Thu, 28 Jun 2012 17:03:16 -0400
6995781: Native Memory Tracking (Phase 1)
7151532: DCmd for hotspot native memory tracking
Summary: Implementation of native memory tracking phase 1, which tracks VM native memory usage, and related DCmd
Reviewed-by: acorn, coleenp, fparain
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;
46 jint SymbolTable::_seed = 0;
48 Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) {
49 assert (len <= Symbol::max_length(), "should be checked by caller");
51 Symbol* sym;
52 // Allocate symbols in the C heap when dumping shared spaces in case there
53 // are temporary symbols we can remove.
54 if (c_heap || DumpSharedSpaces) {
55 // refcount starts as 1
56 sym = new (len, THREAD) Symbol(name, len, 1);
57 } else {
58 sym = new (len, arena(), THREAD) Symbol(name, len, -1);
59 }
60 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
61 return sym;
62 }
64 void SymbolTable::initialize_symbols(int arena_alloc_size) {
65 // Initialize the arena for global symbols, size passed in depends on CDS.
66 if (arena_alloc_size == 0) {
67 _arena = new (mtSymbol) Arena();
68 } else {
69 _arena = new (mtSymbol) Arena(arena_alloc_size);
70 }
71 }
73 // Call function for all symbols in the symbol table.
74 void SymbolTable::symbols_do(SymbolClosure *cl) {
75 const int n = the_table()->table_size();
76 for (int i = 0; i < n; i++) {
77 for (HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
78 p != NULL;
79 p = p->next()) {
80 cl->do_symbol(p->literal_addr());
81 }
82 }
83 }
85 int SymbolTable::symbols_removed = 0;
86 int SymbolTable::symbols_counted = 0;
88 // Remove unreferenced symbols from the symbol table
89 // This is done late during GC.
90 void SymbolTable::unlink() {
91 int removed = 0;
92 int total = 0;
93 size_t memory_total = 0;
94 for (int i = 0; i < the_table()->table_size(); ++i) {
95 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
96 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
97 while (entry != NULL) {
98 // Shared entries are normally at the end of the bucket and if we run into
99 // a shared entry, then there is nothing more to remove. However, if we
100 // have rehashed the table, then the shared entries are no longer at the
101 // end of the bucket.
102 if (entry->is_shared() && !use_alternate_hashcode()) {
103 break;
104 }
105 Symbol* s = entry->literal();
106 memory_total += s->object_size();
107 total++;
108 assert(s != NULL, "just checking");
109 // If reference count is zero, remove.
110 if (s->refcount() == 0) {
111 assert(!entry->is_shared(), "shared entries should be kept live");
112 delete s;
113 removed++;
114 *p = entry->next();
115 the_table()->free_entry(entry);
116 } else {
117 p = entry->next_addr();
118 }
119 // get next entry
120 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
121 }
122 }
123 symbols_removed += removed;
124 symbols_counted += total;
125 // Exclude printing for normal PrintGCDetails because people parse
126 // this output.
127 if (PrintGCDetails && Verbose && WizardMode) {
128 gclog_or_tty->print(" [Symbols=%d size=" SIZE_FORMAT "K] ", total,
129 (memory_total*HeapWordSize)/1024);
130 }
131 }
133 unsigned int SymbolTable::new_hash(Symbol* sym) {
134 ResourceMark rm;
135 // Use alternate hashing algorithm on this symbol.
136 return AltHashing::murmur3_32(seed(), (const jbyte*)sym->as_C_string(), sym->utf8_length());
137 }
139 // Create a new table and using alternate hash code, populate the new table
140 // with the existing strings. Set flag to use the alternate hash code afterwards.
141 void SymbolTable::rehash_table() {
142 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
143 // This should never happen with -Xshare:dump but it might in testing mode.
144 if (DumpSharedSpaces) return;
145 // Create a new symbol table
146 SymbolTable* new_table = new SymbolTable();
148 // Initialize the global seed for hashing.
149 _seed = AltHashing::compute_seed();
150 assert(seed() != 0, "shouldn't be zero");
152 the_table()->move_to(new_table);
154 // Delete the table and buckets (entries are reused in new table).
155 delete _the_table;
156 // Don't check if we need rehashing until the table gets unbalanced again.
157 // Then rehash with a new global seed.
158 _needs_rehashing = false;
159 _the_table = new_table;
160 }
162 // Lookup a symbol in a bucket.
164 Symbol* SymbolTable::lookup(int index, const char* name,
165 int len, unsigned int hash) {
166 int count = 0;
167 for (HashtableEntry<Symbol*, mtSymbol>* e = bucket(index); e != NULL; e = e->next()) {
168 count++; // count all entries in this bucket, not just ones with same hash
169 if (e->hash() == hash) {
170 Symbol* sym = e->literal();
171 if (sym->equals(name, len)) {
172 // something is referencing this symbol now.
173 sym->increment_refcount();
174 return sym;
175 }
176 }
177 }
178 // If the bucket size is too deep check if this hash code is insufficient.
179 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
180 _needs_rehashing = check_rehash_table(count);
181 }
182 return NULL;
183 }
185 // Pick hashing algorithm.
186 unsigned int SymbolTable::hash_symbol(const char* s, int len) {
187 return use_alternate_hashcode() ?
188 AltHashing::murmur3_32(seed(), (const jbyte*)s, len) :
189 java_lang_String::to_hash(s, len);
190 }
193 // We take care not to be blocking while holding the
194 // SymbolTable_lock. Otherwise, the system might deadlock, since the
195 // symboltable is used during compilation (VM_thread) The lock free
196 // synchronization is simplified by the fact that we do not delete
197 // entries in the symbol table during normal execution (only during
198 // safepoints).
200 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
201 unsigned int hashValue = hash_symbol(name, len);
202 int index = the_table()->hash_to_index(hashValue);
204 Symbol* s = the_table()->lookup(index, name, len, hashValue);
206 // Found
207 if (s != NULL) return s;
209 // Grab SymbolTable_lock first.
210 MutexLocker ml(SymbolTable_lock, THREAD);
212 // Otherwise, add to symbol to table
213 return the_table()->basic_add(index, (u1*)name, len, hashValue, true, CHECK_NULL);
214 }
216 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
217 char* buffer;
218 int index, len;
219 unsigned int hashValue;
220 char* name;
221 {
222 debug_only(No_Safepoint_Verifier nsv;)
224 name = (char*)sym->base() + begin;
225 len = end - begin;
226 hashValue = hash_symbol(name, len);
227 index = the_table()->hash_to_index(hashValue);
228 Symbol* s = the_table()->lookup(index, name, len, hashValue);
230 // Found
231 if (s != NULL) return s;
232 }
234 // Otherwise, add to symbol to table. Copy to a C string first.
235 char stack_buf[128];
236 ResourceMark rm(THREAD);
237 if (len <= 128) {
238 buffer = stack_buf;
239 } else {
240 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
241 }
242 for (int i=0; i<len; i++) {
243 buffer[i] = name[i];
244 }
245 // Make sure there is no safepoint in the code above since name can't move.
246 // We can't include the code in No_Safepoint_Verifier because of the
247 // ResourceMark.
249 // Grab SymbolTable_lock first.
250 MutexLocker ml(SymbolTable_lock, THREAD);
252 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, true, CHECK_NULL);
253 }
255 Symbol* SymbolTable::lookup_only(const char* name, int len,
256 unsigned int& hash) {
257 hash = hash_symbol(name, len);
258 int index = the_table()->hash_to_index(hash);
260 Symbol* s = the_table()->lookup(index, name, len, hash);
261 return s;
262 }
264 // Look up the address of the literal in the SymbolTable for this Symbol*
265 // Do not create any new symbols
266 // Do not increment the reference count to keep this alive
267 Symbol** SymbolTable::lookup_symbol_addr(Symbol* sym){
268 unsigned int hash = hash_symbol((char*)sym->bytes(), sym->utf8_length());
269 int index = the_table()->hash_to_index(hash);
271 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(index); e != NULL; e = e->next()) {
272 if (e->hash() == hash) {
273 Symbol* literal_sym = e->literal();
274 if (sym == literal_sym) {
275 return e->literal_addr();
276 }
277 }
278 }
279 return NULL;
280 }
282 // Suggestion: Push unicode-based lookup all the way into the hashing
283 // and probing logic, so there is no need for convert_to_utf8 until
284 // an actual new Symbol* is created.
285 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
286 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
287 char stack_buf[128];
288 if (utf8_length < (int) sizeof(stack_buf)) {
289 char* chars = stack_buf;
290 UNICODE::convert_to_utf8(name, utf16_length, chars);
291 return lookup(chars, utf8_length, THREAD);
292 } else {
293 ResourceMark rm(THREAD);
294 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
295 UNICODE::convert_to_utf8(name, utf16_length, chars);
296 return lookup(chars, utf8_length, THREAD);
297 }
298 }
300 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
301 unsigned int& hash) {
302 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
303 char stack_buf[128];
304 if (utf8_length < (int) sizeof(stack_buf)) {
305 char* chars = stack_buf;
306 UNICODE::convert_to_utf8(name, utf16_length, chars);
307 return lookup_only(chars, utf8_length, hash);
308 } else {
309 ResourceMark rm;
310 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
311 UNICODE::convert_to_utf8(name, utf16_length, chars);
312 return lookup_only(chars, utf8_length, hash);
313 }
314 }
316 void SymbolTable::add(Handle class_loader, constantPoolHandle cp,
317 int names_count,
318 const char** names, int* lengths, int* cp_indices,
319 unsigned int* hashValues, TRAPS) {
320 // Grab SymbolTable_lock first.
321 MutexLocker ml(SymbolTable_lock, THREAD);
323 SymbolTable* table = the_table();
324 bool added = table->basic_add(class_loader, cp, names_count, names, lengths,
325 cp_indices, hashValues, CHECK);
326 if (!added) {
327 // do it the hard way
328 for (int i=0; i<names_count; i++) {
329 int index = table->hash_to_index(hashValues[i]);
330 bool c_heap = class_loader() != NULL;
331 Symbol* sym = table->basic_add(index, (u1*)names[i], lengths[i], hashValues[i], c_heap, CHECK);
332 cp->symbol_at_put(cp_indices[i], sym);
333 }
334 }
335 }
337 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
338 unsigned int hash;
339 Symbol* result = SymbolTable::lookup_only((char*)name, (int)strlen(name), hash);
340 if (result != NULL) {
341 return result;
342 }
343 // Grab SymbolTable_lock first.
344 MutexLocker ml(SymbolTable_lock, THREAD);
346 SymbolTable* table = the_table();
347 int index = table->hash_to_index(hash);
348 return table->basic_add(index, (u1*)name, (int)strlen(name), hash, false, THREAD);
349 }
351 Symbol* SymbolTable::basic_add(int index_arg, u1 *name, int len,
352 unsigned int hashValue_arg, bool c_heap, TRAPS) {
353 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
354 "proposed name of symbol must be stable");
356 // Don't allow symbols to be created which cannot fit in a Symbol*.
357 if (len > Symbol::max_length()) {
358 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
359 "name is too long to represent");
360 }
362 // Cannot hit a safepoint in this function because the "this" pointer can move.
363 No_Safepoint_Verifier nsv;
365 // Check if the symbol table has been rehashed, if so, need to recalculate
366 // the hash value and index.
367 unsigned int hashValue;
368 int index;
369 if (use_alternate_hashcode()) {
370 hashValue = hash_symbol((const char*)name, len);
371 index = hash_to_index(hashValue);
372 } else {
373 hashValue = hashValue_arg;
374 index = index_arg;
375 }
377 // Since look-up was done lock-free, we need to check if another
378 // thread beat us in the race to insert the symbol.
379 Symbol* test = lookup(index, (char*)name, len, hashValue);
380 if (test != NULL) {
381 // A race occurred and another thread introduced the symbol.
382 assert(test->refcount() != 0, "lookup should have incremented the count");
383 return test;
384 }
386 // Create a new symbol.
387 Symbol* sym = allocate_symbol(name, len, c_heap, CHECK_NULL);
388 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
390 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
391 add_entry(index, entry);
392 return sym;
393 }
395 // This version of basic_add adds symbols in batch from the constant pool
396 // parsing.
397 bool SymbolTable::basic_add(Handle class_loader, constantPoolHandle cp,
398 int names_count,
399 const char** names, int* lengths,
400 int* cp_indices, unsigned int* hashValues,
401 TRAPS) {
403 // Check symbol names are not too long. If any are too long, don't add any.
404 for (int i = 0; i< names_count; i++) {
405 if (lengths[i] > Symbol::max_length()) {
406 THROW_MSG_0(vmSymbols::java_lang_InternalError(),
407 "name is too long to represent");
408 }
409 }
411 // Cannot hit a safepoint in this function because the "this" pointer can move.
412 No_Safepoint_Verifier nsv;
414 for (int i=0; i<names_count; i++) {
415 // Check if the symbol table has been rehashed, if so, need to recalculate
416 // the hash value.
417 unsigned int hashValue;
418 if (use_alternate_hashcode()) {
419 hashValue = hash_symbol(names[i], lengths[i]);
420 } else {
421 hashValue = hashValues[i];
422 }
423 // Since look-up was done lock-free, we need to check if another
424 // thread beat us in the race to insert the symbol.
425 int index = hash_to_index(hashValue);
426 Symbol* test = lookup(index, names[i], lengths[i], hashValue);
427 if (test != NULL) {
428 // A race occurred and another thread introduced the symbol, this one
429 // will be dropped and collected. Use test instead.
430 cp->symbol_at_put(cp_indices[i], test);
431 assert(test->refcount() != 0, "lookup should have incremented the count");
432 } else {
433 // Create a new symbol. The null class loader is never unloaded so these
434 // are allocated specially in a permanent arena.
435 bool c_heap = class_loader() != NULL;
436 Symbol* sym = allocate_symbol((const u1*)names[i], lengths[i], c_heap, CHECK_(false));
437 assert(sym->equals(names[i], lengths[i]), "symbol must be properly initialized"); // why wouldn't it be???
438 HashtableEntry<Symbol*, mtSymbol>* entry = new_entry(hashValue, sym);
439 add_entry(index, entry);
440 cp->symbol_at_put(cp_indices[i], sym);
441 }
442 }
443 return true;
444 }
447 void SymbolTable::verify() {
448 for (int i = 0; i < the_table()->table_size(); ++i) {
449 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
450 for ( ; p != NULL; p = p->next()) {
451 Symbol* s = (Symbol*)(p->literal());
452 guarantee(s != NULL, "symbol is NULL");
453 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
454 guarantee(p->hash() == h, "broken hash in symbol table entry");
455 guarantee(the_table()->hash_to_index(h) == i,
456 "wrong index in symbol table");
457 }
458 }
459 }
461 void SymbolTable::dump(outputStream* st) {
462 NumberSeq summary;
463 for (int i = 0; i < the_table()->table_size(); ++i) {
464 int count = 0;
465 for (HashtableEntry<Symbol*, mtSymbol>* e = the_table()->bucket(i);
466 e != NULL; e = e->next()) {
467 count++;
468 }
469 summary.add((double)count);
470 }
471 st->print_cr("SymbolTable statistics:");
472 st->print_cr("Number of buckets : %7d", summary.num());
473 st->print_cr("Average bucket size : %7.0f", summary.avg());
474 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
475 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
476 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
477 }
480 //---------------------------------------------------------------------------
481 // Non-product code
483 #ifndef PRODUCT
485 void SymbolTable::print_histogram() {
486 MutexLocker ml(SymbolTable_lock);
487 const int results_length = 100;
488 int results[results_length];
489 int i,j;
491 // initialize results to zero
492 for (j = 0; j < results_length; j++) {
493 results[j] = 0;
494 }
496 int total = 0;
497 int max_symbols = 0;
498 int out_of_range = 0;
499 int memory_total = 0;
500 int count = 0;
501 for (i = 0; i < the_table()->table_size(); i++) {
502 HashtableEntry<Symbol*, mtSymbol>* p = the_table()->bucket(i);
503 for ( ; p != NULL; p = p->next()) {
504 memory_total += p->literal()->object_size();
505 count++;
506 int counter = p->literal()->utf8_length();
507 total += counter;
508 if (counter < results_length) {
509 results[counter]++;
510 } else {
511 out_of_range++;
512 }
513 max_symbols = MAX2(max_symbols, counter);
514 }
515 }
516 tty->print_cr("Symbol Table:");
517 tty->print_cr("Total number of symbols %5d", count);
518 tty->print_cr("Total size in memory %5dK",
519 (memory_total*HeapWordSize)/1024);
520 tty->print_cr("Total counted %5d", symbols_counted);
521 tty->print_cr("Total removed %5d", symbols_removed);
522 if (symbols_counted > 0) {
523 tty->print_cr("Percent removed %3.2f",
524 ((float)symbols_removed/(float)symbols_counted)* 100);
525 }
526 tty->print_cr("Reference counts %5d", Symbol::_total_count);
527 tty->print_cr("Symbol arena size %5d used %5d",
528 arena()->size_in_bytes(), arena()->used());
529 tty->print_cr("Histogram of symbol length:");
530 tty->print_cr("%8s %5d", "Total ", total);
531 tty->print_cr("%8s %5d", "Maximum", max_symbols);
532 tty->print_cr("%8s %3.2f", "Average",
533 ((float) total / (float) the_table()->table_size()));
534 tty->print_cr("%s", "Histogram:");
535 tty->print_cr(" %s %29s", "Length", "Number chains that length");
536 for (i = 0; i < results_length; i++) {
537 if (results[i] > 0) {
538 tty->print_cr("%6d %10d", i, results[i]);
539 }
540 }
541 if (Verbose) {
542 int line_length = 70;
543 tty->print_cr("%s %30s", " Length", "Number chains that length");
544 for (i = 0; i < results_length; i++) {
545 if (results[i] > 0) {
546 tty->print("%4d", i);
547 for (j = 0; (j < results[i]) && (j < line_length); j++) {
548 tty->print("%1s", "*");
549 }
550 if (j == line_length) {
551 tty->print("%1s", "+");
552 }
553 tty->cr();
554 }
555 }
556 }
557 tty->print_cr(" %s %d: %d\n", "Number chains longer than",
558 results_length, out_of_range);
559 }
561 void SymbolTable::print() {
562 for (int i = 0; i < the_table()->table_size(); ++i) {
563 HashtableEntry<Symbol*, mtSymbol>** p = the_table()->bucket_addr(i);
564 HashtableEntry<Symbol*, mtSymbol>* entry = the_table()->bucket(i);
565 if (entry != NULL) {
566 while (entry != NULL) {
567 tty->print(PTR_FORMAT " ", entry->literal());
568 entry->literal()->print();
569 tty->print(" %d", entry->literal()->refcount());
570 p = entry->next_addr();
571 entry = (HashtableEntry<Symbol*, mtSymbol>*)HashtableEntry<Symbol*, mtSymbol>::make_ptr(*p);
572 }
573 tty->cr();
574 }
575 }
576 }
577 #endif // PRODUCT
579 // --------------------------------------------------------------------------
581 #ifdef ASSERT
582 class StableMemoryChecker : public StackObj {
583 enum { _bufsize = wordSize*4 };
585 address _region;
586 jint _size;
587 u1 _save_buf[_bufsize];
589 int sample(u1* save_buf) {
590 if (_size <= _bufsize) {
591 memcpy(save_buf, _region, _size);
592 return _size;
593 } else {
594 // copy head and tail
595 memcpy(&save_buf[0], _region, _bufsize/2);
596 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
597 return (_bufsize/2)*2;
598 }
599 }
601 public:
602 StableMemoryChecker(const void* region, jint size) {
603 _region = (address) region;
604 _size = size;
605 sample(_save_buf);
606 }
608 bool verify() {
609 u1 check_buf[sizeof(_save_buf)];
610 int check_size = sample(check_buf);
611 return (0 == memcmp(_save_buf, check_buf, check_size));
612 }
614 void set_region(const void* region) { _region = (address) region; }
615 };
616 #endif
619 // --------------------------------------------------------------------------
620 StringTable* StringTable::_the_table = NULL;
622 bool StringTable::_needs_rehashing = false;
623 jint StringTable::_seed = 0;
625 // Pick hashing algorithm
626 unsigned int StringTable::hash_string(const jchar* s, int len) {
627 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
628 java_lang_String::to_hash(s, len);
629 }
631 oop StringTable::lookup(int index, jchar* name,
632 int len, unsigned int hash) {
633 int count = 0;
634 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
635 count++;
636 if (l->hash() == hash) {
637 if (java_lang_String::equals(l->literal(), name, len)) {
638 return l->literal();
639 }
640 }
641 }
642 // If the bucket size is too deep check if this hash code is insufficient.
643 if (count >= BasicHashtable<mtSymbol>::rehash_count && !needs_rehashing()) {
644 _needs_rehashing = check_rehash_table(count);
645 }
646 return NULL;
647 }
650 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
651 int len, unsigned int hashValue_arg, TRAPS) {
653 assert(java_lang_String::equals(string(), name, len),
654 "string must be properly initialized");
655 // Cannot hit a safepoint in this function because the "this" pointer can move.
656 No_Safepoint_Verifier nsv;
658 // Check if the symbol table has been rehashed, if so, need to recalculate
659 // the hash value and index before second lookup.
660 unsigned int hashValue;
661 int index;
662 if (use_alternate_hashcode()) {
663 hashValue = hash_string(name, len);
664 index = hash_to_index(hashValue);
665 } else {
666 hashValue = hashValue_arg;
667 index = index_arg;
668 }
670 // Since look-up was done lock-free, we need to check if another
671 // thread beat us in the race to insert the symbol.
673 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
674 if (test != NULL) {
675 // Entry already added
676 return test;
677 }
679 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
680 add_entry(index, entry);
681 return string();
682 }
685 oop StringTable::lookup(Symbol* symbol) {
686 ResourceMark rm;
687 int length;
688 jchar* chars = symbol->as_unicode(length);
689 unsigned int hashValue = hash_string(chars, length);
690 int index = the_table()->hash_to_index(hashValue);
691 return the_table()->lookup(index, chars, length, hashValue);
692 }
695 oop StringTable::intern(Handle string_or_null, jchar* name,
696 int len, TRAPS) {
697 unsigned int hashValue = hash_string(name, len);
698 int index = the_table()->hash_to_index(hashValue);
699 oop found_string = the_table()->lookup(index, name, len, hashValue);
701 // Found
702 if (found_string != NULL) return found_string;
704 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
705 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
706 "proposed name of symbol must be stable");
708 Handle string;
709 // try to reuse the string if possible
710 if (!string_or_null.is_null() && (!JavaObjectsInPerm || string_or_null()->is_perm())) {
711 string = string_or_null;
712 } else {
713 string = java_lang_String::create_tenured_from_unicode(name, len, CHECK_NULL);
714 }
716 // Grab the StringTable_lock before getting the_table() because it could
717 // change at safepoint.
718 MutexLocker ml(StringTable_lock, THREAD);
720 // Otherwise, add to symbol to table
721 return the_table()->basic_add(index, string, name, len,
722 hashValue, CHECK_NULL);
723 }
725 oop StringTable::intern(Symbol* symbol, TRAPS) {
726 if (symbol == NULL) return NULL;
727 ResourceMark rm(THREAD);
728 int length;
729 jchar* chars = symbol->as_unicode(length);
730 Handle string;
731 oop result = intern(string, chars, length, CHECK_NULL);
732 return result;
733 }
736 oop StringTable::intern(oop string, TRAPS)
737 {
738 if (string == NULL) return NULL;
739 ResourceMark rm(THREAD);
740 int length;
741 Handle h_string (THREAD, string);
742 jchar* chars = java_lang_String::as_unicode_string(string, length);
743 oop result = intern(h_string, chars, length, CHECK_NULL);
744 return result;
745 }
748 oop StringTable::intern(const char* utf8_string, TRAPS) {
749 if (utf8_string == NULL) return NULL;
750 ResourceMark rm(THREAD);
751 int length = UTF8::unicode_length(utf8_string);
752 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
753 UTF8::convert_to_unicode(utf8_string, chars, length);
754 Handle string;
755 oop result = intern(string, chars, length, CHECK_NULL);
756 return result;
757 }
759 void StringTable::unlink(BoolObjectClosure* is_alive) {
760 // Readers of the table are unlocked, so we should only be removing
761 // entries at a safepoint.
762 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
763 for (int i = 0; i < the_table()->table_size(); ++i) {
764 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
765 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
766 while (entry != NULL) {
767 // Shared entries are normally at the end of the bucket and if we run into
768 // a shared entry, then there is nothing more to remove. However, if we
769 // have rehashed the table, then the shared entries are no longer at the
770 // end of the bucket.
771 if (entry->is_shared() && !use_alternate_hashcode()) {
772 break;
773 }
774 assert(entry->literal() != NULL, "just checking");
775 if (entry->is_shared() || is_alive->do_object_b(entry->literal())) {
776 p = entry->next_addr();
777 } else {
778 *p = entry->next();
779 the_table()->free_entry(entry);
780 }
781 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
782 }
783 }
784 }
786 void StringTable::oops_do(OopClosure* f) {
787 for (int i = 0; i < the_table()->table_size(); ++i) {
788 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
789 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
790 while (entry != NULL) {
791 f->do_oop((oop*)entry->literal_addr());
793 // Did the closure remove the literal from the table?
794 if (entry->literal() == NULL) {
795 assert(!entry->is_shared(), "immutable hashtable entry?");
796 *p = entry->next();
797 the_table()->free_entry(entry);
798 } else {
799 p = entry->next_addr();
800 }
801 entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
802 }
803 }
804 }
806 void StringTable::verify() {
807 for (int i = 0; i < the_table()->table_size(); ++i) {
808 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
809 for ( ; p != NULL; p = p->next()) {
810 oop s = p->literal();
811 guarantee(s != NULL, "interned string is NULL");
812 guarantee(s->is_perm() || !JavaObjectsInPerm, "interned string not in permspace");
813 unsigned int h = java_lang_String::hash_string(s);
814 guarantee(p->hash() == h, "broken hash in string table entry");
815 guarantee(the_table()->hash_to_index(h) == i,
816 "wrong index in string table");
817 }
818 }
819 }
821 void StringTable::dump(outputStream* st) {
822 NumberSeq summary;
823 for (int i = 0; i < the_table()->table_size(); ++i) {
824 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
825 int count = 0;
826 for ( ; p != NULL; p = p->next()) {
827 count++;
828 }
829 summary.add((double)count);
830 }
831 st->print_cr("StringTable statistics:");
832 st->print_cr("Number of buckets : %7d", summary.num());
833 st->print_cr("Average bucket size : %7.0f", summary.avg());
834 st->print_cr("Variance of bucket size : %7.0f", summary.variance());
835 st->print_cr("Std. dev. of bucket size: %7.0f", summary.sd());
836 st->print_cr("Maximum bucket size : %7.0f", summary.maximum());
837 }
840 unsigned int StringTable::new_hash(oop string) {
841 ResourceMark rm;
842 int length;
843 jchar* chars = java_lang_String::as_unicode_string(string, length);
844 // Use alternate hashing algorithm on the string
845 return AltHashing::murmur3_32(seed(), chars, length);
846 }
848 // Create a new table and using alternate hash code, populate the new table
849 // with the existing strings. Set flag to use the alternate hash code afterwards.
850 void StringTable::rehash_table() {
851 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
852 // This should never happen with -Xshare:dump but it might in testing mode.
853 if (DumpSharedSpaces) return;
854 StringTable* new_table = new StringTable();
856 // Initialize new global seed for hashing.
857 _seed = AltHashing::compute_seed();
858 assert(seed() != 0, "shouldn't be zero");
860 // Rehash the table
861 the_table()->move_to(new_table);
863 // Delete the table and buckets (entries are reused in new table).
864 delete _the_table;
865 // Don't check if we need rehashing until the table gets unbalanced again.
866 // Then rehash with a new global seed.
867 _needs_rehashing = false;
868 _the_table = new_table;
869 }