1 /*
2 * Copyright (c) 1997, 2009, 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 "incls/_precompiled.incl"
26 # include "incls/_symbolTable.cpp.incl"
27
28 // --------------------------------------------------------------------------
29
30 SymbolTable* SymbolTable::_the_table = NULL;
31
32 // Lookup a symbol in a bucket.
33
34 symbolOop SymbolTable::lookup(int index, const char* name,
35 int len, unsigned int hash) {
36 for (HashtableEntry* e = bucket(index); e != NULL; e = e->next()) {
37 if (e->hash() == hash) {
38 symbolOop sym = symbolOop(e->literal());
39 if (sym->equals(name, len)) {
40 return sym;
41 }
42 }
43 }
44 return NULL;
45 }
46
47
48 // We take care not to be blocking while holding the
49 // SymbolTable_lock. Otherwise, the system might deadlock, since the
50 // symboltable is used during compilation (VM_thread) The lock free
51 // synchronization is simplified by the fact that we do not delete
52 // entries in the symbol table during normal execution (only during
53 // safepoints).
54
55 symbolOop SymbolTable::lookup(const char* name, int len, TRAPS) {
56 unsigned int hashValue = hash_symbol(name, len);
57 int index = the_table()->hash_to_index(hashValue);
58
59 symbolOop s = the_table()->lookup(index, name, len, hashValue);
60
61 // Found
62 if (s != NULL) return s;
63
64 // Otherwise, add to symbol to table
65 return the_table()->basic_add(index, (u1*)name, len, hashValue, CHECK_NULL);
66 }
67
68 symbolOop SymbolTable::lookup(symbolHandle sym, int begin, int end, TRAPS) {
69 char* buffer;
70 int index, len;
71 unsigned int hashValue;
72 char* name;
73 {
74 debug_only(No_Safepoint_Verifier nsv;)
75
76 name = (char*)sym->base() + begin;
77 len = end - begin;
78 hashValue = hash_symbol(name, len);
79 index = the_table()->hash_to_index(hashValue);
80 symbolOop s = the_table()->lookup(index, name, len, hashValue);
81
82 // Found
83 if (s != NULL) return s;
84 }
85
86 // Otherwise, add to symbol to table. Copy to a C string first.
87 char stack_buf[128];
88 ResourceMark rm(THREAD);
89 if (len <= 128) {
90 buffer = stack_buf;
91 } else {
92 buffer = NEW_RESOURCE_ARRAY_IN_THREAD(THREAD, char, len);
93 }
94 for (int i=0; i<len; i++) {
95 buffer[i] = name[i];
96 }
97 // Make sure there is no safepoint in the code above since name can't move.
98 // We can't include the code in No_Safepoint_Verifier because of the
99 // ResourceMark.
100
101 return the_table()->basic_add(index, (u1*)buffer, len, hashValue, CHECK_NULL);
102 }
103
104 symbolOop SymbolTable::lookup_only(const char* name, int len,
105 unsigned int& hash) {
106 hash = hash_symbol(name, len);
107 int index = the_table()->hash_to_index(hash);
108
109 return the_table()->lookup(index, name, len, hash);
110 }
111
112 // Suggestion: Push unicode-based lookup all the way into the hashing
113 // and probing logic, so there is no need for convert_to_utf8 until
114 // an actual new symbolOop is created.
115 symbolOop SymbolTable::lookup_unicode(const jchar* name, int utf16_length, TRAPS) {
116 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
117 char stack_buf[128];
118 if (utf8_length < (int) sizeof(stack_buf)) {
119 char* chars = stack_buf;
120 UNICODE::convert_to_utf8(name, utf16_length, chars);
121 return lookup(chars, utf8_length, THREAD);
122 } else {
123 ResourceMark rm(THREAD);
124 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
125 UNICODE::convert_to_utf8(name, utf16_length, chars);
126 return lookup(chars, utf8_length, THREAD);
127 }
128 }
129
130 symbolOop SymbolTable::lookup_only_unicode(const jchar* name, int utf16_length,
131 unsigned int& hash) {
132 int utf8_length = UNICODE::utf8_length((jchar*) name, utf16_length);
133 char stack_buf[128];
134 if (utf8_length < (int) sizeof(stack_buf)) {
135 char* chars = stack_buf;
136 UNICODE::convert_to_utf8(name, utf16_length, chars);
137 return lookup_only(chars, utf8_length, hash);
138 } else {
139 ResourceMark rm;
140 char* chars = NEW_RESOURCE_ARRAY(char, utf8_length + 1);;
141 UNICODE::convert_to_utf8(name, utf16_length, chars);
142 return lookup_only(chars, utf8_length, hash);
143 }
144 }
145
146 void SymbolTable::add(constantPoolHandle cp, int names_count,
147 const char** names, int* lengths, int* cp_indices,
148 unsigned int* hashValues, TRAPS) {
149 SymbolTable* table = the_table();
150 bool added = table->basic_add(cp, names_count, names, lengths,
151 cp_indices, hashValues, CHECK);
152 if (!added) {
153 // do it the hard way
154 for (int i=0; i<names_count; i++) {
155 int index = table->hash_to_index(hashValues[i]);
156 symbolOop sym = table->basic_add(index, (u1*)names[i], lengths[i],
157 hashValues[i], CHECK);
158 cp->symbol_at_put(cp_indices[i], sym);
159 }
160 }
161 }
162
163 symbolOop SymbolTable::basic_add(int index, u1 *name, int len,
164 unsigned int hashValue, TRAPS) {
165 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
166 "proposed name of symbol must be stable");
167
168 // We assume that lookup() has been called already, that it failed,
169 // and symbol was not found. We create the symbol here.
170 symbolKlass* sk = (symbolKlass*) Universe::symbolKlassObj()->klass_part();
171 symbolOop s_oop = sk->allocate_symbol(name, len, CHECK_NULL);
172 symbolHandle sym (THREAD, s_oop);
173
174 // Allocation must be done before grapping the SymbolTable_lock lock
175 MutexLocker ml(SymbolTable_lock, THREAD);
176
177 assert(sym->equals((char*)name, len), "symbol must be properly initialized");
178
179 // Since look-up was done lock-free, we need to check if another
180 // thread beat us in the race to insert the symbol.
181
182 symbolOop test = lookup(index, (char*)name, len, hashValue);
183 if (test != NULL) {
184 // A race occurred and another thread introduced the symbol, this one
185 // will be dropped and collected.
186 return test;
187 }
188
189 HashtableEntry* entry = new_entry(hashValue, sym());
190 add_entry(index, entry);
191 return sym();
192 }
193
194 bool SymbolTable::basic_add(constantPoolHandle cp, int names_count,
195 const char** names, int* lengths,
196 int* cp_indices, unsigned int* hashValues,
197 TRAPS) {
198 symbolKlass* sk = (symbolKlass*) Universe::symbolKlassObj()->klass_part();
199 symbolOop sym_oops[symbol_alloc_batch_size];
200 bool allocated = sk->allocate_symbols(names_count, names, lengths,
201 sym_oops, CHECK_false);
202 if (!allocated) {
203 return false;
204 }
205 symbolHandle syms[symbol_alloc_batch_size];
206 int i;
207 for (i=0; i<names_count; i++) {
208 syms[i] = symbolHandle(THREAD, sym_oops[i]);
209 }
210
211 // Allocation must be done before grabbing the SymbolTable_lock lock
212 MutexLocker ml(SymbolTable_lock, THREAD);
213
214 for (i=0; i<names_count; i++) {
215 assert(syms[i]->equals(names[i], lengths[i]), "symbol must be properly initialized");
216 // Since look-up was done lock-free, we need to check if another
217 // thread beat us in the race to insert the symbol.
218 int index = hash_to_index(hashValues[i]);
219 symbolOop test = lookup(index, names[i], lengths[i], hashValues[i]);
220 if (test != NULL) {
221 // A race occurred and another thread introduced the symbol, this one
222 // will be dropped and collected. Use test instead.
223 cp->symbol_at_put(cp_indices[i], test);
224 } else {
225 symbolOop sym = syms[i]();
226 HashtableEntry* entry = new_entry(hashValues[i], sym);
227 add_entry(index, entry);
228 cp->symbol_at_put(cp_indices[i], sym);
229 }
230 }
231
232 return true;
233 }
234
235
236 void SymbolTable::verify() {
237 for (int i = 0; i < the_table()->table_size(); ++i) {
238 HashtableEntry* p = the_table()->bucket(i);
239 for ( ; p != NULL; p = p->next()) {
240 symbolOop s = symbolOop(p->literal());
241 guarantee(s != NULL, "symbol is NULL");
242 s->verify();
243 guarantee(s->is_perm(), "symbol not in permspace");
244 unsigned int h = hash_symbol((char*)s->bytes(), s->utf8_length());
245 guarantee(p->hash() == h, "broken hash in symbol table entry");
246 guarantee(the_table()->hash_to_index(h) == i,
247 "wrong index in symbol table");
248 }
249 }
250 }
251
252
253 //---------------------------------------------------------------------------
254 // Non-product code
255
256 #ifndef PRODUCT
257
258 void SymbolTable::print_histogram() {
259 MutexLocker ml(SymbolTable_lock);
260 const int results_length = 100;
261 int results[results_length];
262 int i,j;
263
264 // initialize results to zero
265 for (j = 0; j < results_length; j++) {
266 results[j] = 0;
267 }
268
269 int total = 0;
270 int max_symbols = 0;
271 int out_of_range = 0;
272 for (i = 0; i < the_table()->table_size(); i++) {
273 HashtableEntry* p = the_table()->bucket(i);
274 for ( ; p != NULL; p = p->next()) {
275 int counter = symbolOop(p->literal())->utf8_length();
276 total += counter;
277 if (counter < results_length) {
278 results[counter]++;
279 } else {
280 out_of_range++;
281 }
282 max_symbols = MAX2(max_symbols, counter);
283 }
284 }
285 tty->print_cr("Symbol Table:");
286 tty->print_cr("%8s %5d", "Total ", total);
287 tty->print_cr("%8s %5d", "Maximum", max_symbols);
288 tty->print_cr("%8s %3.2f", "Average",
289 ((float) total / (float) the_table()->table_size()));
290 tty->print_cr("%s", "Histogram:");
291 tty->print_cr(" %s %29s", "Length", "Number chains that length");
292 for (i = 0; i < results_length; i++) {
293 if (results[i] > 0) {
294 tty->print_cr("%6d %10d", i, results[i]);
295 }
296 }
297 int line_length = 70;
298 tty->print_cr("%s %30s", " Length", "Number chains that length");
299 for (i = 0; i < results_length; i++) {
300 if (results[i] > 0) {
301 tty->print("%4d", i);
302 for (j = 0; (j < results[i]) && (j < line_length); j++) {
303 tty->print("%1s", "*");
304 }
305 if (j == line_length) {
306 tty->print("%1s", "+");
307 }
308 tty->cr();
309 }
310 }
311 tty->print_cr(" %s %d: %d\n", "Number chains longer than",
312 results_length, out_of_range);
313 }
314
315 #endif // PRODUCT
316
317 // --------------------------------------------------------------------------
318
319 #ifdef ASSERT
320 class StableMemoryChecker : public StackObj {
321 enum { _bufsize = wordSize*4 };
322
323 address _region;
324 jint _size;
325 u1 _save_buf[_bufsize];
326
327 int sample(u1* save_buf) {
328 if (_size <= _bufsize) {
329 memcpy(save_buf, _region, _size);
330 return _size;
331 } else {
332 // copy head and tail
333 memcpy(&save_buf[0], _region, _bufsize/2);
334 memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
335 return (_bufsize/2)*2;
336 }
337 }
338
339 public:
340 StableMemoryChecker(const void* region, jint size) {
341 _region = (address) region;
342 _size = size;
343 sample(_save_buf);
344 }
345
346 bool verify() {
347 u1 check_buf[sizeof(_save_buf)];
348 int check_size = sample(check_buf);
349 return (0 == memcmp(_save_buf, check_buf, check_size));
350 }
351
352 void set_region(const void* region) { _region = (address) region; }
353 };
354 #endif
355
356
357 // --------------------------------------------------------------------------
358
359
360 // Compute the hash value for a java.lang.String object which would
361 // contain the characters passed in. This hash value is used for at
362 // least two purposes.
363 //
364 // (a) As the hash value used by the StringTable for bucket selection
365 // and comparison (stored in the HashtableEntry structures). This
366 // is used in the String.intern() method.
367 //
368 // (b) As the hash value used by the String object itself, in
369 // String.hashCode(). This value is normally calculate in Java code
370 // in the String.hashCode method(), but is precomputed for String
371 // objects in the shared archive file.
372 //
373 // For this reason, THIS ALGORITHM MUST MATCH String.hashCode().
374
375 int StringTable::hash_string(jchar* s, int len) {
376 unsigned h = 0;
377 while (len-- > 0) {
378 h = 31*h + (unsigned) *s;
379 s++;
380 }
381 return h;
382 }
383
384
385 StringTable* StringTable::_the_table = NULL;
386
387 oop StringTable::lookup(int index, jchar* name,
388 int len, unsigned int hash) {
389 for (HashtableEntry* l = bucket(index); l != NULL; l = l->next()) {
390 if (l->hash() == hash) {
391 if (java_lang_String::equals(l->literal(), name, len)) {
392 return l->literal();
393 }
394 }
395 }
396 return NULL;
397 }
398
399
400 oop StringTable::basic_add(int index, Handle string_or_null, jchar* name,
401 int len, unsigned int hashValue, TRAPS) {
402 debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
403 assert(!Universe::heap()->is_in_reserved(name) || GC_locker::is_active(),
404 "proposed name of symbol must be stable");
405
406 Handle string;
407 // try to reuse the string if possible
408 if (!string_or_null.is_null() && string_or_null()->is_perm()) {
409 string = string_or_null;
410 } else {
411 string = java_lang_String::create_tenured_from_unicode(name, len, CHECK_NULL);
412 }
413
414 // Allocation must be done before grapping the SymbolTable_lock lock
415 MutexLocker ml(StringTable_lock, THREAD);
416
417 assert(java_lang_String::equals(string(), name, len),
418 "string must be properly initialized");
419
420 // Since look-up was done lock-free, we need to check if another
421 // thread beat us in the race to insert the symbol.
422
423 oop test = lookup(index, name, len, hashValue); // calls lookup(u1*, int)
424 if (test != NULL) {
425 // Entry already added
426 return test;
427 }
428
429 HashtableEntry* entry = new_entry(hashValue, string());
430 add_entry(index, entry);
431 return string();
432 }
433
434
435 oop StringTable::lookup(symbolOop symbol) {
436 ResourceMark rm;
437 int length;
438 jchar* chars = symbol->as_unicode(length);
439 unsigned int hashValue = hash_string(chars, length);
440 int index = the_table()->hash_to_index(hashValue);
441 return the_table()->lookup(index, chars, length, hashValue);
442 }
443
444
445 oop StringTable::intern(Handle string_or_null, jchar* name,
446 int len, TRAPS) {
447 unsigned int hashValue = hash_string(name, len);
448 int index = the_table()->hash_to_index(hashValue);
449 oop string = the_table()->lookup(index, name, len, hashValue);
450
451 // Found
452 if (string != NULL) return string;
453
454 // Otherwise, add to symbol to table
455 return the_table()->basic_add(index, string_or_null, name, len,
456 hashValue, CHECK_NULL);
457 }
458
459 oop StringTable::intern(symbolOop symbol, TRAPS) {
460 if (symbol == NULL) return NULL;
461 ResourceMark rm(THREAD);
462 int length;
463 jchar* chars = symbol->as_unicode(length);
464 Handle string;
465 oop result = intern(string, chars, length, CHECK_NULL);
466 return result;
467 }
468
469
470 oop StringTable::intern(oop string, TRAPS)
471 {
472 if (string == NULL) return NULL;
473 ResourceMark rm(THREAD);
474 int length;
475 Handle h_string (THREAD, string);
476 jchar* chars = java_lang_String::as_unicode_string(string, length);
477 oop result = intern(h_string, chars, length, CHECK_NULL);
478 return result;
479 }
480
481
482 oop StringTable::intern(const char* utf8_string, TRAPS) {
483 if (utf8_string == NULL) return NULL;
484 ResourceMark rm(THREAD);
485 int length = UTF8::unicode_length(utf8_string);
486 jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
487 UTF8::convert_to_unicode(utf8_string, chars, length);
488 Handle string;
489 oop result = intern(string, chars, length, CHECK_NULL);
490 return result;
491 }
492
493 void StringTable::verify() {
494 for (int i = 0; i < the_table()->table_size(); ++i) {
495 HashtableEntry* p = the_table()->bucket(i);
496 for ( ; p != NULL; p = p->next()) {
497 oop s = p->literal();
498 guarantee(s != NULL, "interned string is NULL");
499 guarantee(s->is_perm(), "interned string not in permspace");
500
501 int length;
502 jchar* chars = java_lang_String::as_unicode_string(s, length);
503 unsigned int h = hash_string(chars, length);
504 guarantee(p->hash() == h, "broken hash in string table entry");
505 guarantee(the_table()->hash_to_index(h) == i,
506 "wrong index in string table");
507 }
508 }
509 }