1 /*
2 * Copyright (c) 1997, 2014, 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/javaClasses.hpp"
28 #include "classfile/stringTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "gc_interface/collectedHeap.inline.hpp"
31 #include "memory/allocation.inline.hpp"
32 #include "memory/filemap.hpp"
33 #include "memory/gcLocker.inline.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "oops/oop.inline2.hpp"
36 #include "runtime/atomic.inline.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "utilities/hashtable.inline.hpp"
39 #if INCLUDE_ALL_GCS
40 #include "gc_implementation/g1/g1SATBCardTableModRefBS.hpp"
41 #include "gc_implementation/g1/g1StringDedup.hpp"
42 #endif
43
44 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
45
46 // the number of buckets a thread claims
47 const int ClaimChunkSize = 32;
48
49 #ifdef ASSERT
50 class StableMemoryChecker : public StackObj {
51 enum { _bufsize = wordSize*4 };
52
53 address _region;
54 jint _size;
55 u1 _save_buf[_bufsize];
56
57 int sample(u1* save_buf) {
58 if (_size <= _bufsize) {
59 memcpy(save_buf, _region, _size);
60 return _size;
61 } else {
62 // copy head and tail
63 memcpy(&save_buf[0], _region, _bufsize/2);
64 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
65 return (_bufsize/2)*2;
66 }
67 }
68
69 public:
70 StableMemoryChecker(const void* region, jint size) {
71 _region = (address) region;
72 _size = size;
73 sample(_save_buf);
74 }
75
76 bool verify() {
77 u1 check_buf[sizeof(_save_buf)];
78 int check_size = sample(check_buf);
79 return (0 == memcmp(_save_buf, check_buf, check_size));
80 }
81
82 void set_region(const void* region) { _region = (address) region; }
83 };
84 #endif
85
86
87 // --------------------------------------------------------------------------
88 StringTable* StringTable::_the_table = NULL;
89
90 bool StringTable::_needs_rehashing = false;
91
92 volatile int StringTable::_parallel_claimed_idx = 0;
93
94 // Pick hashing algorithm
95 unsigned int StringTable::hash_string(const jchar* s, int len) {
96 return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
97 java_lang_String::hash_code(s, len);
98 }
99
100 oop StringTable::lookup(int index, jchar* name,
101 int len, unsigned int hash) {
102 int count = 0;
103 for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
104 count++;
105 if (l->hash() == hash) {
106 if (java_lang_String::equals(l->literal(), name, len)) {
107 return l->literal();
108 }
109 }
110 }
111 // If the bucket size is too deep check if this hash code is insufficient.
112 if (count >= rehash_count && !needs_rehashing()) {
113 _needs_rehashing = check_rehash_table(count);
114 }
115 return NULL;
116 }
117
118
119 oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
120 int len, unsigned int hashValue_arg, TRAPS) {
121
122 assert(java_lang_String::equals(string(), name, len),
123 "string must be properly initialized");
124 // Cannot hit a safepoint in this function because the "this" pointer can move.
125 No_Safepoint_Verifier nsv;
126
127 // Check if the symbol table has been rehashed, if so, need to recalculate
128 // the hash value and index before second lookup.
129 unsigned int hashValue;
130 int index;
131 if (use_alternate_hashcode()) {
132 hashValue = hash_string(name, len);
133 index = hash_to_index(hashValue);
134 } else {
135 hashValue = hashValue_arg;
136 index = index_arg;
137 }
138
139 // Since look-up was done lock-free, we need to check if another
140 // thread beat us in the race to insert the symbol.
141
142 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
143 if (test != NULL) {
144 // Entry already added
145 return test;
146 }
147
148 HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
149 add_entry(index, entry);
150 return string();
151 }
152
153
154 oop StringTable::lookup(Symbol* symbol) {
155 ResourceMark rm;
156 int length;
157 jchar* chars = symbol->as_unicode(length);
158 return lookup(chars, length);
159 }
160
161 // Tell the GC that this string was looked up in the StringTable.
162 static void ensure_string_alive(oop string) {
163 // A lookup in the StringTable could return an object that was previously
164 // considered dead. The SATB part of G1 needs to get notified about this
165 // potential resurrection, otherwise the marking might not find the object.
166 #if INCLUDE_ALL_GCS
167 if (UseG1GC && string != NULL) {
168 G1SATBCardTableModRefBS::enqueue(string);
169 }
170 #endif
171 }
172
173 oop StringTable::lookup(jchar* name, int len) {
174 unsigned int hash = hash_string(name, len);
175 int index = the_table()->hash_to_index(hash);
176 oop string = the_table()->lookup(index, name, len, hash);
177
178 ensure_string_alive(string);
179
180 return string;
181 }
182
183
184 oop StringTable::intern(Handle string_or_null, jchar* name,
185 int len, TRAPS) {
186 unsigned int hashValue = hash_string(name, len);
187 int index = the_table()->hash_to_index(hashValue);
188 oop found_string = the_table()->lookup(index, name, len, hashValue);
189
190 // Found
191 if (found_string != NULL) {
192 ensure_string_alive(found_string);
193 return found_string;
194 }
195
196 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
197 assert(!Universe::heap()->is_in_reserved(name),
198 "proposed name of symbol must be stable");
199
200 Handle string;
201 // try to reuse the string if possible
202 if (!string_or_null.is_null()) {
203 string = string_or_null;
204 } else {
205 string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
206 }
207
208 #if INCLUDE_ALL_GCS
209 if (G1StringDedup::is_enabled()) {
210 // Deduplicate the string before it is interned. Note that we should never
211 // deduplicate a string after it has been interned. Doing so will counteract
212 // compiler optimizations done on e.g. interned string literals.
213 G1StringDedup::deduplicate(string());
214 }
215 #endif
216
217 // Grab the StringTable_lock before getting the_table() because it could
218 // change at safepoint.
219 oop added_or_found;
220 {
221 MutexLocker ml(StringTable_lock, THREAD);
222 // Otherwise, add to symbol to table
223 added_or_found = the_table()->basic_add(index, string, name, len,
224 hashValue, CHECK_NULL);
225 }
226
227 ensure_string_alive(added_or_found);
228
229 return added_or_found;
230 }
231
232 oop StringTable::intern(Symbol* symbol, TRAPS) {
233 if (symbol == NULL) return NULL;
234 ResourceMark rm(THREAD);
235 int length;
236 jchar* chars = symbol->as_unicode(length);
237 Handle string;
238 oop result = intern(string, chars, length, CHECK_NULL);
239 return result;
240 }
241
242
243 oop StringTable::intern(oop string, TRAPS)
244 {
245 if (string == NULL) return NULL;
246 ResourceMark rm(THREAD);
247 int length;
248 Handle h_string (THREAD, string);
249 jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
250 oop result = intern(h_string, chars, length, CHECK_NULL);
251 return result;
252 }
253
254
255 oop StringTable::intern(const char* utf8_string, TRAPS) {
256 if (utf8_string == NULL) return NULL;
257 ResourceMark rm(THREAD);
258 int length = UTF8::unicode_length(utf8_string);
259 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
260 UTF8::convert_to_unicode(utf8_string, chars, length);
261 Handle string;
262 oop result = intern(string, chars, length, CHECK_NULL);
263 return result;
264 }
265
266 void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
267 buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), processed, removed);
268 }
269
270 void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
271 // Readers of the table are unlocked, so we should only be removing
272 // entries at a safepoint.
273 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
274 const int limit = the_table()->table_size();
275
276 for (;;) {
277 // Grab next set of buckets to scan
278 int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
279 if (start_idx >= limit) {
280 // End of table
281 break;
282 }
283
284 int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
285 buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, processed, removed);
286 }
287 }
288
289 void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {
290 const int limit = the_table()->table_size();
291
292 assert(0 <= start_idx && start_idx <= limit,
293 err_msg("start_idx (%d) is out of bounds", start_idx));
294 assert(0 <= end_idx && end_idx <= limit,
295 err_msg("end_idx (%d) is out of bounds", end_idx));
296 assert(start_idx <= end_idx,
297 err_msg("Index ordering: start_idx=%d, end_idx=%d",
298 start_idx, end_idx));
299
300 for (int i = start_idx; i < end_idx; i += 1) {
301 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
302 while (entry != NULL) {
303 assert(!entry->is_shared(), "CDS not used for the StringTable");
304
305 f->do_oop((oop*)entry->literal_addr());
306
307 entry = entry->next();
308 }
309 }
310 }
311
312 void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, int* processed, int* removed) {
313 const int limit = the_table()->table_size();
314
315 assert(0 <= start_idx && start_idx <= limit,
316 err_msg("start_idx (%d) is out of bounds", start_idx));
317 assert(0 <= end_idx && end_idx <= limit,
318 err_msg("end_idx (%d) is out of bounds", end_idx));
319 assert(start_idx <= end_idx,
320 err_msg("Index ordering: start_idx=%d, end_idx=%d",
321 start_idx, end_idx));
322
323 for (int i = start_idx; i < end_idx; ++i) {
324 HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
325 HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
326 while (entry != NULL) {
327 assert(!entry->is_shared(), "CDS not used for the StringTable");
328
329 if (is_alive->do_object_b(entry->literal())) {
330 if (f != NULL) {
331 f->do_oop((oop*)entry->literal_addr());
332 }
333 p = entry->next_addr();
334 } else {
335 *p = entry->next();
336 the_table()->free_entry(entry);
337 (*removed)++;
338 }
339 (*processed)++;
340 entry = *p;
341 }
342 }
343 }
344
345 void StringTable::oops_do(OopClosure* f) {
346 buckets_oops_do(f, 0, the_table()->table_size());
347 }
348
349 void StringTable::possibly_parallel_oops_do(OopClosure* f) {
350 const int limit = the_table()->table_size();
351
352 for (;;) {
353 // Grab next set of buckets to scan
354 int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
355 if (start_idx >= limit) {
356 // End of table
357 break;
358 }
359
360 int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
361 buckets_oops_do(f, start_idx, end_idx);
362 }
363 }
364
365 // This verification is part of Universe::verify() and needs to be quick.
366 // See StringTable::verify_and_compare() below for exhaustive verification.
367 void StringTable::verify() {
368 for (int i = 0; i < the_table()->table_size(); ++i) {
369 HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
370 for ( ; p != NULL; p = p->next()) {
371 oop s = p->literal();
372 guarantee(s != NULL, "interned string is NULL");
373 unsigned int h = java_lang_String::hash_string(s);
374 guarantee(p->hash() == h, "broken hash in string table entry");
375 guarantee(the_table()->hash_to_index(h) == i,
376 "wrong index in string table");
377 }
378 }
379 }
380
381 void StringTable::dump(outputStream* st) {
382 the_table()->dump_table(st, "StringTable");
383 }
384
385 StringTable::VerifyRetTypes StringTable::compare_entries(
386 int bkt1, int e_cnt1,
387 HashtableEntry<oop, mtSymbol>* e_ptr1,
388 int bkt2, int e_cnt2,
389 HashtableEntry<oop, mtSymbol>* e_ptr2) {
390 // These entries are sanity checked by verify_and_compare_entries()
391 // before this function is called.
392 oop str1 = e_ptr1->literal();
393 oop str2 = e_ptr2->literal();
394
395 if (str1 == str2) {
396 tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "
397 "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",
398 (void *)str1, bkt1, e_cnt1, bkt2, e_cnt2);
399 return _verify_fail_continue;
400 }
401
402 if (java_lang_String::equals(str1, str2)) {
403 tty->print_cr("ERROR: identical String values in entry @ "
404 "bucket[%d][%d] and entry @ bucket[%d][%d]",
405 bkt1, e_cnt1, bkt2, e_cnt2);
406 return _verify_fail_continue;
407 }
408
409 return _verify_pass;
410 }
411
412 StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,
413 HashtableEntry<oop, mtSymbol>* e_ptr,
414 StringTable::VerifyMesgModes mesg_mode) {
415
416 VerifyRetTypes ret = _verify_pass; // be optimistic
417
418 oop str = e_ptr->literal();
419 if (str == NULL) {
420 if (mesg_mode == _verify_with_mesgs) {
421 tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,
422 e_cnt);
423 }
424 // NULL oop means no more verifications are possible
425 return _verify_fail_done;
426 }
427
428 if (str->klass() != SystemDictionary::String_klass()) {
429 if (mesg_mode == _verify_with_mesgs) {
430 tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",
431 bkt, e_cnt);
432 }
433 // not a String means no more verifications are possible
434 return _verify_fail_done;
435 }
436
437 unsigned int h = java_lang_String::hash_string(str);
438 if (e_ptr->hash() != h) {
439 if (mesg_mode == _verify_with_mesgs) {
440 tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "
441 "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);
442 }
443 ret = _verify_fail_continue;
444 }
445
446 if (the_table()->hash_to_index(h) != bkt) {
447 if (mesg_mode == _verify_with_mesgs) {
448 tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "
449 "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,
450 the_table()->hash_to_index(h));
451 }
452 ret = _verify_fail_continue;
453 }
454
455 return ret;
456 }
457
458 // See StringTable::verify() above for the quick verification that is
459 // part of Universe::verify(). This verification is exhaustive and
460 // reports on every issue that is found. StringTable::verify() only
461 // reports on the first issue that is found.
462 //
463 // StringTable::verify_entry() checks:
464 // - oop value != NULL (same as verify())
465 // - oop value is a String
466 // - hash(String) == hash in entry (same as verify())
467 // - index for hash == index of entry (same as verify())
468 //
469 // StringTable::compare_entries() checks:
470 // - oops are unique across all entries
471 // - String values are unique across all entries
472 //
473 int StringTable::verify_and_compare_entries() {
474 assert(StringTable_lock->is_locked(), "sanity check");
475
476 int fail_cnt = 0;
477
478 // first, verify all the entries individually:
479 for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {
480 HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);
481 for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {
482 VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);
483 if (ret != _verify_pass) {
484 fail_cnt++;
485 }
486 }
487 }
488
489 // Optimization: if the above check did not find any failures, then
490 // the comparison loop below does not need to call verify_entry()
491 // before calling compare_entries(). If there were failures, then we
492 // have to call verify_entry() to see if the entry can be passed to
493 // compare_entries() safely. When we call verify_entry() in the loop
494 // below, we do so quietly to void duplicate messages and we don't
495 // increment fail_cnt because the failures have already been counted.
496 bool need_entry_verify = (fail_cnt != 0);
497
498 // second, verify all entries relative to each other:
499 for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {
500 HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);
501 for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {
502 if (need_entry_verify) {
503 VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,
504 _verify_quietly);
505 if (ret == _verify_fail_done) {
506 // cannot use the current entry to compare against other entries
507 continue;
508 }
509 }
510
511 for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {
512 HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);
513 int e_cnt2;
514 for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {
515 if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {
516 // skip the entries up to and including the one that
517 // we're comparing against
518 continue;
519 }
520
521 if (need_entry_verify) {
522 VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,
523 _verify_quietly);
524 if (ret == _verify_fail_done) {
525 // cannot compare against this entry
526 continue;
527 }
528 }
529
530 // compare two entries, report and count any failures:
531 if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)
532 != _verify_pass) {
533 fail_cnt++;
534 }
535 }
536 }
537 }
538 }
539 return fail_cnt;
540 }
541
542 // Create a new table and using alternate hash code, populate the new table
543 // with the existing strings. Set flag to use the alternate hash code afterwards.
544 void StringTable::rehash_table() {
545 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
546 // This should never happen with -Xshare:dump but it might in testing mode.
547 if (DumpSharedSpaces) return;
548 StringTable* new_table = new StringTable();
549
550 // Rehash the table
551 the_table()->move_to(new_table);
552
553 // Delete the table and buckets (entries are reused in new table).
554 delete _the_table;
555 // Don't check if we need rehashing until the table gets unbalanced again.
556 // Then rehash with a new global seed.
557 _needs_rehashing = false;
558 _the_table = new_table;
559 }