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.
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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.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 class SerializeClosure;
45
46 // TempNewSymbol acts as a handle class in a handle/body idiom and is
47 // responsible for proper resource management of the body (which is a Symbol*).
48 // The body is resource managed by a reference counting scheme.
49 // TempNewSymbol can therefore be used to properly hold a newly created or referenced
50 // Symbol* temporarily in scope.
51 //
52 // Routines in SymbolTable will initialize the reference count of a Symbol* before
53 // it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol
54 // needs to maintain proper reference counting in context of copy semantics.
55 //
56 // In SymbolTable, new_symbol() and lookup() will create a Symbol* if not already in the
57 // symbol table and add to the symbol's reference count.
58 // probe() and lookup_only() will increment the refcount if symbol is found.
59 class TempNewSymbol : public StackObj {
60 Symbol* _temp;
61
62 public:
63 TempNewSymbol() : _temp(NULL) {}
64
65 // Conversion from a Symbol* to a TempNewSymbol.
66 // Does not increment the current reference count.
67 TempNewSymbol(Symbol *s) : _temp(s) {}
68
69 // Copy constructor increments reference count.
70 TempNewSymbol(const TempNewSymbol& rhs) : _temp(rhs._temp) {
71 if (_temp != NULL) {
72 _temp->increment_refcount();
73 }
74 }
75
76 // Assignment operator uses a c++ trick called copy and swap idiom.
77 // rhs is passed by value so within the scope of this method it is a copy.
78 // At method exit it contains the former value of _temp, triggering the correct refcount
79 // decrement upon destruction.
80 void operator=(TempNewSymbol rhs) {
81 Symbol* tmp = rhs._temp;
82 rhs._temp = _temp;
83 _temp = tmp;
84 }
85
86 // Decrement reference counter so it can go away if it's unused
87 ~TempNewSymbol() {
88 if (_temp != NULL) {
89 _temp->decrement_refcount();
90 }
91 }
92
93 // Symbol* conversion operators
94 Symbol* operator -> () const { return _temp; }
95 bool operator == (Symbol* o) const { return _temp == o; }
96 operator Symbol*() { return _temp; }
97 };
98
99 template <class T, class N> class CompactHashtable;
100
101 class SymbolTable : public RehashableHashtable<Symbol*, mtSymbol> {
102 friend class VMStructs;
103 friend class ClassFileParser;
104
105 private:
106 // The symbol table
107 static SymbolTable* _the_table;
108
109 // Set if one bucket is out of balance due to hash algorithm deficiency
110 static bool _needs_rehashing;
111 static bool _lookup_shared_first;
112
113 // For statistics
114 static int _symbols_removed;
115 static int _symbols_counted;
116
117 // shared symbol table.
118 static CompactHashtable<Symbol*, char> _shared_table;
119
120 Symbol* allocate_symbol(const u1* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F
121
122 // Adding elements
123 Symbol* basic_add(int index, u1* name, int len, unsigned int hashValue,
124 bool c_heap, TRAPS);
125 bool basic_add(ClassLoaderData* loader_data,
126 const constantPoolHandle& cp, int names_count,
127 const char** names, int* lengths, int* cp_indices,
128 unsigned int* hashValues, TRAPS);
129
130 static void new_symbols(ClassLoaderData* loader_data,
131 const constantPoolHandle& cp, int names_count,
132 const char** name, int* lengths,
133 int* cp_indices, unsigned int* hashValues,
134 TRAPS) {
135 add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);
136 }
137
138 static Symbol* lookup_shared(const char* name, int len, unsigned int hash);
139 Symbol* lookup_dynamic(int index, const char* name, int len, unsigned int hash);
140 Symbol* lookup(int index, const char* name, int len, unsigned int hash);
141
142 SymbolTable()
143 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}
144
145 SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
146 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,
147 number_of_entries) {}
148
149 // Arena for permanent symbols (null class loader) that are never unloaded
150 static Arena* _arena;
151 static Arena* arena() { return _arena; } // called for statistics
152
153 static void initialize_symbols(int arena_alloc_size = 0);
154
155 static volatile int _parallel_claimed_idx;
156
157 typedef SymbolTable::BucketUnlinkContext BucketUnlinkContext;
158 // Release any dead symbols. Unlinked bucket entries are collected in the given
159 // context to be freed later.
160 // This allows multiple threads to work on the table at once.
161 static void buckets_unlink(int start_idx, int end_idx, BucketUnlinkContext* context);
162 public:
163 enum {
164 symbol_alloc_batch_size = 8,
165 // Pick initial size based on java -version size measurements
166 symbol_alloc_arena_size = 360*K
167 };
168
169 // The symbol table
170 static SymbolTable* the_table() { return _the_table; }
171 TableStatistics get_table_statistics();
172
173 // Size of one bucket in the string table. Used when checking for rollover.
174 static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
175
176 static void create_table() {
177 assert(_the_table == NULL, "One symbol table allowed.");
178 _the_table = new SymbolTable();
179 initialize_symbols(symbol_alloc_arena_size);
180 }
181
182 static unsigned int hash_symbol(const char* s, int len);
183 static unsigned int hash_shared_symbol(const char* s, int len);
184
185 static Symbol* lookup(const char* name, int len, TRAPS);
186 // lookup only, won't add. Also calculate hash.
187 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
188 // Only copy to C string to be added if lookup failed.
189 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
190
191 static void release(Symbol* sym);
192
193 // Look up the address of the literal in the SymbolTable for this Symbol*
194 static Symbol** lookup_symbol_addr(Symbol* sym);
195
196 // jchar (UTF16) version of lookups
197 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
198 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
199
200 static void add(ClassLoaderData* loader_data,
201 const constantPoolHandle& cp, int names_count,
202 const char** names, int* lengths, int* cp_indices,
203 unsigned int* hashValues, TRAPS);
204
205 // Release any dead symbols
206 static void unlink() {
207 int processed = 0;
208 int removed = 0;
209 unlink(&processed, &removed);
210 }
211 static void unlink(int* processed, int* removed);
212 // Release any dead symbols, possibly parallel version
213 static void possibly_parallel_unlink(int* processed, int* removed);
214
215 // iterate over symbols
216 static void symbols_do(SymbolClosure *cl);
217 static void metaspace_pointers_do(MetaspaceClosure* it);
218
219 // Symbol creation
220 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
221 assert(utf8_buffer != NULL, "just checking");
222 return lookup(utf8_buffer, length, THREAD);
223 }
224 static Symbol* new_symbol(const char* name, TRAPS) {
225 return new_symbol(name, (int)strlen(name), THREAD);
226 }
227 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
228 assert(begin <= end && end <= sym->utf8_length(), "just checking");
229 return lookup(sym, begin, end, THREAD);
230 }
231
232 // Create a symbol in the arena for symbols that are not deleted
233 static Symbol* new_permanent_symbol(const char* name, TRAPS);
234
235 // Symbol lookup
236 static Symbol* lookup(int index, const char* name, int len, TRAPS);
237
238 // Needed for preloading classes in signatures when compiling.
239 // Returns the symbol is already present in symbol table, otherwise
240 // NULL. NO ALLOCATION IS GUARANTEED!
241 static Symbol* probe(const char* name, int len) {
242 unsigned int ignore_hash;
243 return lookup_only(name, len, ignore_hash);
244 }
245 static Symbol* probe_unicode(const jchar* name, int len) {
246 unsigned int ignore_hash;
247 return lookup_only_unicode(name, len, ignore_hash);
248 }
249
250 // Histogram
251 static void print_histogram() PRODUCT_RETURN;
252 static void print() PRODUCT_RETURN;
253
254 // Debugging
255 static void verify();
256 static void dump(outputStream* st, bool verbose=false);
257 static void read(const char* filename, TRAPS);
258
259 // Sharing
260 static void write_to_archive();
261 static void serialize(SerializeClosure* soc);
262 static u4 encode_shared(Symbol* sym);
263 static Symbol* decode_shared(u4 offset);
264
265 // Rehash the symbol table if it gets out of balance
266 static void rehash_table();
267 static bool needs_rehashing() { return _needs_rehashing; }
268 // Parallel chunked scanning
269 static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
270 static int parallel_claimed_index() { return _parallel_claimed_idx; }
271 };
272
273 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP