1 /*
2 * Copyright (c) 1997, 2025, 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 "cds/archiveBuilder.hpp"
26 #include "cds/cdsConfig.hpp"
27 #include "cds/dynamicArchive.hpp"
28 #include "classfile/altHashing.hpp"
29 #include "classfile/classLoaderData.hpp"
30 #include "classfile/compactHashtable.hpp"
31 #include "classfile/javaClasses.hpp"
32 #include "classfile/symbolTable.hpp"
33 #include "memory/allocation.inline.hpp"
34 #include "memory/metaspaceClosure.hpp"
35 #include "memory/resourceArea.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/interfaceSupport.inline.hpp"
39 #include "runtime/timerTrace.hpp"
40 #include "runtime/trimNativeHeap.hpp"
41 #include "services/diagnosticCommand.hpp"
42 #include "utilities/concurrentHashTable.inline.hpp"
43 #include "utilities/concurrentHashTableTasks.inline.hpp"
44 #include "utilities/utf8.hpp"
45
46 // We used to not resize at all, so let's be conservative
47 // and not set it too short before we decide to resize,
48 // to match previous startup behavior
49 const double PREF_AVG_LIST_LEN = 8.0;
50 // 2^24 is max size, like StringTable.
51 const size_t END_SIZE = 24;
52 // If a chain gets to 100 something might be wrong
53 const size_t REHASH_LEN = 100;
54
55 const size_t ON_STACK_BUFFER_LENGTH = 128;
56
57 // --------------------------------------------------------------------------
58
59 inline bool symbol_equals_compact_hashtable_entry(Symbol* value, const char* key, int len) {
60 if (value->equals(key, len)) {
61 return true;
62 } else {
63 return false;
64 }
65 }
66
67 static OffsetCompactHashtable<
68 const char*, Symbol*,
69 symbol_equals_compact_hashtable_entry
70 > _shared_table;
71
72 static OffsetCompactHashtable<
73 const char*, Symbol*,
74 symbol_equals_compact_hashtable_entry
75 > _dynamic_shared_table;
76
77 // --------------------------------------------------------------------------
78
79 typedef ConcurrentHashTable<SymbolTableConfig, mtSymbol> SymbolTableHash;
80 static SymbolTableHash* _local_table = nullptr;
81
82 volatile bool SymbolTable::_has_work = 0;
83 volatile bool SymbolTable::_needs_rehashing = false;
84
85 // For statistics
86 static size_t _symbols_removed = 0;
87 static size_t _symbols_counted = 0;
88 static size_t _current_size = 0;
89
90 static volatile size_t _items_count = 0;
91 static volatile bool _has_items_to_clean = false;
92
93
94 static volatile bool _alt_hash = false;
95
96 #ifdef USE_LIBRARY_BASED_TLS_ONLY
97 static volatile bool _lookup_shared_first = false;
98 #else
99 // "_lookup_shared_first" can get highly contended with many cores if multiple threads
100 // are updating "lookup success history" in a global shared variable. If built-in TLS is available, use it.
101 static THREAD_LOCAL bool _lookup_shared_first = false;
102 #endif
103
104 // Static arena for symbols that are not deallocated
105 Arena* SymbolTable::_arena = nullptr;
106
107 static bool _rehashed = false;
108 static uint64_t _alt_hash_seed = 0;
109
110 static inline void log_trace_symboltable_helper(Symbol* sym, const char* msg) {
111 #ifndef PRODUCT
112 ResourceMark rm;
113 log_trace(symboltable)("%s [%s]", msg, sym->as_quoted_ascii());
114 #endif // PRODUCT
115 }
116
117 // Pick hashing algorithm.
118 static unsigned int hash_symbol(const char* s, int len, bool useAlt) {
119 return useAlt ?
120 AltHashing::halfsiphash_32(_alt_hash_seed, (const uint8_t*)s, len) :
121 java_lang_String::hash_code((const jbyte*)s, len);
122 }
123
124 #if INCLUDE_CDS
125 static unsigned int hash_shared_symbol(const char* s, int len) {
126 return java_lang_String::hash_code((const jbyte*)s, len);
127 }
128 #endif
129
130 class SymbolTableConfig : public AllStatic {
131
132 public:
133 typedef Symbol Value; // value of the Node in the hashtable
134
135 static uintx get_hash(Value const& value, bool* is_dead) {
136 *is_dead = (value.refcount() == 0);
137 if (*is_dead) {
138 return 0;
139 } else {
140 return hash_symbol((const char*)value.bytes(), value.utf8_length(), _alt_hash);
141 }
142 }
143 // We use default allocation/deallocation but counted
144 static void* allocate_node(void* context, size_t size, Value const& value) {
145 SymbolTable::item_added();
146 return allocate_node_impl(size, value);
147 }
148 static void free_node(void* context, void* memory, Value & value) {
149 // We get here because #1 some threads lost a race to insert a newly created Symbol
150 // or #2 we're cleaning up unused symbol.
151 // If #1, then the symbol can be either permanent,
152 // or regular newly created one (refcount==1)
153 // If #2, then the symbol is dead (refcount==0)
154 assert(value.is_permanent() || (value.refcount() == 1) || (value.refcount() == 0),
155 "refcount %d", value.refcount());
156 #if INCLUDE_CDS
157 if (CDSConfig::is_dumping_static_archive()) {
158 // We have allocated with MetaspaceShared::symbol_space_alloc(). No deallocation is needed.
159 // Unreferenced Symbols will not be copied into the archive.
160 return;
161 }
162 #endif
163 if (value.refcount() == 1) {
164 value.decrement_refcount();
165 assert(value.refcount() == 0, "expected dead symbol");
166 }
167 if (value.refcount() != PERM_REFCOUNT) {
168 FreeHeap(memory);
169 } else {
170 MutexLocker ml(SymbolArena_lock, Mutex::_no_safepoint_check_flag); // Protect arena
171 // Deleting permanent symbol should not occur very often (insert race condition),
172 // so log it.
173 log_trace_symboltable_helper(&value, "Freeing permanent symbol");
174 size_t alloc_size = SymbolTableHash::get_dynamic_node_size(value.byte_size());
175 if (!SymbolTable::arena()->Afree(memory, alloc_size)) {
176 // Can't access the symbol after Afree, but we just printed it above.
177 NOT_PRODUCT(log_trace(symboltable)(" - Leaked permanent symbol");)
178 }
179 }
180 SymbolTable::item_removed();
181 }
182
183 private:
184 static void* allocate_node_impl(size_t size, Value const& value) {
185 size_t alloc_size = SymbolTableHash::get_dynamic_node_size(value.byte_size());
186 #if INCLUDE_CDS
187 if (CDSConfig::is_dumping_static_archive()) {
188 MutexLocker ml(DumpRegion_lock, Mutex::_no_safepoint_check_flag);
189 // To get deterministic output from -Xshare:dump, we ensure that Symbols are allocated in
190 // increasing addresses. When the symbols are copied into the archive, we preserve their
191 // relative address order (sorted, see ArchiveBuilder::gather_klasses_and_symbols).
192 //
193 // We cannot use arena because arena chunks are allocated by the OS. As a result, for example,
194 // the archived symbol of "java/lang/Object" may sometimes be lower than "java/lang/String", and
195 // sometimes be higher. This would cause non-deterministic contents in the archive.
196 DEBUG_ONLY(static void* last = nullptr);
197 void* p = (void*)MetaspaceShared::symbol_space_alloc(alloc_size);
198 assert(p > last, "must increase monotonically");
199 DEBUG_ONLY(last = p);
200 return p;
201 }
202 #endif
203 if (value.refcount() != PERM_REFCOUNT) {
204 return AllocateHeap(alloc_size, mtSymbol);
205 } else {
206 // Allocate to global arena
207 MutexLocker ml(SymbolArena_lock, Mutex::_no_safepoint_check_flag); // Protect arena
208 return SymbolTable::arena()->Amalloc(alloc_size);
209 }
210 }
211 };
212
213 void SymbolTable::create_table () {
214 size_t start_size_log_2 = log2i_ceil(SymbolTableSize);
215 _current_size = ((size_t)1) << start_size_log_2;
216 log_trace(symboltable)("Start size: %zu (%zu)",
217 _current_size, start_size_log_2);
218 _local_table = new SymbolTableHash(start_size_log_2, END_SIZE, REHASH_LEN, true);
219
220 // Initialize the arena for global symbols, size passed in depends on CDS.
221 if (symbol_alloc_arena_size == 0) {
222 _arena = new (mtSymbol) Arena(mtSymbol);
223 } else {
224 _arena = new (mtSymbol) Arena(mtSymbol, Arena::Tag::tag_other, symbol_alloc_arena_size);
225 }
226 }
227
228 void SymbolTable::reset_has_items_to_clean() { Atomic::store(&_has_items_to_clean, false); }
229 void SymbolTable::mark_has_items_to_clean() { Atomic::store(&_has_items_to_clean, true); }
230 bool SymbolTable::has_items_to_clean() { return Atomic::load(&_has_items_to_clean); }
231
232 void SymbolTable::item_added() {
233 Atomic::inc(&_items_count);
234 }
235
236 void SymbolTable::item_removed() {
237 Atomic::inc(&(_symbols_removed));
238 Atomic::dec(&_items_count);
239 }
240
241 double SymbolTable::get_load_factor() {
242 return (double)_items_count/(double)_current_size;
243 }
244
245 size_t SymbolTable::table_size() {
246 return ((size_t)1) << _local_table->get_size_log2(Thread::current());
247 }
248
249 bool SymbolTable::has_work() { return Atomic::load_acquire(&_has_work); }
250
251 void SymbolTable::trigger_cleanup() {
252 // Avoid churn on ServiceThread
253 if (!has_work()) {
254 MutexLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
255 _has_work = true;
256 Service_lock->notify_all();
257 }
258 }
259
260 class SymbolsDo : StackObj {
261 SymbolClosure *_cl;
262 public:
263 SymbolsDo(SymbolClosure *cl) : _cl(cl) {}
264 bool operator()(Symbol* value) {
265 assert(value != nullptr, "expected valid value");
266 _cl->do_symbol(&value);
267 return true;
268 };
269 };
270
271 class SharedSymbolIterator {
272 SymbolClosure* _symbol_closure;
273 public:
274 SharedSymbolIterator(SymbolClosure* f) : _symbol_closure(f) {}
275 void do_value(Symbol* symbol) {
276 _symbol_closure->do_symbol(&symbol);
277 }
278 };
279
280 // Call function for all symbols in the symbol table.
281 void SymbolTable::symbols_do(SymbolClosure *cl) {
282 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
283 // all symbols from shared table
284 SharedSymbolIterator iter(cl);
285 _shared_table.iterate(&iter);
286 _dynamic_shared_table.iterate(&iter);
287
288 // all symbols from the dynamic table
289 SymbolsDo sd(cl);
290 _local_table->do_safepoint_scan(sd);
291 }
292
293 // Call function for all symbols in shared table. Used by -XX:+PrintSharedArchiveAndExit
294 void SymbolTable::shared_symbols_do(SymbolClosure *cl) {
295 SharedSymbolIterator iter(cl);
296 _shared_table.iterate(&iter);
297 _dynamic_shared_table.iterate(&iter);
298 }
299
300 Symbol* SymbolTable::lookup_dynamic(const char* name,
301 int len, unsigned int hash) {
302 Symbol* sym = do_lookup(name, len, hash);
303 assert((sym == nullptr) || sym->refcount() != 0, "refcount must not be zero");
304 return sym;
305 }
306
307 #if INCLUDE_CDS
308 Symbol* SymbolTable::lookup_shared(const char* name,
309 int len, unsigned int hash) {
310 Symbol* sym = nullptr;
311 if (!_shared_table.empty()) {
312 if (_alt_hash) {
313 // hash_code parameter may use alternate hashing algorithm but the shared table
314 // always uses the same original hash code.
315 hash = hash_shared_symbol(name, len);
316 }
317 sym = _shared_table.lookup(name, hash, len);
318 if (sym == nullptr && DynamicArchive::is_mapped()) {
319 sym = _dynamic_shared_table.lookup(name, hash, len);
320 }
321 }
322 return sym;
323 }
324 #endif
325
326 Symbol* SymbolTable::lookup_common(const char* name,
327 int len, unsigned int hash) {
328 Symbol* sym;
329 if (_lookup_shared_first) {
330 sym = lookup_shared(name, len, hash);
331 if (sym == nullptr) {
332 _lookup_shared_first = false;
333 sym = lookup_dynamic(name, len, hash);
334 }
335 } else {
336 sym = lookup_dynamic(name, len, hash);
337 if (sym == nullptr) {
338 sym = lookup_shared(name, len, hash);
339 if (sym != nullptr) {
340 _lookup_shared_first = true;
341 }
342 }
343 }
344 return sym;
345 }
346
347 // Symbols should represent entities from the constant pool that are
348 // limited to <64K in length, but usage errors creep in allowing Symbols
349 // to be used for arbitrary strings. For debug builds we will assert if
350 // a string is too long, whereas product builds will truncate it.
351 static int check_length(const char* name, int len) {
352 assert(len >= 0, "negative length %d suggests integer overflow in the caller", len);
353 assert(len <= Symbol::max_length(),
354 "String length %d exceeds the maximum Symbol length of %d", len, Symbol::max_length());
355 if (len > Symbol::max_length()) {
356 warning("A string \"%.80s ... %.80s\" exceeds the maximum Symbol "
357 "length of %d and has been truncated", name, (name + len - 80), Symbol::max_length());
358 len = Symbol::max_length();
359 }
360 return len;
361 }
362
363 Symbol* SymbolTable::new_symbol(const char* name, int len) {
364 len = check_length(name, len);
365 unsigned int hash = hash_symbol(name, len, _alt_hash);
366 Symbol* sym = lookup_common(name, len, hash);
367 if (sym == nullptr) {
368 sym = do_add_if_needed(name, len, hash, /* is_permanent */ false);
369 }
370 assert(sym->refcount() != 0, "lookup should have incremented the count");
371 assert(sym->equals(name, len), "symbol must be properly initialized");
372 return sym;
373 }
374
375 Symbol* SymbolTable::new_symbol(const Symbol* sym, int begin, int end) {
376 assert(begin <= end && end <= sym->utf8_length(), "just checking");
377 assert(sym->refcount() != 0, "require a valid symbol");
378 const char* name = (const char*)sym->base() + begin;
379 int len = end - begin;
380 assert(len <= Symbol::max_length(), "sanity");
381 unsigned int hash = hash_symbol(name, len, _alt_hash);
382 Symbol* found = lookup_common(name, len, hash);
383 if (found == nullptr) {
384 found = do_add_if_needed(name, len, hash, /* is_permanent */ false);
385 }
386 return found;
387 }
388
389 class SymbolTableLookup : StackObj {
390 private:
391 uintx _hash;
392 int _len;
393 const char* _str;
394 public:
395 SymbolTableLookup(const char* key, int len, uintx hash)
396 : _hash(hash), _len(len), _str(key) {}
397 uintx get_hash() const {
398 return _hash;
399 }
400 // Note: When equals() returns "true", the symbol's refcount is incremented. This is
401 // needed to ensure that the symbol is kept alive before equals() returns to the caller,
402 // so that another thread cannot clean the symbol up concurrently. The caller is
403 // responsible for decrementing the refcount, when the symbol is no longer needed.
404 bool equals(Symbol* value) {
405 assert(value != nullptr, "expected valid value");
406 Symbol *sym = value;
407 if (sym->equals(_str, _len)) {
408 if (sym->try_increment_refcount()) {
409 // something is referencing this symbol now.
410 return true;
411 } else {
412 assert(sym->refcount() == 0, "expected dead symbol");
413 return false;
414 }
415 } else {
416 return false;
417 }
418 }
419 bool is_dead(Symbol* value) {
420 return value->refcount() == 0;
421 }
422 };
423
424 class SymbolTableGet : public StackObj {
425 Symbol* _return;
426 public:
427 SymbolTableGet() : _return(nullptr) {}
428 void operator()(Symbol* value) {
429 assert(value != nullptr, "expected valid value");
430 _return = value;
431 }
432 Symbol* get_res_sym() const {
433 return _return;
434 }
435 };
436
437 void SymbolTable::update_needs_rehash(bool rehash) {
438 if (rehash) {
439 _needs_rehashing = true;
440 trigger_cleanup();
441 }
442 }
443
444 Symbol* SymbolTable::do_lookup(const char* name, int len, uintx hash) {
445 Thread* thread = Thread::current();
446 SymbolTableLookup lookup(name, len, hash);
447 SymbolTableGet stg;
448 bool rehash_warning = false;
449 _local_table->get(thread, lookup, stg, &rehash_warning);
450 update_needs_rehash(rehash_warning);
451 Symbol* sym = stg.get_res_sym();
452 assert((sym == nullptr) || sym->refcount() != 0, "found dead symbol");
453 return sym;
454 }
455
456 Symbol* SymbolTable::lookup_only(const char* name, int len, unsigned int& hash) {
457 hash = hash_symbol(name, len, _alt_hash);
458 return lookup_common(name, len, hash);
459 }
460
461 // Suggestion: Push unicode-based lookup all the way into the hashing
462 // and probing logic, so there is no need for convert_to_utf8 until
463 // an actual new Symbol* is created.
464 Symbol* SymbolTable::new_symbol(const jchar* name, int utf16_length) {
465 size_t utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
466 char stack_buf[ON_STACK_BUFFER_LENGTH];
467 if (utf8_length < sizeof(stack_buf)) {
468 char* chars = stack_buf;
469 UNICODE::convert_to_utf8(name, utf16_length, chars);
470 return new_symbol(chars, checked_cast<int>(utf8_length));
471 } else {
472 ResourceMark rm;
473 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
474 UNICODE::convert_to_utf8(name, utf16_length, chars);
475 return new_symbol(chars, checked_cast<int>(utf8_length));
476 }
477 }
478
479 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
480 unsigned int& hash) {
481 size_t utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
482 char stack_buf[ON_STACK_BUFFER_LENGTH];
483 if (utf8_length < sizeof(stack_buf)) {
484 char* chars = stack_buf;
485 UNICODE::convert_to_utf8(name, utf16_length, chars);
486 return lookup_only(chars, checked_cast<int>(utf8_length), hash);
487 } else {
488 ResourceMark rm;
489 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
490 UNICODE::convert_to_utf8(name, utf16_length, chars);
491 return lookup_only(chars, checked_cast<int>(utf8_length), hash);
492 }
493 }
494
495 void SymbolTable::new_symbols(ClassLoaderData* loader_data, const constantPoolHandle& cp,
496 int names_count, const char** names, int* lengths,
497 int* cp_indices, unsigned int* hashValues) {
498 // Note that is_permanent will be false for non-strong hidden classes.
499 // even if their loader is the boot loader because they will have a different cld.
500 bool is_permanent = loader_data->is_the_null_class_loader_data();
501 for (int i = 0; i < names_count; i++) {
502 const char *name = names[i];
503 int len = lengths[i];
504 assert(len <= Symbol::max_length(), "must be - these come from the constant pool");
505 unsigned int hash = hashValues[i];
506 assert(lookup_shared(name, len, hash) == nullptr, "must have checked already");
507 Symbol* sym = do_add_if_needed(name, len, hash, is_permanent);
508 assert(sym->refcount() != 0, "lookup should have incremented the count");
509 cp->symbol_at_put(cp_indices[i], sym);
510 }
511 }
512
513 Symbol* SymbolTable::do_add_if_needed(const char* name, int len, uintx hash, bool is_permanent) {
514 assert(len <= Symbol::max_length(), "caller should have ensured this");
515 SymbolTableLookup lookup(name, len, hash);
516 SymbolTableGet stg;
517 bool clean_hint = false;
518 bool rehash_warning = false;
519 Thread* current = Thread::current();
520 Symbol* sym;
521
522 ResourceMark rm(current);
523 const int alloc_size = Symbol::byte_size(len);
524 u1* u1_buf = NEW_RESOURCE_ARRAY_IN_THREAD(current, u1, alloc_size);
525 Symbol* tmp = ::new ((void*)u1_buf) Symbol((const u1*)name, len,
526 (is_permanent || CDSConfig::is_dumping_static_archive()) ? PERM_REFCOUNT : 1);
527
528 do {
529 if (_local_table->insert(current, lookup, *tmp, &rehash_warning, &clean_hint)) {
530 if (_local_table->get(current, lookup, stg, &rehash_warning)) {
531 sym = stg.get_res_sym();
532 // The get adds one to ref count, but we inserted with our ref already included.
533 // Therefore decrement with one.
534 if (sym->refcount() != PERM_REFCOUNT) {
535 sym->decrement_refcount();
536 }
537 break;
538 }
539 }
540
541 // In case another thread did a concurrent add, return value already in the table.
542 // This could fail if the symbol got deleted concurrently, so loop back until success.
543 if (_local_table->get(current, lookup, stg, &rehash_warning)) {
544 // The lookup added a refcount, which is ours.
545 sym = stg.get_res_sym();
546 break;
547 }
548 } while(true);
549
550 update_needs_rehash(rehash_warning);
551
552 if (clean_hint) {
553 mark_has_items_to_clean();
554 check_concurrent_work();
555 }
556
557 assert((sym == nullptr) || sym->refcount() != 0, "found dead symbol");
558 return sym;
559 }
560
561 Symbol* SymbolTable::new_permanent_symbol(const char* name) {
562 unsigned int hash = 0;
563 int len = check_length(name, (int)strlen(name));
564 Symbol* sym = SymbolTable::lookup_only(name, len, hash);
565 if (sym == nullptr) {
566 sym = do_add_if_needed(name, len, hash, /* is_permanent */ true);
567 }
568 if (!sym->is_permanent()) {
569 sym->make_permanent();
570 log_trace_symboltable_helper(sym, "Asked for a permanent symbol, but got a regular one");
571 }
572 return sym;
573 }
574
575 struct SizeFunc : StackObj {
576 size_t operator()(Symbol* value) {
577 assert(value != nullptr, "expected valid value");
578 return (value)->size() * HeapWordSize;
579 };
580 };
581
582 TableStatistics SymbolTable::get_table_statistics() {
583 static TableStatistics ts;
584 SizeFunc sz;
585 ts = _local_table->statistics_get(Thread::current(), sz, ts);
586 return ts;
587 }
588
589 void SymbolTable::print_table_statistics(outputStream* st) {
590 SizeFunc sz;
591 _local_table->statistics_to(Thread::current(), sz, st, "SymbolTable");
592
593 if (!_shared_table.empty()) {
594 _shared_table.print_table_statistics(st, "Shared Symbol Table");
595 }
596
597 if (!_dynamic_shared_table.empty()) {
598 _dynamic_shared_table.print_table_statistics(st, "Dynamic Shared Symbol Table");
599 }
600 }
601
602 // Verification
603 class VerifySymbols : StackObj {
604 public:
605 bool operator()(Symbol* value) {
606 guarantee(value != nullptr, "expected valid value");
607 Symbol* sym = value;
608 guarantee(sym->equals((const char*)sym->bytes(), sym->utf8_length()),
609 "symbol must be internally consistent");
610 return true;
611 };
612 };
613
614 void SymbolTable::verify() {
615 Thread* thr = Thread::current();
616 VerifySymbols vs;
617 if (!_local_table->try_scan(thr, vs)) {
618 log_info(symboltable)("verify unavailable at this moment");
619 }
620 }
621
622 static void print_symbol(outputStream* st, Symbol* sym) {
623 const char* utf8_string = (const char*)sym->bytes();
624 int utf8_length = sym->utf8_length();
625 st->print("%d %d: ", utf8_length, sym->refcount());
626 HashtableTextDump::put_utf8(st, utf8_string, utf8_length);
627 st->cr();
628 }
629
630 // Dumping
631 class DumpSymbol : StackObj {
632 Thread* _thr;
633 outputStream* _st;
634 public:
635 DumpSymbol(Thread* thr, outputStream* st) : _thr(thr), _st(st) {}
636 bool operator()(Symbol* value) {
637 assert(value != nullptr, "expected valid value");
638 print_symbol(_st, value);
639 return true;
640 };
641 };
642
643 class DumpSharedSymbol : StackObj {
644 outputStream* _st;
645 public:
646 DumpSharedSymbol(outputStream* st) : _st(st) {}
647 void do_value(Symbol* value) {
648 assert(value != nullptr, "value should point to a symbol");
649 print_symbol(_st, value);
650 };
651 };
652
653 void SymbolTable::dump(outputStream* st, bool verbose) {
654 if (!verbose) {
655 print_table_statistics(st);
656 } else {
657 Thread* thr = Thread::current();
658 ResourceMark rm(thr);
659 st->print_cr("VERSION: 1.1");
660 DumpSymbol ds(thr, st);
661 if (!_local_table->try_scan(thr, ds)) {
662 log_info(symboltable)("dump unavailable at this moment");
663 }
664 if (!_shared_table.empty()) {
665 st->print_cr("#----------------");
666 st->print_cr("# Shared symbols:");
667 st->print_cr("#----------------");
668 DumpSharedSymbol dss(st);
669 _shared_table.iterate(&dss);
670 }
671 if (!_dynamic_shared_table.empty()) {
672 st->print_cr("#------------------------");
673 st->print_cr("# Dynamic shared symbols:");
674 st->print_cr("#------------------------");
675 DumpSharedSymbol dss(st);
676 _dynamic_shared_table.iterate(&dss);
677 }
678 }
679 }
680
681 #if INCLUDE_CDS
682 void SymbolTable::copy_shared_symbol_table(GrowableArray<Symbol*>* symbols,
683 CompactHashtableWriter* writer) {
684 ArchiveBuilder* builder = ArchiveBuilder::current();
685 int len = symbols->length();
686 for (int i = 0; i < len; i++) {
687 Symbol* sym = ArchiveBuilder::get_buffered_symbol(symbols->at(i));
688 unsigned int fixed_hash = hash_shared_symbol((const char*)sym->bytes(), sym->utf8_length());
689 assert(fixed_hash == hash_symbol((const char*)sym->bytes(), sym->utf8_length(), false),
690 "must not rehash during dumping");
691 sym->set_permanent();
692 writer->add(fixed_hash, builder->buffer_to_offset_u4((address)sym));
693 }
694 }
695
696 size_t SymbolTable::estimate_size_for_archive() {
697 if (_items_count > (size_t)max_jint) {
698 fatal("Too many symbols to be archived: %zu", _items_count);
699 }
700 return CompactHashtableWriter::estimate_size(int(_items_count));
701 }
702
703 void SymbolTable::write_to_archive(GrowableArray<Symbol*>* symbols) {
704 CompactHashtableWriter writer(int(_items_count), ArchiveBuilder::symbol_stats());
705 copy_shared_symbol_table(symbols, &writer);
706 if (CDSConfig::is_dumping_static_archive()) {
707 _shared_table.reset();
708 writer.dump(&_shared_table, "symbol");
709 } else {
710 assert(CDSConfig::is_dumping_dynamic_archive(), "must be");
711 _dynamic_shared_table.reset();
712 writer.dump(&_dynamic_shared_table, "symbol");
713 }
714 }
715
716 void SymbolTable::serialize_shared_table_header(SerializeClosure* soc,
717 bool is_static_archive) {
718 OffsetCompactHashtable<const char*, Symbol*, symbol_equals_compact_hashtable_entry> * table;
719 if (is_static_archive) {
720 table = &_shared_table;
721 } else {
722 table = &_dynamic_shared_table;
723 }
724 table->serialize_header(soc);
725 if (soc->writing()) {
726 // Sanity. Make sure we don't use the shared table at dump time
727 table->reset();
728 }
729 }
730 #endif //INCLUDE_CDS
731
732 // Concurrent work
733 void SymbolTable::grow(JavaThread* jt) {
734 SymbolTableHash::GrowTask gt(_local_table);
735 if (!gt.prepare(jt)) {
736 return;
737 }
738 log_trace(symboltable)("Started to grow");
739 {
740 TraceTime timer("Grow", TRACETIME_LOG(Debug, symboltable, perf));
741 while (gt.do_task(jt)) {
742 gt.pause(jt);
743 {
744 ThreadBlockInVM tbivm(jt);
745 }
746 gt.cont(jt);
747 }
748 }
749 gt.done(jt);
750 _current_size = table_size();
751 log_debug(symboltable)("Grown to size:%zu", _current_size);
752 }
753
754 struct SymbolTableDoDelete : StackObj {
755 size_t _deleted;
756 SymbolTableDoDelete() : _deleted(0) {}
757 void operator()(Symbol* value) {
758 assert(value != nullptr, "expected valid value");
759 Symbol *sym = value;
760 assert(sym->refcount() == 0, "refcount");
761 _deleted++;
762 }
763 };
764
765 struct SymbolTableDeleteCheck : StackObj {
766 size_t _processed;
767 SymbolTableDeleteCheck() : _processed(0) {}
768 bool operator()(Symbol* value) {
769 assert(value != nullptr, "expected valid value");
770 _processed++;
771 Symbol *sym = value;
772 return (sym->refcount() == 0);
773 }
774 };
775
776 void SymbolTable::clean_dead_entries(JavaThread* jt) {
777 SymbolTableHash::BulkDeleteTask bdt(_local_table);
778 if (!bdt.prepare(jt)) {
779 return;
780 }
781
782 SymbolTableDeleteCheck stdc;
783 SymbolTableDoDelete stdd;
784 NativeHeapTrimmer::SuspendMark sm("symboltable");
785 {
786 TraceTime timer("Clean", TRACETIME_LOG(Debug, symboltable, perf));
787 while (bdt.do_task(jt, stdc, stdd)) {
788 bdt.pause(jt);
789 {
790 ThreadBlockInVM tbivm(jt);
791 }
792 bdt.cont(jt);
793 }
794 reset_has_items_to_clean();
795 bdt.done(jt);
796 }
797
798 Atomic::add(&_symbols_counted, stdc._processed);
799
800 log_debug(symboltable)("Cleaned %zu of %zu",
801 stdd._deleted, stdc._processed);
802 }
803
804 void SymbolTable::check_concurrent_work() {
805 if (has_work()) {
806 return;
807 }
808 // We should clean/resize if we have
809 // more items than preferred load factor or
810 // more dead items than water mark.
811 if (has_items_to_clean() || (get_load_factor() > PREF_AVG_LIST_LEN)) {
812 log_debug(symboltable)("Concurrent work triggered, load factor: %f, items to clean: %s",
813 get_load_factor(), has_items_to_clean() ? "true" : "false");
814 trigger_cleanup();
815 }
816 }
817
818 bool SymbolTable::should_grow() {
819 return get_load_factor() > PREF_AVG_LIST_LEN && !_local_table->is_max_size_reached();
820 }
821
822 void SymbolTable::do_concurrent_work(JavaThread* jt) {
823 // Rehash if needed. Rehashing goes to a safepoint but the rest of this
824 // work is concurrent.
825 if (needs_rehashing() && maybe_rehash_table()) {
826 Atomic::release_store(&_has_work, false);
827 return; // done, else grow
828 }
829 log_debug(symboltable, perf)("Concurrent work, live factor: %g", get_load_factor());
830 // We prefer growing, since that also removes dead items
831 if (should_grow()) {
832 grow(jt);
833 } else {
834 clean_dead_entries(jt);
835 }
836 Atomic::release_store(&_has_work, false);
837 }
838
839 // Called at VM_Operation safepoint
840 void SymbolTable::rehash_table() {
841 assert(SafepointSynchronize::is_at_safepoint(), "must be called at safepoint");
842 // The ServiceThread initiates the rehashing so it is not resizing.
843 assert (_local_table->is_safepoint_safe(), "Should not be resizing now");
844
845 _alt_hash_seed = AltHashing::compute_seed();
846
847 // We use current size
848 size_t new_size = _local_table->get_size_log2(Thread::current());
849 SymbolTableHash* new_table = new SymbolTableHash(new_size, END_SIZE, REHASH_LEN, true);
850 // Use alt hash from now on
851 _alt_hash = true;
852 _local_table->rehash_nodes_to(Thread::current(), new_table);
853
854 // free old table
855 delete _local_table;
856 _local_table = new_table;
857
858 _rehashed = true;
859 _needs_rehashing = false;
860 }
861
862 bool SymbolTable::maybe_rehash_table() {
863 log_debug(symboltable)("Table imbalanced, rehashing called.");
864
865 // Grow instead of rehash.
866 if (should_grow()) {
867 log_debug(symboltable)("Choosing growing over rehashing.");
868 _needs_rehashing = false;
869 return false;
870 }
871
872 // Already rehashed.
873 if (_rehashed) {
874 log_warning(symboltable)("Rehashing already done, still long lists.");
875 _needs_rehashing = false;
876 return false;
877 }
878
879 VM_RehashSymbolTable op;
880 VMThread::execute(&op);
881 return true;
882 }
883
884 //---------------------------------------------------------------------------
885 // Non-product code
886
887 #ifndef PRODUCT
888
889 class HistogramIterator : StackObj {
890 public:
891 static const size_t results_length = 100;
892 size_t counts[results_length];
893 size_t sizes[results_length];
894 size_t total_size;
895 size_t total_count;
896 size_t total_length;
897 size_t max_length;
898 size_t out_of_range_count;
899 size_t out_of_range_size;
900 HistogramIterator() : total_size(0), total_count(0), total_length(0),
901 max_length(0), out_of_range_count(0), out_of_range_size(0) {
902 // initialize results to zero
903 for (size_t i = 0; i < results_length; i++) {
904 counts[i] = 0;
905 sizes[i] = 0;
906 }
907 }
908 bool operator()(Symbol* value) {
909 assert(value != nullptr, "expected valid value");
910 Symbol* sym = value;
911 size_t size = sym->size();
912 size_t len = sym->utf8_length();
913 if (len < results_length) {
914 counts[len]++;
915 sizes[len] += size;
916 } else {
917 out_of_range_count++;
918 out_of_range_size += size;
919 }
920 total_count++;
921 total_size += size;
922 total_length += len;
923 max_length = MAX2(max_length, len);
924
925 return true;
926 };
927 };
928
929 void SymbolTable::print_histogram() {
930 HistogramIterator hi;
931 _local_table->do_scan(Thread::current(), hi);
932 tty->print_cr("Symbol Table Histogram:");
933 tty->print_cr(" Total number of symbols %7zu", hi.total_count);
934 tty->print_cr(" Total size in memory %7zuK", (hi.total_size * wordSize) / K);
935 tty->print_cr(" Total counted %7zu", _symbols_counted);
936 tty->print_cr(" Total removed %7zu", _symbols_removed);
937 if (_symbols_counted > 0) {
938 tty->print_cr(" Percent removed %3.2f",
939 ((double)_symbols_removed / (double)_symbols_counted) * 100);
940 }
941 tty->print_cr(" Reference counts %7zu", Symbol::_total_count);
942 tty->print_cr(" Symbol arena used %7zuK", arena()->used() / K);
943 tty->print_cr(" Symbol arena size %7zuK", arena()->size_in_bytes() / K);
944 tty->print_cr(" Total symbol length %7zu", hi.total_length);
945 tty->print_cr(" Maximum symbol length %7zu", hi.max_length);
946 tty->print_cr(" Average symbol length %7.2f", ((double)hi.total_length / (double)hi.total_count));
947 tty->print_cr(" Symbol length histogram:");
948 tty->print_cr(" %6s %10s %10s", "Length", "#Symbols", "Size");
949 for (size_t i = 0; i < hi.results_length; i++) {
950 if (hi.counts[i] > 0) {
951 tty->print_cr(" %6zu %10zu %10zuK",
952 i, hi.counts[i], (hi.sizes[i] * wordSize) / K);
953 }
954 }
955 tty->print_cr(" >= %6zu %10zu %10zuK\n",
956 hi.results_length, hi.out_of_range_count, (hi.out_of_range_size*wordSize) / K);
957 }
958 #endif // PRODUCT
959
960 // Utility for dumping symbols
961 SymboltableDCmd::SymboltableDCmd(outputStream* output, bool heap) :
962 DCmdWithParser(output, heap),
963 _verbose("-verbose", "Dump the content of each symbol in the table",
964 "BOOLEAN", false, "false") {
965 _dcmdparser.add_dcmd_option(&_verbose);
966 }
967
968 void SymboltableDCmd::execute(DCmdSource source, TRAPS) {
969 VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSymbols,
970 _verbose.value());
971 VMThread::execute(&dumper);
972 }