1 /*
2 * Copyright (c) 1997, 2018, 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.inline.hpp"
28 #include "classfile/javaClasses.hpp"
29 #include "classfile/symbolTable.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/metaspaceClosure.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/atomic.hpp"
35 #include "runtime/interfaceSupport.inline.hpp"
36 #include "runtime/timerTrace.hpp"
37 #include "services/diagnosticCommand.hpp"
38 #include "utilities/concurrentHashTable.inline.hpp"
39 #include "utilities/concurrentHashTableTasks.inline.hpp"
40
41 // We used to not resize at all, so let's be conservative
42 // and not set it too short before we decide to resize,
43 // to match previous startup behavior
44 #define PREF_AVG_LIST_LEN 8
45 // 2^17 (131,072) is max size, which is about 6.5 times as large
46 // as the previous table size (used to be 20,011),
47 // which never resized
48 #define END_SIZE 17
49 // If a chain gets to 100 something might be wrong
50 #define REHASH_LEN 100
51 // We only get a chance to check whether we need
52 // to clean infrequently (on class unloading),
53 // so if we have even one dead entry then mark table for cleaning
54 #define CLEAN_DEAD_HIGH_WATER_MARK 0.0
55
56 #define ON_STACK_BUFFER_LENGTH 128
57
58 // --------------------------------------------------------------------------
59 SymbolTable* SymbolTable::_the_table = NULL;
60 CompactHashtable<Symbol*, char> SymbolTable::_shared_table;
61 bool SymbolTable::_alt_hash = false;
62 // Static arena for symbols that are not deallocated
63 Arena* SymbolTable::_arena = NULL;
64 bool SymbolTable::_lookup_shared_first = false;
65 int SymbolTable::_symbols_removed = 0;
66 int SymbolTable::_symbols_counted = 0;
67
68 static juint murmur_seed = 0;
69
70 static inline void _log_trace_symboltable_helper(Symbol* sym, const char* msg) {
71 #ifndef PRODUCT
72 if (log_is_enabled(Trace, symboltable)) {
73 char *s;
74 {
75 ResourceMark rm;
76 s = sym->as_quoted_ascii();
77 s = os::strdup(s);
78 }
79 if (s == NULL) {
80 log_trace(symboltable)("%s [%s]", msg, "NULL");
81 } else {
82 log_trace(symboltable)("%s [%s]", msg, s);
83 os::free(s);
84 }
85 }
86 #endif // PRODUCT
87 }
88
89 // Pick hashing algorithm.
90 static uintx hash_symbol(const char* s, int len, bool useAlt) {
91 return useAlt ?
92 AltHashing::murmur3_32(murmur_seed, (const jbyte*)s, len) :
93 java_lang_String::hash_code((const jbyte*)s, len);
94 }
95
96 static uintx hash_shared_symbol(const char* s, int len) {
97 return java_lang_String::hash_code((const jbyte*)s, len);
98 }
99
100 class SymbolTableConfig : public SymbolTableHash::BaseConfig {
101 private:
102 public:
103 static uintx get_hash(Symbol* const& value, bool* is_dead) {
104 *is_dead = (value->refcount() == 0);
105 if (*is_dead) {
106 return 0;
107 } else {
108 return hash_symbol((char*)value->bytes(), value->utf8_length(), SymbolTable::_alt_hash);
109 }
110 }
111 // We use default allocation/deallocation but counted
112 static void* allocate_node(size_t size, Symbol* const& value) {
113 SymbolTable::item_added();
114 return SymbolTableHash::BaseConfig::allocate_node(size, value);
115 }
116 static void free_node(void* memory, Symbol* const& value) {
117 // We get here either because #1 some threads lost a race
118 // to insert a newly created Symbol, or #2 we are freeing
119 // a symbol during normal cleanup deletion.
120 // If #1, then the symbol can be a permanent (refcount==PERM_REFCOUNT),
121 // or regular newly created one but with refcount==0 (see SymbolTableCreateEntry)
122 // If #2, then the symbol must have refcount==0
123 assert((value->refcount() == PERM_REFCOUNT) || (value->refcount() == 0),
124 "refcount %d", value->refcount());
125 SymbolTable::delete_symbol(value);
126 SymbolTableHash::BaseConfig::free_node(memory, value);
127 SymbolTable::item_removed();
128 }
129 };
130
131 static size_t ceil_pow_2(uintx value) {
132 size_t ret;
133 for (ret = 1; ((size_t)1 << ret) < value; ++ret);
134 return ret;
135 }
136
137 SymbolTable::SymbolTable() : _local_table(NULL), _current_size(0), _has_work(0),
138 _needs_rehashing(false), _items(0), _uncleaned_items(0) {
139
140 size_t start_size_log_2 = ceil_pow_2(SymbolTableSize);
141 _current_size = ((size_t)1) << start_size_log_2;
142 log_trace(symboltable)("Start size: " SIZE_FORMAT " (" SIZE_FORMAT ")",
143 _current_size, start_size_log_2);
144 _local_table = new SymbolTableHash(start_size_log_2, END_SIZE, REHASH_LEN);
145 }
146
147 void SymbolTable::delete_symbol(Symbol* sym) {
148 if (sym->refcount() == PERM_REFCOUNT) {
149 MutexLocker ml(SymbolTable_lock); // Protect arena
150 // Deleting permanent symbol should not occur very often (insert race condition),
151 // so log it.
152 _log_trace_symboltable_helper(sym, "Freeing permanent symbol");
153 if (!arena()->Afree(sym, sym->size())) {
154 _log_trace_symboltable_helper(sym, "Leaked permanent symbol");
155 }
156 } else {
157 delete sym;
158 }
159 }
160
161 size_t SymbolTable::item_added() {
162 return Atomic::add(1, &(SymbolTable::the_table()->_items));
163 }
164
165 void SymbolTable::set_item_clean_count(size_t ncl) {
166 Atomic::store((int)ncl, &(SymbolTable::the_table()->_uncleaned_items));
167 log_trace(symboltable)("Set uncleaned items:" INT32_FORMAT, SymbolTable::the_table()->_uncleaned_items);
168 }
169
170 void SymbolTable::mark_item_clean_count() {
171 if (Atomic::cmpxchg(1, &(SymbolTable::the_table()->_uncleaned_items), 0) == 0) { // only mark if unset
172 log_trace(symboltable)("Marked uncleaned items:" INT32_FORMAT, SymbolTable::the_table()->_uncleaned_items);
173 }
174 }
175
176 void SymbolTable::item_removed() {
177 Atomic::add(1, &(SymbolTable::the_table()->_symbols_removed));
178 Atomic::sub(1, &(SymbolTable::the_table()->_items));
179 }
180
181 double SymbolTable::get_load_factor() {
182 return (_items*1.0)/_current_size;
183 }
184
185 double SymbolTable::get_dead_factor() {
186 return (_uncleaned_items*1.0)/_current_size;
187 }
188
189 size_t SymbolTable::table_size(Thread* thread) {
190 return ((size_t)(1)) << _local_table->get_size_log2(thread != NULL ? thread
191 : Thread::current());
192 }
193
194 void SymbolTable::trigger_concurrent_work() {
195 MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
196 SymbolTable::the_table()->_has_work = true;
197 Service_lock->notify_all();
198 }
199
200 Symbol* SymbolTable::allocate_symbol(const u1* name, int len, bool c_heap, TRAPS) {
201 assert (len <= Symbol::max_length(), "should be checked by caller");
202
203 Symbol* sym;
204 if (DumpSharedSpaces) {
205 c_heap = false;
206 }
207 if (c_heap) {
208 // refcount starts as 1
209 sym = new (len, THREAD) Symbol(name, len, 1);
210 assert(sym != NULL, "new should call vm_exit_out_of_memory if C_HEAP is exhausted");
211 } else {
212 // Allocate to global arena
213 MutexLocker ml(SymbolTable_lock); // Protect arena
214 sym = new (len, arena(), THREAD) Symbol(name, len, PERM_REFCOUNT);
215 }
216 return sym;
217 }
218
219 void SymbolTable::initialize_symbols(int arena_alloc_size) {
220 // Initialize the arena for global symbols, size passed in depends on CDS.
221 if (arena_alloc_size == 0) {
222 _arena = new (mtSymbol) Arena(mtSymbol);
223 } else {
224 _arena = new (mtSymbol) Arena(mtSymbol, arena_alloc_size);
225 }
226 }
227
228 class SymbolsDo : StackObj {
229 SymbolClosure *_cl;
230 public:
231 SymbolsDo(SymbolClosure *cl) : _cl(cl) {}
232 bool operator()(Symbol** value) {
233 assert(value != NULL, "expected valid value");
234 assert(*value != NULL, "value should point to a symbol");
235 _cl->do_symbol(value);
236 return true;
237 };
238 };
239
240 // Call function for all symbols in the symbol table.
241 void SymbolTable::symbols_do(SymbolClosure *cl) {
242 // all symbols from shared table
243 _shared_table.symbols_do(cl);
244
245 // all symbols from the dynamic table
246 SymbolsDo sd(cl);
247 if (!SymbolTable::the_table()->_local_table->try_scan(Thread::current(), sd)) {
248 log_info(stringtable)("symbols_do unavailable at this moment");
249 }
250 }
251
252 class MetaspacePointersDo : StackObj {
253 MetaspaceClosure *_it;
254 public:
255 MetaspacePointersDo(MetaspaceClosure *it) : _it(it) {}
256 bool operator()(Symbol** value) {
257 assert(value != NULL, "expected valid value");
258 assert(*value != NULL, "value should point to a symbol");
259 _it->push(value);
260 return true;
261 };
262 };
263
264 void SymbolTable::metaspace_pointers_do(MetaspaceClosure* it) {
265 assert(DumpSharedSpaces, "called only during dump time");
266 MetaspacePointersDo mpd(it);
267 SymbolTable::the_table()->_local_table->do_scan(Thread::current(), mpd);
268 }
269
270 Symbol* SymbolTable::lookup_dynamic(const char* name,
271 int len, unsigned int hash) {
272 Symbol* sym = SymbolTable::the_table()->do_lookup((char*)name, len, hash);
273 assert((sym == NULL) || sym->refcount() != 0, "refcount must not be zero");
274 return sym;
275 }
276
277 Symbol* SymbolTable::lookup_shared(const char* name,
278 int len, unsigned int hash) {
279 if (!_shared_table.empty()) {
280 if (SymbolTable::_alt_hash) {
281 // hash_code parameter may use alternate hashing algorithm but the shared table
282 // always uses the same original hash code.
283 hash = hash_shared_symbol(name, len);
284 }
285 return _shared_table.lookup(name, hash, len);
286 } else {
287 return NULL;
288 }
289 }
290
291 Symbol* SymbolTable::lookup_common(const char* name,
292 int len, unsigned int hash) {
293 Symbol* sym;
294 if (_lookup_shared_first) {
295 sym = lookup_shared(name, len, hash);
296 if (sym == NULL) {
297 _lookup_shared_first = false;
298 sym = lookup_dynamic(name, len, hash);
299 }
300 } else {
301 sym = lookup_dynamic(name, len, hash);
302 if (sym == NULL) {
303 sym = lookup_shared(name, len, hash);
304 if (sym != NULL) {
305 _lookup_shared_first = true;
306 }
307 }
308 }
309 return sym;
310 }
311
312 Symbol* SymbolTable::lookup(const char* name, int len, TRAPS) {
313 unsigned int hash = hash_symbol(name, len, SymbolTable::_alt_hash);
314 Symbol* sym = SymbolTable::the_table()->lookup_common(name, len, hash);
315 if (sym == NULL) {
316 sym = SymbolTable::the_table()->do_add_if_needed((char*)name, len, hash, true, CHECK_NULL);
317 }
318 assert(sym->refcount() != 0, "lookup should have incremented the count");
319 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
320 return sym;
321 }
322
323 Symbol* SymbolTable::lookup(const Symbol* sym, int begin, int end, TRAPS) {
324 Symbol* found = NULL;
325 {
326 debug_only(NoSafepointVerifier nsv;)
327
328 char* name = (char*)sym->base() + begin;
329 int len = end - begin;
330 unsigned int hash = hash_symbol(name, len, SymbolTable::_alt_hash);
331 found = SymbolTable::the_table()->do_add_if_needed(name, len, hash, true, THREAD);
332 }
333 return found;
334 }
335
336 class SymbolTableLookupChar : StackObj {
337 private:
338 Thread* _thread;
339 uintx _hash;
340 int _len;
341 const char* _str;
342 Symbol* _found;
343 public:
344 SymbolTableLookupChar(Thread* thread, const char* key, int len, uintx hash)
345 : _thread(thread), _hash(hash), _str(key), _len(len) , _found(NULL) {
346 }
347 uintx get_hash() const {
348 return _hash;
349 }
350 bool equals(Symbol** value, bool* is_dead) {
351 assert(value != NULL, "expected valid value");
352 assert(*value != NULL, "value should point to a symbol");
353 Symbol *sym = *value;
354 if (sym->equals(_str, _len)) {
355 if (sym->try_increment_refcount()) {
356 // something is referencing this symbol now.
357 _found = sym;
358 return true;
359 } else {
360 *is_dead = (sym->refcount() == 0);
361 return false;
362 }
363 } else {
364 return false;
365 }
366 }
367 };
368
369 class SymbolTableGet : public StackObj {
370 Symbol* _return;
371 public:
372 SymbolTableGet() : _return(NULL) { }
373 void operator()(Symbol** value) {
374 assert(value != NULL, "expected valid value");
375 assert(*value != NULL, "value should point to a symbol");
376 _return = *value;
377 }
378 Symbol* get_res_sym() {
379 return _return;
380 }
381 };
382
383 Symbol* SymbolTable::do_lookup(char* name, int len, uintx hash) {
384 Thread* thread = Thread::current();
385 SymbolTableLookupChar lookup(thread, name, len, hash);
386 SymbolTableGet stg;
387 bool rehash_warning;
388 _local_table->get(thread, lookup, stg, &rehash_warning);
389 if (rehash_warning) {
390 _needs_rehashing = true;
391 }
392 Symbol* sym = stg.get_res_sym();
393 assert((sym == NULL) || sym->refcount() != 0, "found dead symbol");
394 return sym;
395 }
396
397 Symbol* SymbolTable::lookup_only(const char* name, int len, unsigned int& hash) {
398 hash = hash_symbol(name, len, SymbolTable::_alt_hash);
399 return SymbolTable::the_table()->lookup_common(name, len, hash);
400 }
401
402 // Suggestion: Push unicode-based lookup all the way into the hashing
403 // and probing logic, so there is no need for convert_to_utf8 until
404 // an actual new Symbol* is created.
405 Symbol* SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
406 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
407 char stack_buf[ON_STACK_BUFFER_LENGTH];
408 if (utf8_length < (int) sizeof(stack_buf)) {
409 char* chars = stack_buf;
410 UNICODE::convert_to_utf8(name, utf16_length, chars);
411 return lookup(chars, utf8_length, THREAD);
412 } else {
413 ResourceMark rm(THREAD);
414 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
415 UNICODE::convert_to_utf8(name, utf16_length, chars);
416 return lookup(chars, utf8_length, THREAD);
417 }
418 }
419
420 Symbol* SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
421 unsigned int& hash) {
422 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
423 char stack_buf[ON_STACK_BUFFER_LENGTH];
424 if (utf8_length < (int) sizeof(stack_buf)) {
425 char* chars = stack_buf;
426 UNICODE::convert_to_utf8(name, utf16_length, chars);
427 return lookup_only(chars, utf8_length, hash);
428 } else {
429 ResourceMark rm;
430 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);
431 UNICODE::convert_to_utf8(name, utf16_length, chars);
432 return lookup_only(chars, utf8_length, hash);
433 }
434 }
435
436 void SymbolTable::add(ClassLoaderData* loader_data, const constantPoolHandle& cp,
437 int names_count, const char** names, int* lengths,
438 int* cp_indices, unsigned int* hashValues, TRAPS) {
439 bool c_heap = !loader_data->is_the_null_class_loader_data();
440 for (int i=0; i<names_count; i++) {
441 char *name = (char*)names[i];
442 int len = lengths[i];
443 unsigned int hash = hashValues[i];
444 Symbol* sym = SymbolTable::the_table()->lookup_common(name, len, hash);
445 if (sym == NULL) {
446 sym = SymbolTable::the_table()->do_add_if_needed(name, len, hash, c_heap, CHECK);
447 }
448 assert(sym->refcount()!=0, "lookup should have incremented the count");
449 cp->symbol_at_put(cp_indices[i], sym);
450 }
451 }
452
453 class SymbolTableCreateEntry : public StackObj {
454 private:
455 Thread* _thread;
456 const char* _name;
457 int _len;
458 bool _heap;
459 Symbol* _return;
460 Symbol* _created;
461
462 #ifdef ASSERT
463 void _assert_for_name(Symbol* sym, const char* where) const {
464 assert(sym->utf8_length() == _len, "%s [%d,%d]", where, sym->utf8_length(), _len);
465 for (int i=0; i<_len; i++) {
466 assert(sym->byte_at(i) == _name[i],
467 "%s [%d,%d,%d]", where, i, sym->byte_at(i), _name[i]);
468 }
469 }
470 #endif
471
472 public:
473 SymbolTableCreateEntry(Thread* thread, const char* name, int len, bool heap)
474 : _thread(thread), _name(name) , _len(len), _heap(heap), _return(NULL) , _created(NULL) {
475 assert(_name != NULL, "expected valid name");
476 }
477 Symbol* operator()() {
478 _created = SymbolTable::the_table()->allocate_symbol((const u1*)_name, _len, _heap, _thread);
479 assert(_created != NULL, "expected created symbol");
480 #ifdef ASSERT
481 _assert_for_name(_created, "operator()()");
482 #endif
483 assert(_created->equals((char*)_name, _len),
484 "symbol must be properly initialized [%p,%d,%d]", _name, _len, (int)_heap);
485 return _created;
486 }
487 void operator()(bool inserted, Symbol** value) {
488 assert(value != NULL, "expected valid value");
489 assert(*value != NULL, "value should point to a symbol");
490 if (!inserted && (_created != NULL)) {
491 // We created our symbol, but someone else inserted
492 // theirs first, so ours will be destroyed.
493 // Since symbols are created with refcount of 1,
494 // we must decrement it here to 0 to delete,
495 // unless it's a permanent one.
496 if (_created->refcount() != PERM_REFCOUNT) {
497 assert(_created->refcount() == 1, "expected newly created symbol");
498 _created->decrement_refcount();
499 assert(_created->refcount() == 0, "expected dead symbol");
500 }
501 }
502 _return = *value;
503 #ifdef ASSERT
504 _assert_for_name(_return, "operator()");
505 #endif
506 }
507 Symbol* get_new_sym() const {
508 #ifdef ASSERT
509 _assert_for_name(_return, "get_new_sym");
510 #endif
511 return _return;
512 }
513 };
514
515 Symbol* SymbolTable::do_add_if_needed(char* name, int len, uintx hash, bool heap, TRAPS) {
516 SymbolTableLookupChar lookup(THREAD, name, len, hash);
517 SymbolTableCreateEntry stce(THREAD, name, len, heap);
518 bool rehash_warning;
519 bool clean_hint;
520 _local_table->get_insert_lazy(THREAD, lookup, stce, stce, &rehash_warning, &clean_hint);
521 if (rehash_warning) {
522 _needs_rehashing = true;
523 }
524 if (clean_hint) {
525 // we just found out that there is a dead item,
526 // which we were unable to clean right now,
527 // but we have no way of telling whether it's
528 // been previously counted or not, so mark
529 // it only if no other items were found yet
530 mark_item_clean_count();
531 check_concurrent_work();
532 }
533 Symbol* sym = stce.get_new_sym();
534 assert(sym->refcount() != 0, "zero is invalid");
535 return sym;
536 }
537
538 Symbol* SymbolTable::new_permanent_symbol(const char* name, TRAPS) {
539 unsigned int hash = 0;
540 int len = (int)strlen(name);
541 Symbol* sym = SymbolTable::lookup_only(name, len, hash);
542 if (sym == NULL) {
543 sym = SymbolTable::the_table()->do_add_if_needed((char*)name, len, hash, false, CHECK_NULL);
544 }
545 if (sym->refcount() != PERM_REFCOUNT) {
546 sym->increment_refcount();
547 _log_trace_symboltable_helper(sym, "Asked for a permanent symbol, but got a regular one");
548 }
549 return sym;
550 }
551
552 struct SizeFunc : StackObj {
553 size_t operator()(Symbol** value) {
554 assert(value != NULL, "expected valid value");
555 assert(*value != NULL, "value should point to a symbol");
556 return (*value)->size() * HeapWordSize;
557 };
558 };
559
560 void SymbolTable::print_table_statistics(outputStream* st,
561 const char* table_name) {
562 SizeFunc sz;
563 _local_table->statistics_to(Thread::current(), sz, st, table_name);
564 }
565
566 // Verification
567 class VerifySymbols : StackObj {
568 public:
569 bool operator()(Symbol** value) {
570 guarantee(value != NULL, "expected valid value");
571 guarantee(*value != NULL, "value should point to a symbol");
572 Symbol* sym = *value;
573 guarantee(sym->equals((char*)sym->bytes(), sym->utf8_length()),
574 "symbol must be internally consistent");
575 return true;
576 };
577 };
578
579 void SymbolTable::verify() {
580 Thread* thr = Thread::current();
581 VerifySymbols vs;
582 if (!SymbolTable::the_table()->_local_table->try_scan(thr, vs)) {
583 log_info(stringtable)("verify unavailable at this moment");
584 }
585 }
586
587 // Dumping
588 class DumpSymbol : StackObj {
589 Thread* _thr;
590 outputStream* _st;
591 public:
592 DumpSymbol(Thread* thr, outputStream* st) : _thr(thr), _st(st) {}
593 bool operator()(Symbol** value) {
594 assert(value != NULL, "expected valid value");
595 assert(*value != NULL, "value should point to a symbol");
596 Symbol* sym = *value;
597 const char* utf8_string = (const char*)sym->bytes();
598 int utf8_length = sym->utf8_length();
599 _st->print("%d %d: ", utf8_length, sym->refcount());
600 HashtableTextDump::put_utf8(_st, utf8_string, utf8_length);
601 _st->cr();
602 return true;
603 };
604 };
605
606 void SymbolTable::dump(outputStream* st, bool verbose) {
607 if (!verbose) {
608 SymbolTable::the_table()->print_table_statistics(st, "SymbolTable");
609 } else {
610 Thread* thr = Thread::current();
611 ResourceMark rm(thr);
612 st->print_cr("VERSION: 1.1");
613 DumpSymbol ds(thr, st);
614 if (!SymbolTable::the_table()->_local_table->try_scan(thr, ds)) {
615 log_info(symboltable)("dump unavailable at this moment");
616 }
617 }
618 }
619
620 #if INCLUDE_CDS
621 struct CopyToArchive : StackObj {
622 CompactSymbolTableWriter* _writer;
623 CopyToArchive(CompactSymbolTableWriter* writer) : _writer(writer) {}
624 bool operator()(Symbol** value) {
625 assert(value != NULL, "expected valid value");
626 assert(*value != NULL, "value should point to a symbol");
627 Symbol* sym = *value;
628 unsigned int fixed_hash = hash_shared_symbol((char*)sym->bytes(), sym->utf8_length());
629 if (fixed_hash == 0) {
630 return true;
631 }
632 assert(fixed_hash == hash_symbol((char*)sym->bytes(), sym->utf8_length(), false),
633 "must not rehash during dumping");
634
635 // add to the compact table
636 _writer->add(fixed_hash, sym);
637
638 return true;
639 }
640 };
641
642 void SymbolTable::copy_shared_symbol_table(CompactSymbolTableWriter* writer) {
643 CopyToArchive copy(writer);
644 SymbolTable::the_table()->_local_table->do_scan(Thread::current(), copy);
645 }
646
647 void SymbolTable::write_to_archive() {
648 _shared_table.reset();
649
650 int num_buckets = (SymbolTable::the_table()->_items / SharedSymbolTableBucketSize);
651 // calculation of num_buckets can result in zero buckets, we need at least one
652 CompactSymbolTableWriter writer(num_buckets > 1 ? num_buckets : 1,
653 &MetaspaceShared::stats()->symbol);
654 copy_shared_symbol_table(&writer);
655 writer.dump(&_shared_table);
656
657 // Verify table is correct
658 Symbol* sym = vmSymbols::java_lang_Object();
659 const char* name = (const char*)sym->bytes();
660 int len = sym->utf8_length();
661 unsigned int hash = hash_symbol(name, len, SymbolTable::_alt_hash);
662 assert(sym == _shared_table.lookup(name, hash, len), "sanity");
663 }
664
665 void SymbolTable::serialize(SerializeClosure* soc) {
666 _shared_table.set_type(CompactHashtable<Symbol*, char>::_symbol_table);
667 _shared_table.serialize(soc);
668
669 if (soc->writing()) {
670 // Sanity. Make sure we don't use the shared table at dump time
671 _shared_table.reset();
672 }
673 }
674 #endif //INCLUDE_CDS
675
676 // Concurrent work
677 void SymbolTable::grow(JavaThread* jt) {
678 SymbolTableHash::GrowTask gt(_local_table);
679 if (!gt.prepare(jt)) {
680 return;
681 }
682 log_trace(symboltable)("Started to grow");
683 {
684 TraceTime timer("Grow", TRACETIME_LOG(Debug, symboltable, perf));
685 while (gt.do_task(jt)) {
686 gt.pause(jt);
687 {
688 ThreadBlockInVM tbivm(jt);
689 }
690 gt.cont(jt);
691 }
692 }
693 gt.done(jt);
694 _current_size = table_size(jt);
695 log_debug(symboltable)("Grown to size:" SIZE_FORMAT, _current_size);
696 }
697
698 struct SymbolTableDoDelete : StackObj {
699 int _deleted;
700 SymbolTableDoDelete() : _deleted(0) {}
701 void operator()(Symbol** value) {
702 assert(value != NULL, "expected valid value");
703 assert(*value != NULL, "value should point to a symbol");
704 Symbol *sym = *value;
705 assert(sym->refcount() == 0, "refcount");
706 _deleted++;
707 }
708 };
709
710 struct SymbolTableDeleteCheck : StackObj {
711 int _processed;
712 SymbolTableDeleteCheck() : _processed(0) {}
713 bool operator()(Symbol** value) {
714 assert(value != NULL, "expected valid value");
715 assert(*value != NULL, "value should point to a symbol");
716 _processed++;
717 Symbol *sym = *value;
718 if (sym->refcount() == 0) {
719 return true;
720 } else {
721 return false;
722 }
723 }
724 };
725
726 void SymbolTable::clean_dead_entries(JavaThread* jt) {
727 SymbolTableHash::BulkDeleteTask bdt(_local_table);
728 if (!bdt.prepare(jt)) {
729 return;
730 }
731
732 SymbolTableDeleteCheck stdc;
733 SymbolTableDoDelete stdd;
734 {
735 TraceTime timer("Clean", TRACETIME_LOG(Debug, symboltable, perf));
736 while (bdt.do_task(jt, stdc, stdd)) {
737 bdt.pause(jt);
738 {
739 ThreadBlockInVM tbivm(jt);
740 }
741 bdt.cont(jt);
742 }
743 SymbolTable::the_table()->set_item_clean_count(0);
744 bdt.done(jt);
745 }
746
747 Atomic::add(stdc._processed, &_symbols_counted);
748
749 log_debug(symboltable)("Cleaned " INT32_FORMAT " of " INT32_FORMAT,
750 stdd._deleted, stdc._processed);
751 }
752
753 void SymbolTable::check_concurrent_work() {
754 if (_has_work) {
755 return;
756 }
757 double load_factor = SymbolTable::get_load_factor();
758 double dead_factor = SymbolTable::get_dead_factor();
759 // We should clean/resize if we have more dead than alive,
760 // more items than preferred load factor or
761 // more dead items than water mark.
762 if ((dead_factor > load_factor) ||
763 (load_factor > PREF_AVG_LIST_LEN) ||
764 (dead_factor > CLEAN_DEAD_HIGH_WATER_MARK)) {
765 log_debug(symboltable)("Concurrent work triggered, live factor:%f dead factor:%f",
766 load_factor, dead_factor);
767 trigger_concurrent_work();
768 }
769 }
770
771 void SymbolTable::concurrent_work(JavaThread* jt) {
772 double load_factor = get_load_factor();
773 log_debug(symboltable, perf)("Concurrent work, live factor: %g", load_factor);
774 // We prefer growing, since that also removes dead items
775 if (load_factor > PREF_AVG_LIST_LEN && !_local_table->is_max_size_reached()) {
776 grow(jt);
777 } else {
778 clean_dead_entries(jt);
779 }
780 _has_work = false;
781 }
782
783 class CountDead : StackObj {
784 int _count;
785 public:
786 CountDead() : _count(0) {}
787 bool operator()(Symbol** value) {
788 assert(value != NULL, "expected valid value");
789 assert(*value != NULL, "value should point to a symbol");
790 Symbol* sym = *value;
791 if (sym->refcount() == 0) {
792 _count++;
793 }
794 return true;
795 };
796 int get_dead_count() {
797 return _count;
798 }
799 };
800
801 void SymbolTable::do_check_concurrent_work() {
802 CountDead counter;
803 if (!SymbolTable::the_table()->_local_table->try_scan(Thread::current(), counter)) {
804 log_info(symboltable)("count dead unavailable at this moment");
805 } else {
806 SymbolTable::the_table()->set_item_clean_count(counter.get_dead_count());
807 SymbolTable::the_table()->check_concurrent_work();
808 }
809 }
810
811 void SymbolTable::do_concurrent_work(JavaThread* jt) {
812 SymbolTable::the_table()->concurrent_work(jt);
813 }
814
815 // Rehash
816 bool SymbolTable::do_rehash() {
817 if (!_local_table->is_safepoint_safe()) {
818 return false;
819 }
820
821 // We use max size
822 SymbolTableHash* new_table = new SymbolTableHash(END_SIZE, END_SIZE, REHASH_LEN);
823 // Use alt hash from now on
824 _alt_hash = true;
825 if (!_local_table->try_move_nodes_to(Thread::current(), new_table)) {
826 _alt_hash = false;
827 delete new_table;
828 return false;
829 }
830
831 // free old table
832 delete _local_table;
833 _local_table = new_table;
834
835 return true;
836 }
837
838 void SymbolTable::try_rehash_table() {
839 static bool rehashed = false;
840 log_debug(symboltable)("Table imbalanced, rehashing called.");
841
842 // Grow instead of rehash.
843 if (get_load_factor() > PREF_AVG_LIST_LEN &&
844 !_local_table->is_max_size_reached()) {
845 log_debug(symboltable)("Choosing growing over rehashing.");
846 trigger_concurrent_work();
847 _needs_rehashing = false;
848 return;
849 }
850
851 // Already rehashed.
852 if (rehashed) {
853 log_warning(symboltable)("Rehashing already done, still long lists.");
854 trigger_concurrent_work();
855 _needs_rehashing = false;
856 return;
857 }
858
859 murmur_seed = AltHashing::compute_seed();
860
861 if (do_rehash()) {
862 rehashed = true;
863 } else {
864 log_info(symboltable)("Resizes in progress rehashing skipped.");
865 }
866
867 _needs_rehashing = false;
868 }
869
870 void SymbolTable::rehash_table() {
871 SymbolTable::the_table()->try_rehash_table();
872 }
873
874 //---------------------------------------------------------------------------
875 // Non-product code
876
877 #ifndef PRODUCT
878
879 class HistogramIterator : StackObj {
880 public:
881 static const int results_length = 100;
882 int counts[results_length];
883 int sizes[results_length];
884 int total_size;
885 int total_count;
886 int total_length;
887 int max_length;
888 int out_of_range_count;
889 int out_of_range_size;
890 HistogramIterator() : total_size(0), total_count(0), total_length(0),
891 max_length(0), out_of_range_count(0), out_of_range_size(0) {
892 // initialize results to zero
893 for (int i = 0; i < results_length; i++) {
894 counts[i] = 0;
895 sizes[i] = 0;
896 }
897 }
898 bool operator()(Symbol** value) {
899 assert(value != NULL, "expected valid value");
900 assert(*value != NULL, "value should point to a symbol");
901 Symbol* sym = *value;
902 int size = sym->size();
903 int len = sym->utf8_length();
904 if (len < results_length) {
905 counts[len]++;
906 sizes[len] += size;
907 } else {
908 out_of_range_count++;
909 out_of_range_size += size;
910 }
911 total_count++;
912 total_size += size;
913 total_length += len;
914 max_length = MAX2(max_length, len);
915
916 return true;
917 };
918 };
919
920 void SymbolTable::print_histogram() {
921 HistogramIterator hi;
922 SymbolTable::the_table()->_local_table->do_scan(Thread::current(), hi);
923 tty->print_cr("Symbol Table Histogram:");
924 tty->print_cr(" Total number of symbols %7d", hi.total_count);
925 tty->print_cr(" Total size in memory %7dK",
926 (hi.total_size*wordSize)/1024);
927 tty->print_cr(" Total counted %7d", _symbols_counted);
928 tty->print_cr(" Total removed %7d", _symbols_removed);
929 if (_symbols_counted > 0) {
930 tty->print_cr(" Percent removed %3.2f",
931 ((float)_symbols_removed/(float)_symbols_counted)* 100);
932 }
933 tty->print_cr(" Reference counts %7d", Symbol::_total_count);
934 tty->print_cr(" Symbol arena used " SIZE_FORMAT_W(7) "K", arena()->used()/1024);
935 tty->print_cr(" Symbol arena size " SIZE_FORMAT_W(7) "K", arena()->size_in_bytes()/1024);
936 tty->print_cr(" Total symbol length %7d", hi.total_length);
937 tty->print_cr(" Maximum symbol length %7d", hi.max_length);
938 tty->print_cr(" Average symbol length %7.2f", ((float) hi.total_length / (float) hi.total_count));
939 tty->print_cr(" Symbol length histogram:");
940 tty->print_cr(" %6s %10s %10s", "Length", "#Symbols", "Size");
941 for (int i = 0; i < hi.results_length; i++) {
942 if (hi.counts[i] > 0) {
943 tty->print_cr(" %6d %10d %10dK", i, hi.counts[i], (hi.sizes[i]*wordSize)/1024);
944 }
945 }
946 tty->print_cr(" >=%6d %10d %10dK\n", hi.results_length,
947 hi.out_of_range_count, (hi.out_of_range_size*wordSize)/1024);
948 }
949 #endif // PRODUCT
950
951 // Utility for dumping symbols
952 SymboltableDCmd::SymboltableDCmd(outputStream* output, bool heap) :
953 DCmdWithParser(output, heap),
954 _verbose("-verbose", "Dump the content of each symbol in the table",
955 "BOOLEAN", false, "false") {
956 _dcmdparser.add_dcmd_option(&_verbose);
957 }
958
959 void SymboltableDCmd::execute(DCmdSource source, TRAPS) {
960 VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpSymbols,
961 _verbose.value());
962 VMThread::execute(&dumper);
963 }
964
965 int SymboltableDCmd::num_arguments() {
966 ResourceMark rm;
967 SymboltableDCmd* dcmd = new SymboltableDCmd(NULL, false);
968 if (dcmd != NULL) {
969 DCmdMark mark(dcmd);
970 return dcmd->_dcmdparser.num_arguments();
971 } else {
972 return 0;
973 }
974 }