsv;
403 for (int i=0; i<names_count; i++) {
404 // Check if the symbol table has been rehashed, if so, need to recalculate
405 // the hash value.
406 unsigned int hashValue;
407 if (use_alternate_hashcode()) {
408 hashValue = hash_symbol(names[i], lengths[i]);
409 } else {
410 hashValue = hashValues[i];
411 }
412 // Since look-up was done lock-free, we need to check if another
413 // thread beat us in the race to insert the symbol.
414 int index = hash_to_index(hashValue);
415 Symbol* test = lookup(index, names[i], lengths[i], hashValue);
416 if (test != NULL) {
417 // A race occurred and another thread introduced the symbol, this one
418 // will be dropped and collected. Use test instead.
419 cp->symbol_at_put(cp_indices[i], test);
420 assert(test->refcount() != 0, "lookup should have incremented the count");
421 } else {
422 // Create a new symbol. The null class loader is never unloaded so these
423 // are allocated specially in a permanent arena.
424 bool c_heap = class_loader() != NULL;
425 Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));
426 assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized"); // why wouldn't it be???
427 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
428 add_entry(index, entry);
429 cp->symbol_at_put(cp_indices[i], sym);
430 }
431 }
432 return true;
433 }
436 void SymbolTable::verify() {
437 for (int i = 0; i < the_table()->table_size(); ++i) {
438 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
439 for ( ; p != NULL; p = p->next()) {
440 Symbol* s = (Symbol*)(p->literal());
441 guarantee(s != NULL, "symbol is NULL");
442 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
443 guarantee(p->hash() == h, "broken hash in symbol table entry");
444 guarantee(the_table()->hash_to_index(h) == i,
445 "wrong index in symbol table");
446 }
447 }
448 }
450 void SymbolTable::dump(outputStream* st) {
451 NumberSeq summary;
452 for (int i = 0; i < the_table()->table_size(); ++i) {
453 int count = 0;
454 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(i);
455 e != NULL; e = e->next()) {
456 count++;
457 }
458 summary.add((double)count);
459 }
460 st->print_cr("SymbolTable statistics:");
461 st->print_cr("Number of buckets : %7d", summary.num());
462 st->print_cr("Average bucket size : %7.0f", summary.avg());
463 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
464 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
465 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
466 }
469 //---------------------------------------------------------------------------
470 // Non-product code
472 #ifndef PRODUCT
474 void SymbolTable::print_histogram() {
475 MutexLocker ml(SymbolTable_lock);
476 const int results_length = 100;
477 int results[results_length];
478 int i,j;
480 // initialize results to zero
481 for (j = 0; j < results_length; j++) {
482 results[j] = 0;
483 }
485 int total = 0;
486 int max_symbols = 0;
487 int out_of_range = 0;
488 int memory_total = 0;
489 int count = 0;
490 for (i = 0; i < the_table()->table_size(); i++) {
491 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
492 for ( ; p != NULL; p = p->next()) {
493 memory_total += p->literal()->object_size();
494 count++;
495 int counter = p->literal()->utf8_length();
496 total += counter;
497 if (counter < results_length) {
498 results[counter]++;
499 } else {
500 out_of_range++;
501 }
502 max_symbols = MAX2(max_symbols, counter);
503 }
504 }
505 tty->print_cr("Symbol Table:");
506 tty->print_cr("Total number of symbols %5d", count);
507 tty->print_cr("Total size in memory %5dK",
508 (memory_total*HeapWordSize)/1024);
509 tty->print_cr("Total counted %5d", symbols_counted);
510 tty->print_cr("Total removed %5d", symbols_removed);
511 if (symbols_counted > 0) {
512 tty->print_cr("Percent removed %3.2f",
513 ((float)symbols_removed/(float)symbols_counted)* 100);
514 }
515 tty->print_cr("Reference counts %5d", Symbol::_total_count);
516 tty->print_cr("Symbol arena size %5d used %5d",
517 arena()->size_in_bytes(), arena()->used());
518 tty->print_cr("Histogram of symbol length:");
519 tty->print_cr("%8s %5d", "Total ", total);
520 tty->print_cr("%8s %5d", "Maximum", max_symbols);
521 tty->print_cr("%8s %3.2f", "Average",
522 ((float) total / (float) the_table()->table_size()));
523 tty->print_cr("%s", "Histogram:");
524 tty->print_cr(" %s %29s", "Length", "Number chains that length");
525 for (i = 0; i < results_length; i++) {
526 if (results[i] > 0) {
527 tty->print_cr("%6d %10d", i, results[i]);
528 }
529 }
530 if (Verbose) {
531 int line_length = 70;
532 tty->print_cr("%s %30s", " Length", "Number chains that length");
533 for (i = 0; i < results_length; i++) {
534 if (results[i] > 0) {
535 tty->print("%4d", i);
536 for (j = 0; (j < results[i]) && (j < line_length); j++) {
537 tty->print("%1s", "*");
538 }
539 if (j == line_length) {
540 tty->print("%1s", "+");
541 }
542 tty->cr();
543 }
544 }
545 }
546 tty->print_cr(" %s %d: %d\n", "Number chains longer than",
547 results_length, out_of_range);
548 }
550 void SymbolTable::print() {
551 for (int i = 0; i < the_table()->table_size(); ++i) {
552 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
553 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
554 if (entry != NULL) {
555 while (entry != NULL) {
556 tty->print(PTR_FORMAT " ", entry->literal());
557 entry->literal()->print();
558 tty->print(" %d", entry->literal()->refcount());
559 p = entry->next_addr();
560 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
561 }
562 tty->cr();
563 }
564 }
565 }
566 #endif // PRODUCT
568 // --------------------------------------------------------------------------
570 #ifdef ASSERT
571 class StableMemoryChecker : public StackObj {
572 enum { _bufsize = wordSize*4 };
574 address _region;
575 jint _size;
576 u1 _save_buf[_bufsize];
578 int sample(u1* save_buf) {
579 if (_size <= _bufsize) {
580 memcpy(save_buf, _region, _size);
581 return _size;
582 } else {
583 // copy head and tail
584 memcpy(&save_buf[0], _region, _bufsize/2);
585 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
586 return (_bufsize/2)*2;
587 }
588 }
590 public:
591 StableMemoryChecker(const void* region, jint size) {
592 _region = (address) region;
593 _size = size;
594 sample(_save_buf);
595 }
597 bool verify() {
598 u1 check_buf[sizeof(_save_buf)];
599 int check_size = sample(check_buf);
600 return (0 == memcmp(_save_buf, check_buf, check_size));
601 }
603 void set_region(const void* region) { _region = (address) region; }
604 };
605 #endif
608 // --------------------------------------------------------------------------
609 StringTable* StringTable::_the_table = NULL;
611 bool StringTable::_needs_rehashing = false;
613 // Pick hashing algorithm
614 unsigned int StringTable::hash_string(const jchar* s, int len) {
615 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
616 java_lang_String::to_hash(s, len);
617 }
619 oop StringTable::lookup(int index, jchar* name,
620 int len, unsigned int hash) {
621 int count = 0;
622 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
623 count++;
624 if (l->hash() == hash) {
625 if (java_lang_String::equals(l->literal(), name, len)) {
626 return l->literal();
627 }
628 }
629 }
630 // If the bucket size is too deep check if this hash code is insufficient.
631 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
632 _needs_rehashing = check_rehash_table(count);
633 }
634 return NULL;
635 }
638 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
639 int len, unsigned int hashValue_arg, TRAPS) {
641 assert(java_lang_String::equals(string(), name, len),
642 "string must be properly initialized");
643 // Cannot hit a safepoint in this function because the "this" pointer can move.
644 No_Safepoint_Verifier nsv;
646 // Check if the symbol table has been rehashed, if so, need to recalculate
647 // the hash value and index before second lookup.
648 unsigned int hashValue;
649 int index;
650 if (use_alternate_hashcode()) {
651 hashValue = hash_string(name, len);
652 index = hash_to_index(hashValue);
653 } else {
654 hashValue = hashValue_arg;
655 index = index_arg;
656 }
658 // Since look-up was done lock-free, we need to check if another
659 // thread beat us in the race to insert the symbol.
661 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
662 if (test != NULL) {
663 // Entry already added
664 return test;
665 }
667 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
668 add_entry(index, entry);
669 return string();
670 }
673 oop StringTable::lookup(Symbol* symbol) {
674 ResourceMark rm;
675 int length;
676 jchar* chars = symbol->as_unicode(length);
677 unsigned int hashValue = hash_string(chars, length);
678 int index = the_table()->hash_to_index(hashValue);
679 return the_table()->lookup(index, chars, length, hashValue);
680 }
683 oop StringTable::intern(Handle string_or_null, jchar* name,
684 int len, TRAPS) {
685 unsigned int hashValue = hash_string(name, len);
686 int index = the_table()->hash_to_index(hashValue);
687 oop found_string = the_table()->lookup(index, name, len, hashValue);
689 // Found
690 if (found_string != NULL) return found_string;
692 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
693 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
694 "proposed name of symbol must be stable");
696 Handle string;
697 // try to reuse the string if possible
698 if (!string_or_null.is_null() && (!JavaObjectsInPerm || string_or_null()->is_perm())) {
699 string = string_or_null;
700 } else {
701 string = java_lang_String::create_tenured_from_unicode(name, len, CHECK_NULL);
702 }
704 // Grab the StringTable_lock before getting the_table() because it could
705 // change at safepoint.
706 MutexLocker ml(StringTable_lock, THREAD);
708 // Otherwise, add to symbol to table
709 return the_table()->basic_add(index, string, name, len,
710 hashValue, CHECK_NULL);
711 }
713 oop StringTable::intern(Symbol* symbol, TRAPS) {
714 if (symbol == NULL) return NULL;
715 ResourceMark rm(THREAD);
716 int length;
717 jchar* chars = symbol->as_unicode(length);
718 Handle string;
719 oop result = intern(string, chars, length, CHECK_NULL);
720 return result;
721 }
724 oop StringTable::intern(oop string, TRAPS)
725 {
726 if (string == NULL) return NULL;
727 ResourceMark rm(THREAD);
728 int length;
729 Handle h_string (THREAD, string);
730 jchar* chars = java_lang_String::as_unicode_string(string, length);
731 oop result = intern(h_string, chars, length, CHECK_NULL);
732 return result;
733 }
736 oop StringTable::intern(const char* utf8_string, TRAPS) {
737 if (utf8_string == NULL) return NULL;
738 ResourceMark rm(THREAD);
739 int length = UTF8::unicode_length(utf8_string);
740 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
741 UTF8::convert_to_unicode(utf8_string, chars, length);
742 Handle string;
743 oop result = intern(string, chars, length, CHECK_NULL);
744 return result;
745 }
747 void StringTable::unlink(BoolObjectClosure* is_alive) {
748 // Readers of the table are unlocked, so we should only be removing
749 // entries at a safepoint.
750 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
751 for (int i = 0; i < the_table()->table_size(); ++i) {
752 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
753 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
754 while (entry != NULL) {
755 // Shared entries are normally at the end of the bucket and if we run into
756 // a shared entry, then there is nothing more to remove. However, if we
757 // have rehashed the table, then the shared entries are no longer at the
758 // end of the bucket.
759 if (entry->is_shared() && !use_alternate_hashcode()) {
760 break;
761 }
762 assert(entry->literal() != NULL, "just checking");
763 if (entry->is_shared() || is_alive->do_object_b(entry->literal())) {
764 p = entry->next_addr();
765 } else {
766 *p = entry->next();
767 the_table()->free_entry(entry);
768 }
769 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
770 }
771 }
772 }
774 void StringTable::oops_do(OopClosure* f) {
775 for (int i = 0; i < the_table()->table_size(); ++i) {
776 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
777 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
778 while (entry != NULL) {
779 f->do_oop((oop*)entry->literal_addr());
781 // Did the closure remove the literal from the table?
782 if (entry->literal() == NULL) {
783 assert(!entry->is_shared(), "immutable hashtable entry?");
784 *p = entry->next();
785 the_table()->free_entry(entry);
786 } else {
787 p = entry->next_addr();
788 }
789 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
790 }
791 }
792 }
794 void StringTable::verify() {
795 for (int i = 0; i < the_table()->table_size(); ++i) {
796 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
797 for ( ; p != NULL; p = p->next()) {
798 oop s = p->literal();
799 guarantee(s != NULL, "interned string is NULL");
800 guarantee(s->is_perm() || !JavaObjectsInPerm, "interned string not in permspace");
801 unsigned int h = java_lang_String::hash_string(s);
802 guarantee(p->hash() == h, "broken hash in string table entry");
803 guarantee(the_table()->hash_to_index(h) == i,
804 "wrong index in string table");
805 }
806 }
807 }
809 void StringTable::dump(outputStream* st) {
810 NumberSeq summary;
811 for (int i = 0; i < the_table()->table_size(); ++i) {
812 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
813 int count = 0;
814 for ( ; p != NULL; p = p->next()) {
815 count++;
816 }
817 summary.add((double)count);
818 }
819 st->print_cr("StringTable statistics:");
820 st->print_cr("Number of buckets : %7d", summary.num());
821 st->print_cr("Average bucket size : %7.0f", summary.avg());
822 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
823 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
824 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
825 }
828 // Create a new table and using alternate hash code, populate the new table
829 // with the existing strings. Set flag to use the alternate hash code afterwards.
830 void StringTable::rehash_table() {
831 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
832 // This should never happen with -Xshare:dump but it might in testing mode.
833 if (DumpSharedSpaces) return;
834 StringTable* new_table = new StringTable();
836 // Rehash the table
837 the_table()->move_to(new_table);
839 // Delete the table and buckets (entries are reused in new table).
840 delete _the_table;
841 // Don't check if we need rehashing until the table gets unbalanced again.
842 // Then rehash with a new global seed.
843 _needs_rehashing = false;
844 _the_table = new_table;
845 }