1 /*
2 * Copyright (c) 1997, 2012, 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.
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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
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23 */
24
25 #ifndef SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP
26 #define SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP
27
28 #include "memory/allocation.inline.hpp"
29 #include "oops/symbol.hpp"
30 #include "utilities/hashtable.hpp"
31
32 // The symbol table holds all Symbol*s and corresponding interned strings.
33 // Symbol*s and literal strings should be canonicalized.
34 //
35 // The interned strings are created lazily.
36 //
37 // It is implemented as an open hash table with a fixed number of buckets.
38 //
39 // %note:
40 // - symbolTableEntrys are allocated in blocks to reduce the space overhead.
41
42 class BoolObjectClosure;
43 class outputStream;
44
45
46 // Class to hold a newly created or referenced Symbol* temporarily in scope.
47 // new_symbol() and lookup() will create a Symbol* if not already in the
48 // symbol table and add to the symbol's reference count.
49 // probe() and lookup_only() will increment the refcount if symbol is found.
50 class TempNewSymbol : public StackObj {
51 Symbol* _temp;
52
53 public:
54 TempNewSymbol() : _temp(NULL) {}
55 // Creating or looking up a symbol increments the symbol's reference count
56 TempNewSymbol(Symbol *s) : _temp(s) {}
57
58 // Operator= increments reference count.
59 void operator=(const TempNewSymbol &s) {
60 //clear(); //FIXME
61 _temp = s._temp;
62 if (_temp !=NULL) _temp->increment_refcount();
63 }
64
65 // Decrement reference counter so it can go away if it's unique
66 void clear() { if (_temp != NULL) _temp->decrement_refcount(); _temp = NULL; }
67
68 ~TempNewSymbol() { clear(); }
69
70 // Operators so they can be used like Symbols
71 Symbol* operator -> () const { return _temp; }
72 bool operator == (Symbol* o) const { return _temp == o; }
73 // Sneaky conversion function
74 operator Symbol*() { return _temp; }
75 };
76
77 class SymbolTable : public Hashtable<Symbol*, mtSymbol> {
78 friend class VMStructs;
79 friend class ClassFileParser;
80
81 private:
82 // The symbol table
83 static SymbolTable* _the_table;
84
85 // Set if one bucket is out of balance due to hash algorithm deficiency
86 static bool _needs_rehashing;
87
88 // For statistics
89 static int symbols_removed;
90 static int symbols_counted;
91
92 Symbol* allocate_symbol(const u1* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F
93
94 // Adding elements
95 Symbol* basic_add(int index, u1* name, int len, unsigned int hashValue,
96 bool c_heap, TRAPS);
97 bool basic_add(ClassLoaderData* loader_data,
98 constantPoolHandle cp, int names_count,
99 const char** names, int* lengths, int* cp_indices,
100 unsigned int* hashValues, TRAPS);
101
102 static void new_symbols(ClassLoaderData* loader_data,
103 constantPoolHandle cp, int names_count,
104 const char** name, int* lengths,
105 int* cp_indices, unsigned int* hashValues,
106 TRAPS) {
107 add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);
108 }
109
110 // Table size
111 enum {
112 symbol_table_size = 20011
113 };
114
115 Symbol* lookup(int index, const char* name, int len, unsigned int hash);
116
117 SymbolTable()
118 : Hashtable<Symbol*, mtSymbol>(symbol_table_size, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}
119
120 SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
121 : Hashtable<Symbol*, mtSymbol>(symbol_table_size, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,
122 number_of_entries) {}
123
124 // Arena for permanent symbols (null class loader) that are never unloaded
125 static Arena* _arena;
126 static Arena* arena() { return _arena; } // called for statistics
127
128 static void initialize_symbols(int arena_alloc_size = 0);
129 public:
130 enum {
131 symbol_alloc_batch_size = 8,
132 // Pick initial size based on java -version size measurements
133 symbol_alloc_arena_size = 360*K
134 };
135
136 // The symbol table
137 static SymbolTable* the_table() { return _the_table; }
138
139 static void create_table() {
140 assert(_the_table == NULL, "One symbol table allowed.");
141 _the_table = new SymbolTable();
142 initialize_symbols(symbol_alloc_arena_size);
143 }
144
145 static void create_table(HashtableBucket<mtSymbol>* t, int length,
146 int number_of_entries) {
147 assert(_the_table == NULL, "One symbol table allowed.");
148 assert(length == symbol_table_size * sizeof(HashtableBucket<mtSymbol>),
149 "bad shared symbol size.");
150 _the_table = new SymbolTable(t, number_of_entries);
151 // if CDS give symbol table a default arena size since most symbols
152 // are already allocated in the shared misc section.
153 initialize_symbols();
154 }
155
156 static unsigned int hash_symbol(const char* s, int len);
157
158 static Symbol* lookup(const char* name, int len, TRAPS);
159 // lookup only, won't add. Also calculate hash.
160 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
161 // Only copy to C string to be added if lookup failed.
162 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
163
164 static void release(Symbol* sym);
165
166 // Look up the address of the literal in the SymbolTable for this Symbol*
167 static Symbol** lookup_symbol_addr(Symbol* sym);
168
169 // jchar (utf16) version of lookups
170 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
171 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
172
173 static void add(ClassLoaderData* loader_data,
174 constantPoolHandle cp, int names_count,
175 const char** names, int* lengths, int* cp_indices,
176 unsigned int* hashValues, TRAPS);
177
178 // Release any dead symbols
179 static void unlink();
180
181 // iterate over symbols
182 static void symbols_do(SymbolClosure *cl);
183
184 // Symbol creation
185 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
186 assert(utf8_buffer != NULL, "just checking");
187 return lookup(utf8_buffer, length, THREAD);
188 }
189 static Symbol* new_symbol(const char* name, TRAPS) {
190 return new_symbol(name, (int)strlen(name), THREAD);
191 }
192 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
193 assert(begin <= end && end <= sym->utf8_length(), "just checking");
194 return lookup(sym, begin, end, THREAD);
195 }
196
197 // Create a symbol in the arena for symbols that are not deleted
198 static Symbol* new_permanent_symbol(const char* name, TRAPS);
199
200 // Symbol lookup
201 static Symbol* lookup(int index, const char* name, int len, TRAPS);
202
203 // Needed for preloading classes in signatures when compiling.
204 // Returns the symbol is already present in symbol table, otherwise
205 // NULL. NO ALLOCATION IS GUARANTEED!
206 static Symbol* probe(const char* name, int len) {
207 unsigned int ignore_hash;
208 return lookup_only(name, len, ignore_hash);
209 }
210 static Symbol* probe_unicode(const jchar* name, int len) {
211 unsigned int ignore_hash;
212 return lookup_only_unicode(name, len, ignore_hash);
213 }
214
215 // Histogram
216 static void print_histogram() PRODUCT_RETURN;
217 static void print() PRODUCT_RETURN;
218
219 // Debugging
220 static void verify();
221 static void dump(outputStream* st);
222
223 // Sharing
224 static void copy_buckets(char** top, char*end) {
225 the_table()->Hashtable<Symbol*, mtSymbol>::copy_buckets(top, end);
226 }
227 static void copy_table(char** top, char*end) {
228 the_table()->Hashtable<Symbol*, mtSymbol>::copy_table(top, end);
229 }
230 static void reverse(void* boundary = NULL) {
231 the_table()->Hashtable<Symbol*, mtSymbol>::reverse(boundary);
232 }
233
234 // Rehash the symbol table if it gets out of balance
235 static void rehash_table();
236 static bool needs_rehashing() { return _needs_rehashing; }
237 };
238
239 class StringTable : public Hashtable<oop, mtSymbol> {
240 friend class VMStructs;
241
242 private:
243 // The string table
244 static StringTable* _the_table;
245
246 // Set if one bucket is out of balance due to hash algorithm deficiency
247 static bool _needs_rehashing;
248
249 static oop intern(Handle string_or_null, jchar* chars, int length, TRAPS);
250 oop basic_add(int index, Handle string_or_null, jchar* name, int len,
251 unsigned int hashValue, TRAPS);
252
253 oop lookup(int index, jchar* chars, int length, unsigned int hashValue);
254
255 StringTable() : Hashtable<oop, mtSymbol>((int)StringTableSize,
256 sizeof (HashtableEntry<oop, mtSymbol>)) {}
257
258 StringTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
259 : Hashtable<oop, mtSymbol>((int)StringTableSize, sizeof (HashtableEntry<oop, mtSymbol>), t,
260 number_of_entries) {}
261 public:
262 // The string table
263 static StringTable* the_table() { return _the_table; }
264
265 // Size of one bucket in the string table. Used when checking for rollover.
266 static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
267
268 static void create_table() {
269 assert(_the_table == NULL, "One string table allowed.");
270 _the_table = new StringTable();
271 }
272
273 // GC support
274 // Delete pointers to otherwise-unreachable objects.
275 static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f);
276 static void unlink(BoolObjectClosure* cl) {
277 unlink_or_oops_do(cl, NULL);
278 }
279
280 // Invoke "f->do_oop" on the locations of all oops in the table.
281 static void oops_do(OopClosure* f);
282
283 // Hashing algorithm, used as the hash value used by the
284 // StringTable for bucket selection and comparison (stored in the
285 // HashtableEntry structures). This is used in the String.intern() method.
286 static unsigned int hash_string(const jchar* s, int len);
287
288 // Internal test.
289 static void test_alt_hash() PRODUCT_RETURN;
290
291 // Probing
292 static oop lookup(Symbol* symbol);
293 static oop lookup(jchar* chars, int length);
294
295 // Interning
296 static oop intern(Symbol* symbol, TRAPS);
297 static oop intern(oop string, TRAPS);
298 static oop intern(const char *utf8_string, TRAPS);
299
300 // Debugging
301 static void verify();
302 static void dump(outputStream* st);
303
304 // Sharing
305 static void copy_buckets(char** top, char*end) {
306 the_table()->Hashtable<oop, mtSymbol>::copy_buckets(top, end);
307 }
308 static void copy_table(char** top, char*end) {
309 the_table()->Hashtable<oop, mtSymbol>::copy_table(top, end);
310 }
311 static void reverse() {
312 the_table()->Hashtable<oop, mtSymbol>::reverse();
313 }
314
315 // Rehash the symbol table if it gets out of balance
316 static void rehash_table();
317 static bool needs_rehashing() { return _needs_rehashing; }
318 };
319 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP