1 /*
2 * Copyright (c) 1997, 2020, 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/compactHashtable.hpp"
28 #include "classfile/javaClasses.hpp"
29 #include "classfile/symbolTable.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/dynamicArchive.hpp"
32 #include "memory/metaspaceClosure.hpp"
33 #include "memory/metaspaceShared.hpp"
34 #include "memory/resourceArea.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/interfaceSupport.inline.hpp"
38 #include "runtime/timerTrace.hpp"
39 #include "services/diagnosticCommand.hpp"
40 #include "utilities/concurrentHashTable.inline.hpp"
41 #include "utilities/concurrentHashTableTasks.inline.hpp"
42 #include "utilities/utf8.hpp"
43
44 // We used to not resize at all, so let's be conservative
45 // and not set it too short before we decide to resize,
46 // to match previous startup behavior
47 const double PREF_AVG_LIST_LEN = 8.0;
48 // 2^24 is max size, like StringTable.
49 const size_t END_SIZE = 24;
50 // If a chain gets to 100 something might be wrong
51 const size_t REHASH_LEN = 100;
52
53 const size_t ON_STACK_BUFFER_LENGTH = 128;
54
55 // --------------------------------------------------------------------------
56
57 inline bool symbol_equals_compact_hashtable_entry(Symbol* value, const char* key, int len) {
58 if (value->equals(key, len)) {
59 assert(value->is_permanent(), "must be shared");
60 return true;
61 } else {
62 return false;
63 }
64 }
65
66 static OffsetCompactHashtable<
67 const char*, Symbol*,
68 symbol_equals_compact_hashtable_entry
69 > _shared_table;
70
71 static OffsetCompactHashtable<
72 const char*, Symbol*,
73 symbol_equals_compact_hashtable_entry
74 > _dynamic_shared_table;
75
76 // --------------------------------------------------------------------------
77
78 typedef ConcurrentHashTable<SymbolTableConfig, mtSymbol> SymbolTableHash;
79 static SymbolTableHash* _local_table = NULL;
80
81 volatile bool SymbolTable::_has_work = 0;
82 volatile bool SymbolTable::_needs_rehashing = false;
83
84 // For statistics
85 static size_t _symbols_removed = 0;
86 static size_t _symbols_counted = 0;
87 static size_t _current_size = 0;
88
89 static volatile size_t _items_count = 0;
90 static volatile bool _has_items_to_clean = false;
91
92
93 static volatile bool _alt_hash = false;
94 static volatile bool _lookup_shared_first = false;
95
96 // Static arena for symbols that are not deallocated
97 Arena* SymbolTable::_arena = NULL;
98
99 static juint murmur_seed = 0;
100
101 static inline void log_trace_symboltable_helper(Symbol* sym, const char* msg) {
102 #ifndef PRODUCT
103 ResourceMark rm;
104 log_trace(symboltable)("%s [%s]", msg, sym->as_quoted_ascii());
105 #endif // PRODUCT
106 }
107
108 // Pick hashing algorithm.
109 static uintx hash_symbol(const char* s, int len, bool useAlt) {
110 return useAlt ?
111 AltHashing::murmur3_32(murmur_seed, (const jbyte*)s, len) :
112 java_lang_String::hash_code((const jbyte*)s, len);
113 }
114
115 #if INCLUDE_CDS
116 static uintx hash_shared_symbol(const char* s, int len) {
117 return java_lang_String::hash_code((const jbyte*)s, len);
118 }
119 #endif
120
121 class SymbolTableConfig : public AllStatic {
122 private:
123 public:
124 typedef Symbol* Value; // value of the Node in the hashtable
125
126 static uintx get_hash(Value const& value, bool* is_dead) {
127 *is_dead = (value->refcount() == 0);
128 if (*is_dead) {
129 return 0;
130 } else {
131 return hash_symbol((const char*)value->bytes(), value->utf8_length(), _alt_hash);
132 }
133 }
134 // We use default allocation/deallocation but counted
135 static void* allocate_node(size_t size, Value const& value) {
136 SymbolTable::item_added();
137 return AllocateHeap(size, mtSymbol);
138 }
139 static void free_node(void* memory, Value const& value) {
140 // We get here because #1 some threads lost a race to insert a newly created Symbol
141 // or #2 we're cleaning up unused symbol.
142 // If #1, then the symbol can be either permanent,
143 // or regular newly created one (refcount==1)
144 // If #2, then the symbol is dead (refcount==0)
145 assert(value->is_permanent() || (value->refcount() == 1) || (value->refcount() == 0),
146 "refcount %d", value->refcount());
147 if (value->refcount() == 1) {
148 value->decrement_refcount();
149 assert(value->refcount() == 0, "expected dead symbol");
150 }
151 SymbolTable::delete_symbol(value);
152 FreeHeap(memory);
153 SymbolTable::item_removed();
154 }
155 };
156
157 static size_t ceil_log2(size_t value) {
158 size_t ret;
159 for (ret = 1; ((size_t)1 << ret) < value; ++ret);
160 return ret;
161 }
162
163 void SymbolTable::create_table () {
164 size_t start_size_log_2 = ceil_log2(SymbolTableSize);
165 _current_size = ((size_t)1) << start_size_log_2;
166 log_trace(symboltable)("Start size: " SIZE_FORMAT " (" SIZE_FORMAT ")",
167 _current_size, start_size_log_2);
168 _local_table = new SymbolTableHash(start_size_log_2, END_SIZE, REHASH_LEN);
169
170 // Initialize the arena for global symbols, size passed in depends on CDS.
171 if (symbol_alloc_arena_size == 0) {
172 _arena = new (mtSymbol) Arena(mtSymbol);
173 } else {
174 _arena = new (mtSymbol) Arena(mtSymbol, symbol_alloc_arena_size);
175 }
176 }
177
178 void SymbolTable::delete_symbol(Symbol* sym) {
179 if (Arguments::is_dumping_archive()) {
180 // Do not delete symbols as we may be in the middle of preparing the
181 // symbols for dumping.
182 return;
183 }
184 if (sym->is_permanent()) {
185 MutexLocker ml(SymbolArena_lock, Mutex::_no_safepoint_check_flag); // Protect arena
186 // Deleting permanent symbol should not occur very often (insert race condition),
187 // so log it.
188 log_trace_symboltable_helper(sym, "Freeing permanent symbol");
189 if (!arena()->Afree(sym, sym->size())) {
190 log_trace_symboltable_helper(sym, "Leaked permanent symbol");
191 }
192 } else {
193 delete sym;
194 }
195 }
196
197 void SymbolTable::reset_has_items_to_clean() { Atomic::store(&_has_items_to_clean, false); }
198 void SymbolTable::mark_has_items_to_clean() { Atomic::store(&_has_items_to_clean, true); }
199 bool SymbolTable::has_items_to_clean() { return Atomic::load(&_has_items_to_clean); }
200
201 void SymbolTable::item_added() {
202 Atomic::inc(&_items_count);
203 }
204
205 void SymbolTable::item_removed() {
206 Atomic::inc(&(_symbols_removed));
207 Atomic::dec(&_items_count);
208 }
209
210 double SymbolTable::get_load_factor() {
211 return (double)_items_count/_current_size;
212 }
213
214 size_t SymbolTable::table_size() {
215 return ((size_t)1) << _local_table->get_size_log2(Thread::current());
216 }
217
218 void SymbolTable::trigger_cleanup() {
219 MutexLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
220 _has_work = true;
221 Service_lock->notify_all();
222 }
223
224 Symbol* SymbolTable::allocate_symbol(const char* name, int len, bool c_heap) {
225 assert (len <= Symbol::max_length(), "should be checked by caller");
226
227 Symbol* sym;
228 if (Arguments::is_dumping_archive()) {
229 // Need to make all symbols permanent -- or else some symbols may be GC'ed
230 // during the archive dumping code that's executed outside of a safepoint.
231 c_heap = false;
232 }
233 if (c_heap) {
234 // refcount starts as 1
235 sym = new (len) Symbol((const u1*)name, len, 1);
236 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
237 } else if (DumpSharedSpaces) {
238 // See comments inside Symbol::operator new(size_t, int)
239 sym = new (len) Symbol((const u1*)name, len, PERM_REFCOUNT);
240 assert(sym != NULL, "new should call vm_exit_out_of_memory if failed to allocate symbol during DumpSharedSpaces");
241 } else {
242 // Allocate to global arena
243 MutexLocker ml(SymbolArena_lock, Mutex::_no_safepoint_check_flag); // Protect arena
244 sym = new (len, arena()) Symbol((const u1*)name, len, PERM_REFCOUNT);
245 }
246 return sym;
247 }
248
249 class SymbolsDo : StackObj {
250 SymbolClosure *_cl;
251 public:
252 SymbolsDo(SymbolClosure *cl) : _cl(cl) {}
253 bool operator()(Symbol** value) {
254 assert(value != NULL, "expected valid value");
255 assert(*value != NULL, "value should point to a symbol");
256 _cl->do_symbol(value);
257 return true;
258 };
259 };
260
261 class SharedSymbolIterator {
262 SymbolClosure* _symbol_closure;
263 public:
264 SharedSymbolIterator(SymbolClosure* f) : _symbol_closure(f) {}
265 void do_value(Symbol* symbol) {
266 _symbol_closure->do_symbol(&symbol);
267 }
268 };
269
270 // Call function for all symbols in the symbol table.
271 void SymbolTable::symbols_do(SymbolClosure *cl) {
272 // all symbols from shared table
273 SharedSymbolIterator iter(cl);
274 _shared_table.iterate(&iter);
275 _dynamic_shared_table.iterate(&iter);
276
277 // all symbols from the dynamic table
278 SymbolsDo sd(cl);
279 if (!_local_table->try_scan(Thread::current(), sd)) {
280 log_info(symboltable)("symbols_do unavailable at this moment");
281 }
282 }
283
284 class MetaspacePointersDo : StackObj {
285 MetaspaceClosure *_it;
286 public:
287 MetaspacePointersDo(MetaspaceClosure *it) : _it(it) {}
288 bool operator()(Symbol** value) {
289 assert(value != NULL, "expected valid value");
290 assert(*value != NULL, "value should point to a symbol");
291 _it->push(value);
292 return true;
293 };
294 };
295
296 void SymbolTable::metaspace_pointers_do(MetaspaceClosure* it) {
297 Arguments::assert_is_dumping_archive();
298 MetaspacePointersDo mpd(it);
299 _local_table->do_safepoint_scan(mpd);
300 }
301
302 Symbol* SymbolTable::lookup_dynamic(const char* name,
303 int len, unsigned int hash) {
304 Symbol* sym = do_lookup(name, len, hash);
305 assert((sym == NULL) || sym->refcount() != 0, "refcount must not be zero");
306 return sym;
307 }
308
309 #if INCLUDE_CDS
310 Symbol* SymbolTable::lookup_shared(const char* name,
311 int len, unsigned int hash) {
312 Symbol* sym = NULL;
313 if (!_shared_table.empty()) {
314 if (_alt_hash) {
315 // hash_code parameter may use alternate hashing algorithm but the shared table
316 // always uses the same original hash code.
317 hash = hash_shared_symbol(name, len);
318 }
319 sym = _shared_table.lookup(name, hash, len);
320 if (sym == NULL && DynamicArchive::is_mapped()) {
321 sym = _dynamic_shared_table.lookup(name, hash, len);
322 }
323 }
324 return sym;
325 }
326 #endif
327
328 Symbol* SymbolTable::lookup_common(const char* name,
329 int len, unsigned int hash) {
330 Symbol* sym;
331 if (_lookup_shared_first) {
332 sym = lookup_shared(name, len, hash);
333 if (sym == NULL) {
334 _lookup_shared_first = false;
335 sym = lookup_dynamic(name, len, hash);
336 }
337 } else {
338 sym = lookup_dynamic(name, len, hash);
339 if (sym == NULL) {
340 sym = lookup_shared(name, len, hash);
341 if (sym != NULL) {
342 _lookup_shared_first = true;
343 }
344 }
345 }
346 return sym;
347 }
348
349 Symbol* SymbolTable::new_symbol(const char* name, int len) {
350 unsigned int hash = hash_symbol(name, len, _alt_hash);
351 Symbol* sym = lookup_common(name, len, hash);
352 if (sym == NULL) {
353 sym = do_add_if_needed(name, len, hash, true);
354 }
355 assert(sym->refcount() != 0, "lookup should have incremented the count");
356 assert(sym->equals(name, len), "symbol must be properly initialized");
357 return sym;
358 }
359
360 Symbol* SymbolTable::new_symbol(const Symbol* sym, int begin, int end) {
361 assert(begin <= end && end <= sym->utf8_length(), "just checking");
362 assert(sym->refcount() != 0, "require a valid symbol");
363 const char* name = (const char*)sym->base() + begin;
364 int len = end - begin;
365 unsigned int hash = hash_symbol(name, len, _alt_hash);
366 Symbol* found = lookup_common(name, len, hash);
367 if (found == NULL) {
368 found = do_add_if_needed(name, len, hash, true);
369 }
370 return found;
371 }
372
373 class SymbolTableLookup : StackObj {
374 private:
375 Thread* _thread;
376 uintx _hash;
377 int _len;
378 const char* _str;
379 public:
380 SymbolTableLookup(const char* key, int len, uintx hash)
381 : _hash(hash), _len(len), _str(key) {}
382 uintx get_hash() const {
383 return _hash;
384 }
385 bool equals(Symbol** value, bool* is_dead) {
386 assert(value != NULL, "expected valid value");
387 assert(*value != NULL, "value should point to a symbol");
388 Symbol *sym = *value;
389 if (sym->equals(_str, _len)) {
390 if (sym->try_increment_refcount()) {
391 // something is referencing this symbol now.
392 return true;
393 } else {
394 assert(sym->refcount() == 0, "expected dead symbol");
395 *is_dead = true;
396 return false;
397 }
398 } else {
399 *is_dead = (sym->refcount() == 0);
400 return false;
401 }
402 }
403 };
404
405 class SymbolTableGet : public StackObj {
406 Symbol* _return;
407 public:
408 SymbolTableGet() : _return(NULL) {}
409 void operator()(Symbol** value) {
410 assert(value != NULL, "expected valid value");
411 assert(*value != NULL, "value should point to a symbol");
412 _return = *value;
413 }
414 Symbol* get_res_sym() const {
415 return _return;
416 }
417 };
418
419 Symbol* SymbolTable::do_lookup(const char* name, int len, uintx hash) {
420 Thread* thread = Thread::current();
421 SymbolTableLookup lookup(name, len, hash);
422 SymbolTableGet stg;
423 bool rehash_warning = false;
424 _local_table->get(thread, lookup, stg, &rehash_warning);
425 update_needs_rehash(rehash_warning);
426 Symbol* sym = stg.get_res_sym();
427 assert((sym == NULL) || sym->refcount() != 0, "found dead symbol");
428 return sym;
429 }
430
431 Symbol* SymbolTable::lookup_only(const char* name, int len, unsigned int& hash) {
432 hash = hash_symbol(name, len, _alt_hash);
433 return lookup_common(name, len, hash);
434 }
435
436 // Suggestion: Push unicode-based lookup all the way into the hashing
437 // and probing logic, so there is no need for convert_to_utf8 until
438 // an actual new Symbol* is created.
439 Symbol* SymbolTable::new_symbol(const jchar* name, int utf16_length) {
440 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
441 char stack_buf[ON_STACK_BUFFER_LENGTH];
442 if (utf8_length < (int) sizeof(stack_buf)) {
443 char* chars = stack_buf;
444 UNICODE::convert_to_utf8(name, utf16_length, chars);
445 return new_symbol(chars, utf8_length);
446 } else {
447 ResourceMark rm;
448 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
449 UNICODE::convert_to_utf8(name, utf16_length, chars);
450 return new_symbol(chars, utf8_length);
451 }
452 }
453
454 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
455 unsigned int& hash) {
456 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
457 char stack_buf[ON_STACK_BUFFER_LENGTH];
458 if (utf8_length < (int) sizeof(stack_buf)) {
459 char* chars = stack_buf;
460 UNICODE::convert_to_utf8(name, utf16_length, chars);
461 return lookup_only(chars, utf8_length, hash);
462 } else {
463 ResourceMark rm;
464 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
465 UNICODE::convert_to_utf8(name, utf16_length, chars);
466 return lookup_only(chars, utf8_length, hash);
467 }
468 }
469
470 void SymbolTable::new_symbols(ClassLoaderData* loader_data, const constantPoolHandle& cp,
471 int names_count, const char** names, int* lengths,
472 int* cp_indices, unsigned int* hashValues) {
473 // Note that c_heap will be true for non-strong hidden classes and unsafe anonymous classes
474 // even if their loader is the boot loader because they will have a different cld.
475 bool c_heap = !loader_data->is_the_null_class_loader_data();
476 for (int i = 0; i < names_count; i++) {
477 const char *name = names[i];
478 int len = lengths[i];
479 unsigned int hash = hashValues[i];
480 assert(lookup_shared(name, len, hash) == NULL, "must have checked already");
481 Symbol* sym = do_add_if_needed(name, len, hash, c_heap);
482 assert(sym->refcount() != 0, "lookup should have incremented the count");
483 cp->symbol_at_put(cp_indices[i], sym);
484 }
485 }
486
487 Symbol* SymbolTable::do_add_if_needed(const char* name, int len, uintx hash, bool heap) {
488 SymbolTableLookup lookup(name, len, hash);
489 SymbolTableGet stg;
490 bool clean_hint = false;
491 bool rehash_warning = false;
492 Symbol* sym = NULL;
493 Thread* THREAD = Thread::current();
494
495 do {
496 // Callers have looked up the symbol once, insert the symbol.
497 sym = allocate_symbol(name, len, heap);
498 if (_local_table->insert(THREAD, lookup, sym, &rehash_warning, &clean_hint)) {
499 break;
500 }
501 // In case another thread did a concurrent add, return value already in the table.
502 // This could fail if the symbol got deleted concurrently, so loop back until success.
503 if (_local_table->get(THREAD, lookup, stg, &rehash_warning)) {
504 sym = stg.get_res_sym();
505 break;
506 }
507 } while(true);
508
509 update_needs_rehash(rehash_warning);
510
511 if (clean_hint) {
512 mark_has_items_to_clean();
513 check_concurrent_work();
514 }
515
516 assert((sym == NULL) || sym->refcount() != 0, "found dead symbol");
517 return sym;
518 }
519
520 Symbol* SymbolTable::new_permanent_symbol(const char* name) {
521 unsigned int hash = 0;
522 int len = (int)strlen(name);
523 Symbol* sym = SymbolTable::lookup_only(name, len, hash);
524 if (sym == NULL) {
525 sym = do_add_if_needed(name, len, hash, false);
526 }
527 if (!sym->is_permanent()) {
528 sym->make_permanent();
529 log_trace_symboltable_helper(sym, "Asked for a permanent symbol, but got a regular one");
530 }
531 return sym;
532 }
533
534 struct SizeFunc : StackObj {
535 size_t operator()(Symbol** value) {
536 assert(value != NULL, "expected valid value");
537 assert(*value != NULL, "value should point to a symbol");
538 return (*value)->size() * HeapWordSize;
539 };
540 };
541
542 TableStatistics SymbolTable::get_table_statistics() {
543 static TableStatistics ts;
544 SizeFunc sz;
545 ts = _local_table->statistics_get(Thread::current(), sz, ts);
546 return ts;
547 }
548
549 void SymbolTable::print_table_statistics(outputStream* st,
550 const char* table_name) {
551 SizeFunc sz;
552 _local_table->statistics_to(Thread::current(), sz, st, table_name);
553 }
554
555 // Verification
556 class VerifySymbols : StackObj {
557 public:
558 bool operator()(Symbol** value) {
559 guarantee(value != NULL, "expected valid value");
560 guarantee(*value != NULL, "value should point to a symbol");
561 Symbol* sym = *value;
562 guarantee(sym->equals((const char*)sym->bytes(), sym->utf8_length()),
563 "symbol must be internally consistent");
564 return true;
565 };
566 };
567
568 void SymbolTable::verify() {
569 Thread* thr = Thread::current();
570 VerifySymbols vs;
571 if (!_local_table->try_scan(thr, vs)) {
572 log_info(symboltable)("verify unavailable at this moment");
573 }
574 }
575
576 // Dumping
577 class DumpSymbol : StackObj {
578 Thread* _thr;
579 outputStream* _st;
580 public:
581 DumpSymbol(Thread* thr, outputStream* st) : _thr(thr), _st(st) {}
582 bool operator()(Symbol** value) {
583 assert(value != NULL, "expected valid value");
584 assert(*value != NULL, "value should point to a symbol");
585 Symbol* sym = *value;
586 const char* utf8_string = (const char*)sym->bytes();
587 int utf8_length = sym->utf8_length();
588 _st->print("%d %d: ", utf8_length, sym->refcount());
589 HashtableTextDump::put_utf8(_st, utf8_string, utf8_length);
590 _st->cr();
591 return true;
592 };
593 };
594
595 void SymbolTable::dump(outputStream* st, bool verbose) {
596 if (!verbose) {
597 print_table_statistics(st, "SymbolTable");
598 } else {
599 Thread* thr = Thread::current();
600 ResourceMark rm(thr);
601 st->print_cr("VERSION: 1.1");
602 DumpSymbol ds(thr, st);
603 if (!_local_table->try_scan(thr, ds)) {
604 log_info(symboltable)("dump unavailable at this moment");
605 }
606 }
607 }
608
609 #if INCLUDE_CDS
610 struct CopyToArchive : StackObj {
611 CompactHashtableWriter* _writer;
612 CopyToArchive(CompactHashtableWriter* writer) : _writer(writer) {}
613 bool operator()(Symbol** value) {
614 assert(value != NULL, "expected valid value");
615 assert(*value != NULL, "value should point to a symbol");
616 Symbol* sym = *value;
617 unsigned int fixed_hash = hash_shared_symbol((const char*)sym->bytes(), sym->utf8_length());
618 assert(fixed_hash == hash_symbol((const char*)sym->bytes(), sym->utf8_length(), false),
619 "must not rehash during dumping");
620 if (DynamicDumpSharedSpaces) {
621 sym = DynamicArchive::original_to_target(sym);
622 }
623 _writer->add(fixed_hash, MetaspaceShared::object_delta_u4(sym));
624 return true;
625 }
626 };
627
628 void SymbolTable::copy_shared_symbol_table(CompactHashtableWriter* writer) {
629 CopyToArchive copy(writer);
630 _local_table->do_safepoint_scan(copy);
631 }
632
633 size_t SymbolTable::estimate_size_for_archive() {
634 return CompactHashtableWriter::estimate_size(int(_items_count));
635 }
636
637 void SymbolTable::write_to_archive(bool is_static_archive) {
638 CompactHashtableWriter writer(int(_items_count),
639 &MetaspaceShared::stats()->symbol);
640 copy_shared_symbol_table(&writer);
641 if (is_static_archive) {
642 _shared_table.reset();
643 writer.dump(&_shared_table, "symbol");
644
645 // Verify table is correct
646 Symbol* sym = vmSymbols::java_lang_Object();
647 const char* name = (const char*)sym->bytes();
648 int len = sym->utf8_length();
649 unsigned int hash = hash_symbol(name, len, _alt_hash);
650 assert(sym == _shared_table.lookup(name, hash, len), "sanity");
651 } else {
652 _dynamic_shared_table.reset();
653 writer.dump(&_dynamic_shared_table, "symbol");
654 }
655 }
656
657 void SymbolTable::serialize_shared_table_header(SerializeClosure* soc,
658 bool is_static_archive) {
659 OffsetCompactHashtable<const char*, Symbol*, symbol_equals_compact_hashtable_entry> * table;
660 if (is_static_archive) {
661 table = &_shared_table;
662 } else {
663 table = &_dynamic_shared_table;
664 }
665 table->serialize_header(soc);
666 if (soc->writing()) {
667 // Sanity. Make sure we don't use the shared table at dump time
668 table->reset();
669 }
670 }
671 #endif //INCLUDE_CDS
672
673 // Concurrent work
674 void SymbolTable::grow(JavaThread* jt) {
675 SymbolTableHash::GrowTask gt(_local_table);
676 if (!gt.prepare(jt)) {
677 return;
678 }
679 log_trace(symboltable)("Started to grow");
680 {
681 TraceTime timer("Grow", TRACETIME_LOG(Debug, symboltable, perf));
682 while (gt.do_task(jt)) {
683 gt.pause(jt);
684 {
685 ThreadBlockInVM tbivm(jt);
686 }
687 gt.cont(jt);
688 }
689 }
690 gt.done(jt);
691 _current_size = table_size();
692 log_debug(symboltable)("Grown to size:" SIZE_FORMAT, _current_size);
693 }
694
695 struct SymbolTableDoDelete : StackObj {
696 size_t _deleted;
697 SymbolTableDoDelete() : _deleted(0) {}
698 void operator()(Symbol** value) {
699 assert(value != NULL, "expected valid value");
700 assert(*value != NULL, "value should point to a symbol");
701 Symbol *sym = *value;
702 assert(sym->refcount() == 0, "refcount");
703 _deleted++;
704 }
705 };
706
707 struct SymbolTableDeleteCheck : StackObj {
708 size_t _processed;
709 SymbolTableDeleteCheck() : _processed(0) {}
710 bool operator()(Symbol** value) {
711 assert(value != NULL, "expected valid value");
712 assert(*value != NULL, "value should point to a symbol");
713 _processed++;
714 Symbol *sym = *value;
715 return (sym->refcount() == 0);
716 }
717 };
718
719 void SymbolTable::clean_dead_entries(JavaThread* jt) {
720 SymbolTableHash::BulkDeleteTask bdt(_local_table);
721 if (!bdt.prepare(jt)) {
722 return;
723 }
724
725 SymbolTableDeleteCheck stdc;
726 SymbolTableDoDelete stdd;
727 {
728 TraceTime timer("Clean", TRACETIME_LOG(Debug, symboltable, perf));
729 while (bdt.do_task(jt, stdc, stdd)) {
730 bdt.pause(jt);
731 {
732 ThreadBlockInVM tbivm(jt);
733 }
734 bdt.cont(jt);
735 }
736 reset_has_items_to_clean();
737 bdt.done(jt);
738 }
739
740 Atomic::add(&_symbols_counted, stdc._processed);
741
742 log_debug(symboltable)("Cleaned " SIZE_FORMAT " of " SIZE_FORMAT,
743 stdd._deleted, stdc._processed);
744 }
745
746 void SymbolTable::check_concurrent_work() {
747 if (_has_work) {
748 return;
749 }
750 // We should clean/resize if we have
751 // more items than preferred load factor or
752 // more dead items than water mark.
753 if (has_items_to_clean() || (get_load_factor() > PREF_AVG_LIST_LEN)) {
754 log_debug(symboltable)("Concurrent work triggered, load factor: %f, items to clean: %s",
755 get_load_factor(), has_items_to_clean() ? "true" : "false");
756 trigger_cleanup();
757 }
758 }
759
760 void SymbolTable::do_concurrent_work(JavaThread* jt) {
761 double load_factor = get_load_factor();
762 log_debug(symboltable, perf)("Concurrent work, live factor: %g", load_factor);
763 // We prefer growing, since that also removes dead items
764 if (load_factor > PREF_AVG_LIST_LEN && !_local_table->is_max_size_reached()) {
765 grow(jt);
766 } else {
767 clean_dead_entries(jt);
768 }
769 _has_work = false;
770 }
771
772 // Rehash
773 bool SymbolTable::do_rehash() {
774 if (!_local_table->is_safepoint_safe()) {
775 return false;
776 }
777
778 // We use current size
779 size_t new_size = _local_table->get_size_log2(Thread::current());
780 SymbolTableHash* new_table = new SymbolTableHash(new_size, END_SIZE, REHASH_LEN);
781 // Use alt hash from now on
782 _alt_hash = true;
783 if (!_local_table->try_move_nodes_to(Thread::current(), new_table)) {
784 _alt_hash = false;
785 delete new_table;
786 return false;
787 }
788
789 // free old table
790 delete _local_table;
791 _local_table = new_table;
792
793 return true;
794 }
795
796 void SymbolTable::rehash_table() {
797 static bool rehashed = false;
798 log_debug(symboltable)("Table imbalanced, rehashing called.");
799
800 // Grow instead of rehash.
801 if (get_load_factor() > PREF_AVG_LIST_LEN &&
802 !_local_table->is_max_size_reached()) {
803 log_debug(symboltable)("Choosing growing over rehashing.");
804 trigger_cleanup();
805 _needs_rehashing = false;
806 return;
807 }
808
809 // Already rehashed.
810 if (rehashed) {
811 log_warning(symboltable)("Rehashing already done, still long lists.");
812 trigger_cleanup();
813 _needs_rehashing = false;
814 return;
815 }
816
817 murmur_seed = AltHashing::compute_seed();
818
819 if (do_rehash()) {
820 rehashed = true;
821 } else {
822 log_info(symboltable)("Resizes in progress rehashing skipped.");
823 }
824
825 _needs_rehashing = false;
826 }
827
828 //---------------------------------------------------------------------------
829 // Non-product code
830
831 #ifndef PRODUCT
832
833 class HistogramIterator : StackObj {
834 public:
835 static const size_t results_length = 100;
836 size_t counts[results_length];
837 size_t sizes[results_length];
838 size_t total_size;
839 size_t total_count;
840 size_t total_length;
841 size_t max_length;
842 size_t out_of_range_count;
843 size_t out_of_range_size;
844 HistogramIterator() : total_size(0), total_count(0), total_length(0),
845 max_length(0), out_of_range_count(0), out_of_range_size(0) {
846 // initialize results to zero
847 for (size_t i = 0; i < results_length; i++) {
848 counts[i] = 0;
849 sizes[i] = 0;
850 }
851 }
852 bool operator()(Symbol** value) {
853 assert(value != NULL, "expected valid value");
854 assert(*value != NULL, "value should point to a symbol");
855 Symbol* sym = *value;
856 size_t size = sym->size();
857 size_t len = sym->utf8_length();
858 if (len < results_length) {
859 counts[len]++;
860 sizes[len] += size;
861 } else {
862 out_of_range_count++;
863 out_of_range_size += size;
864 }
865 total_count++;
866 total_size += size;
867 total_length += len;
868 max_length = MAX2(max_length, len);
869
870 return true;
871 };
872 };
873
874 void SymbolTable::print_histogram() {
875 HistogramIterator hi;
876 _local_table->do_scan(Thread::current(), hi);
877 tty->print_cr("Symbol Table Histogram:");
878 tty->print_cr(" Total number of symbols " SIZE_FORMAT_W(7), hi.total_count);
879 tty->print_cr(" Total size in memory " SIZE_FORMAT_W(7) "K",
880 (hi.total_size * wordSize) / 1024);
881 tty->print_cr(" Total counted " SIZE_FORMAT_W(7), _symbols_counted);
882 tty->print_cr(" Total removed " SIZE_FORMAT_W(7), _symbols_removed);
883 if (_symbols_counted > 0) {
884 tty->print_cr(" Percent removed %3.2f",
885 ((float)_symbols_removed / _symbols_counted) * 100);
886 }
887 tty->print_cr(" Reference counts " SIZE_FORMAT_W(7), Symbol::_total_count);
888 tty->print_cr(" Symbol arena used " SIZE_FORMAT_W(7) "K", arena()->used() / 1024);
889 tty->print_cr(" Symbol arena size " SIZE_FORMAT_W(7) "K", arena()->size_in_bytes() / 1024);
890 tty->print_cr(" Total symbol length " SIZE_FORMAT_W(7), hi.total_length);
891 tty->print_cr(" Maximum symbol length " SIZE_FORMAT_W(7), hi.max_length);
892 tty->print_cr(" Average symbol length %7.2f", ((float)hi.total_length / hi.total_count));
893 tty->print_cr(" Symbol length histogram:");
894 tty->print_cr(" %6s %10s %10s", "Length", "#Symbols", "Size");
895 for (size_t i = 0; i < hi.results_length; i++) {
896 if (hi.counts[i] > 0) {
897 tty->print_cr(" " SIZE_FORMAT_W(6) " " SIZE_FORMAT_W(10) " " SIZE_FORMAT_W(10) "K",
898 i, hi.counts[i], (hi.sizes[i] * wordSize) / 1024);
899 }
900 }
901 tty->print_cr(" >=" SIZE_FORMAT_W(6) " " SIZE_FORMAT_W(10) " " SIZE_FORMAT_W(10) "K\n",
902 hi.results_length, hi.out_of_range_count, (hi.out_of_range_size*wordSize) / 1024);
903 }
904 #endif // PRODUCT
905
906 // Utility for dumping symbols
907 SymboltableDCmd::SymboltableDCmd(outputStream* output, bool heap) :
908 DCmdWithParser(output, heap),
909 _verbose("-verbose", "Dump the content of each symbol in the table",
910 "BOOLEAN", false, "false") {
911 _dcmdparser.add_dcmd_option(&_verbose);
912 }
913
914 void SymboltableDCmd::execute(DCmdSource source, TRAPS) {
915 VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSymbols,
916 _verbose.value());
917 VMThread::execute(&dumper);
918 }
919
920 int SymboltableDCmd::num_arguments() {
921 ResourceMark rm;
922 SymboltableDCmd* dcmd = new SymboltableDCmd(NULL, false);
923 if (dcmd != NULL) {
924 DCmdMark mark(dcmd);
925 return dcmd->_dcmdparser.num_arguments();
926 } else {
927 return 0;
928 }
929 }