1 /*
2 * Copyright (c) 1997, 2017, 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
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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 RehashableHashtable<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 Symbol* lookup(int index, const char* name, int len, unsigned int hash);
111
112 SymbolTable()
113 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}
114
115 SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
116 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,
117 number_of_entries) {}
118
119 // Arena for permanent symbols (null class loader) that are never unloaded
120 static Arena* _arena;
121 static Arena* arena() { return _arena; } // called for statistics
122
123 static void initialize_symbols(int arena_alloc_size = 0);
124
125 static volatile int _parallel_claimed_idx;
126
127 typedef SymbolTable::BucketUnlinkContext BucketUnlinkContext;
128 // Release any dead symbols. Unlinked bucket entries are collected in the given
129 // context to be freed later.
130 // This allows multiple threads to work on the table at once.
131 static void buckets_unlink(int start_idx, int end_idx, BucketUnlinkContext* context, size_t* memory_total);
132 public:
133 enum {
134 symbol_alloc_batch_size = 8,
135 // Pick initial size based on java -version size measurements
136 symbol_alloc_arena_size = 360*K
137 };
138
139 // The symbol table
140 static SymbolTable* the_table() { return _the_table; }
141
142 // Size of one bucket in the string table. Used when checking for rollover.
143 static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
144
145 static void create_table() {
146 assert(_the_table == NULL, "One symbol table allowed.");
147 _the_table = new SymbolTable();
148 initialize_symbols(symbol_alloc_arena_size);
149 }
150
151 static void create_table(HashtableBucket<mtSymbol>* t, int length,
152 int number_of_entries) {
153 assert(_the_table == NULL, "One symbol table allowed.");
154
155 // If CDS archive used a different symbol table size, use that size instead
156 // which is better than giving an error.
157 SymbolTableSize = length/bucket_size();
158
159 _the_table = new SymbolTable(t, number_of_entries);
160 // if CDS give symbol table a default arena size since most symbols
161 // are already allocated in the shared misc section.
162 initialize_symbols();
163 }
164
165 static unsigned int hash_symbol(const char* s, int len);
166
167 static Symbol* lookup(const char* name, int len, TRAPS);
168 // lookup only, won't add. Also calculate hash.
169 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
170 // Only copy to C string to be added if lookup failed.
171 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
172
173 static void release(Symbol* sym);
174
175 // Look up the address of the literal in the SymbolTable for this Symbol*
176 static Symbol** lookup_symbol_addr(Symbol* sym);
177
178 // jchar (utf16) version of lookups
179 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
180 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
181
182 static void add(ClassLoaderData* loader_data,
183 constantPoolHandle cp, int names_count,
184 const char** names, int* lengths, int* cp_indices,
185 unsigned int* hashValues, TRAPS);
186
187 // Release any dead symbols
188 static void unlink() {
189 int processed = 0;
190 int removed = 0;
191 unlink(&processed, &removed);
192 }
193 static void unlink(int* processed, int* removed);
194 // Release any dead symbols, possibly parallel version
195 static void possibly_parallel_unlink(int* processed, int* removed);
196
197 // iterate over symbols
198 static void symbols_do(SymbolClosure *cl);
199
200 // Symbol creation
201 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
202 assert(utf8_buffer != NULL, "just checking");
203 return lookup(utf8_buffer, length, THREAD);
204 }
205 static Symbol* new_symbol(const char* name, TRAPS) {
206 return new_symbol(name, (int)strlen(name), THREAD);
207 }
208 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
209 assert(begin <= end && end <= sym->utf8_length(), "just checking");
210 return lookup(sym, begin, end, THREAD);
211 }
212
213 // Create a symbol in the arena for symbols that are not deleted
214 static Symbol* new_permanent_symbol(const char* name, TRAPS);
215
216 // Symbol lookup
217 static Symbol* lookup(int index, const char* name, int len, TRAPS);
218
219 // Needed for preloading classes in signatures when compiling.
220 // Returns the symbol is already present in symbol table, otherwise
221 // NULL. NO ALLOCATION IS GUARANTEED!
222 static Symbol* probe(const char* name, int len) {
223 unsigned int ignore_hash;
224 return lookup_only(name, len, ignore_hash);
225 }
226 static Symbol* probe_unicode(const jchar* name, int len) {
227 unsigned int ignore_hash;
228 return lookup_only_unicode(name, len, ignore_hash);
229 }
230
231 // Histogram
232 static void print_histogram() PRODUCT_RETURN;
233 static void print() PRODUCT_RETURN;
234
235 // Debugging
236 static void verify();
237 static void dump(outputStream* st);
238
239 // Sharing
240 static void copy_buckets(char** top, char*end) {
241 the_table()->Hashtable<Symbol*, mtSymbol>::copy_buckets(top, end);
242 }
243 static void copy_table(char** top, char*end) {
244 the_table()->Hashtable<Symbol*, mtSymbol>::copy_table(top, end);
245 }
246 static void reverse(void* boundary = NULL) {
247 the_table()->Hashtable<Symbol*, mtSymbol>::reverse(boundary);
248 }
249
250 // Rehash the symbol table if it gets out of balance
251 static void rehash_table();
252 static bool needs_rehashing() { return _needs_rehashing; }
253 // Parallel chunked scanning
254 static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
255 static int parallel_claimed_index() { return _parallel_claimed_idx; }
256 };
257
258 class StringTable : public RehashableHashtable<oop, mtSymbol> {
259 friend class VMStructs;
260
261 private:
262 // The string table
263 static StringTable* _the_table;
264
265 // Set if one bucket is out of balance due to hash algorithm deficiency
266 static bool _needs_rehashing;
267
268 // Claimed high water mark for parallel chunked scanning
269 static volatile int _parallel_claimed_idx;
270
271 static oop intern(Handle string_or_null, jchar* chars, int length, TRAPS);
272 oop basic_add(int index, Handle string_or_null, jchar* name, int len,
273 unsigned int hashValue, TRAPS);
274
275 oop lookup(int index, jchar* chars, int length, unsigned int hashValue);
276
277 // Apply the give oop closure to the entries to the buckets
278 // in the range [start_idx, end_idx).
279 static void buckets_oops_do(OopClosure* f, int start_idx, int end_idx);
280
281 typedef StringTable::BucketUnlinkContext BucketUnlinkContext;
282 // Unlink or apply the give oop closure to the entries to the buckets
283 // in the range [start_idx, end_idx). Unlinked bucket entries are collected in the given
284 // context to be freed later.
285 // This allows multiple threads to work on the table at once.
286 static void buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context);
287
288 StringTable() : RehashableHashtable<oop, mtSymbol>((int)StringTableSize,
289 sizeof (HashtableEntry<oop, mtSymbol>)) {}
290
291 StringTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
292 : RehashableHashtable<oop, mtSymbol>((int)StringTableSize, sizeof (HashtableEntry<oop, mtSymbol>), t,
293 number_of_entries) {}
294 public:
295 // The string table
296 static StringTable* the_table() { return _the_table; }
297
298 // Size of one bucket in the string table. Used when checking for rollover.
299 static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
300
301 static void create_table() {
302 assert(_the_table == NULL, "One string table allowed.");
303 _the_table = new StringTable();
304 }
305
306 // GC support
307 // Delete pointers to otherwise-unreachable objects.
308 static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f) {
309 int processed = 0;
310 int removed = 0;
311 unlink_or_oops_do(cl, f, &processed, &removed);
312 }
313 static void unlink(BoolObjectClosure* cl) {
314 int processed = 0;
315 int removed = 0;
316 unlink_or_oops_do(cl, NULL, &processed, &removed);
317 }
318 static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
319 static void unlink(BoolObjectClosure* cl, int* processed, int* removed) {
320 unlink_or_oops_do(cl, NULL, processed, removed);
321 }
322 // Serially invoke "f->do_oop" on the locations of all oops in the table.
323 static void oops_do(OopClosure* f);
324
325 // Possibly parallel versions of the above
326 static void possibly_parallel_unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
327 static void possibly_parallel_unlink(BoolObjectClosure* cl, int* processed, int* removed) {
328 possibly_parallel_unlink_or_oops_do(cl, NULL, processed, removed);
329 }
330 static void possibly_parallel_oops_do(OopClosure* f);
331
332 // Hashing algorithm, used as the hash value used by the
333 // StringTable for bucket selection and comparison (stored in the
334 // HashtableEntry structures). This is used in the String.intern() method.
335 static unsigned int hash_string(const jchar* s, int len);
336
337 // Internal test.
338 static void test_alt_hash() PRODUCT_RETURN;
339
340 // Probing
341 static oop lookup(Symbol* symbol);
342 static oop lookup(jchar* chars, int length);
343
344 // Interning
345 static oop intern(Symbol* symbol, TRAPS);
346 static oop intern(oop string, TRAPS);
347 static oop intern(const char *utf8_string, TRAPS);
348
349 // Debugging
350 static void verify();
351 static void dump(outputStream* st);
352
353 enum VerifyMesgModes {
354 _verify_quietly = 0,
355 _verify_with_mesgs = 1
356 };
357
358 enum VerifyRetTypes {
359 _verify_pass = 0,
360 _verify_fail_continue = 1,
361 _verify_fail_done = 2
362 };
363
364 static VerifyRetTypes compare_entries(int bkt1, int e_cnt1,
365 HashtableEntry<oop, mtSymbol>* e_ptr1,
366 int bkt2, int e_cnt2,
367 HashtableEntry<oop, mtSymbol>* e_ptr2);
368 static VerifyRetTypes verify_entry(int bkt, int e_cnt,
369 HashtableEntry<oop, mtSymbol>* e_ptr,
370 VerifyMesgModes mesg_mode);
371 static int verify_and_compare_entries();
372
373 // Sharing
374 static void copy_buckets(char** top, char*end) {
375 the_table()->Hashtable<oop, mtSymbol>::copy_buckets(top, end);
376 }
377 static void copy_table(char** top, char*end) {
378 the_table()->Hashtable<oop, mtSymbol>::copy_table(top, end);
379 }
380 static void reverse() {
381 the_table()->Hashtable<oop, mtSymbol>::reverse();
382 }
383
384 // Rehash the symbol table if it gets out of balance
385 static void rehash_table();
386 static bool needs_rehashing() { return _needs_rehashing; }
387
388 // Parallel chunked scanning
389 static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
390 static int parallel_claimed_index() { return _parallel_claimed_idx; }
391 };
392 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP