1 /*
2 * Copyright (c) 1997, 2015, 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 #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 // Class to hold a newly created or referenced Symbol* temporarily in scope.
46 // new_symbol() and lookup() will create a Symbol* if not already in the
47 // symbol table and add to the symbol's reference count.
48 // probe() and lookup_only() will increment the refcount if symbol is found.
49 class TempNewSymbol : public StackObj {
50 Symbol* _temp;
51
52 public:
53 TempNewSymbol() : _temp(NULL) {}
54 // Creating or looking up a symbol increments the symbol's reference count
55 TempNewSymbol(Symbol *s) : _temp(s) {}
56
57 // Operator= increments reference count.
58 void operator=(const TempNewSymbol &s) {
59 //clear(); //FIXME
60 _temp = s._temp;
61 if (_temp !=NULL) _temp->increment_refcount();
62 }
63
64 // Decrement reference counter so it can go away if it's unique
65 void clear() { if (_temp != NULL) _temp->decrement_refcount(); _temp = NULL; }
66
67 ~TempNewSymbol() { clear(); }
68
69 // Operators so they can be used like Symbols
70 Symbol* operator -> () const { return _temp; }
71 bool operator == (Symbol* o) const { return _temp == o; }
72 // Sneaky conversion function
73 operator Symbol*() { return _temp; }
74 };
75
76 template <class T, class N> class CompactHashtable;
77
78 class SymbolTable : public RehashableHashtable<Symbol*, mtSymbol> {
79 friend class VMStructs;
80 friend class ClassFileParser;
81
82 private:
83 // The symbol table
84 static SymbolTable* _the_table;
85
86 // Set if one bucket is out of balance due to hash algorithm deficiency
87 static bool _needs_rehashing;
88 static bool _lookup_shared_first;
89
90 // For statistics
91 static int _symbols_removed;
92 static int _symbols_counted;
93
94 // shared symbol table.
95 static CompactHashtable<Symbol*, char> _shared_table;
96
97 Symbol* allocate_symbol(const u1* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F
98
99 // Adding elements
100 Symbol* basic_add(int index, u1* name, int len, unsigned int hashValue,
101 bool c_heap, TRAPS);
102 bool basic_add(ClassLoaderData* loader_data,
103 const constantPoolHandle& cp, int names_count,
104 const char** names, int* lengths, int* cp_indices,
105 unsigned int* hashValues, TRAPS);
106
107 static void new_symbols(ClassLoaderData* loader_data,
108 const constantPoolHandle& cp, int names_count,
109 const char** name, int* lengths,
110 int* cp_indices, unsigned int* hashValues,
111 TRAPS) {
112 add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);
113 }
114
115 static Symbol* lookup_shared(const char* name, int len, unsigned int hash);
116 Symbol* lookup_dynamic(int index, const char* name, int len, unsigned int hash);
117 Symbol* lookup(int index, const char* name, int len, unsigned int hash);
118
119 SymbolTable()
120 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}
121
122 SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
123 : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,
124 number_of_entries) {}
125
126 // Arena for permanent symbols (null class loader) that are never unloaded
127 static Arena* _arena;
128 static Arena* arena() { return _arena; } // called for statistics
129
130 static void initialize_symbols(int arena_alloc_size = 0);
131
132 static volatile int _parallel_claimed_idx;
133
134 // Release any dead symbols
135 static void buckets_unlink(int start_idx, int end_idx, int* processed, int* removed);
136 public:
137 enum {
138 symbol_alloc_batch_size = 8,
139 // Pick initial size based on java -version size measurements
140 symbol_alloc_arena_size = 360*K
141 };
142
143 // The symbol table
144 static SymbolTable* the_table() { return _the_table; }
145
146 // Size of one bucket in the string table. Used when checking for rollover.
147 static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
148
149 static void create_table() {
150 assert(_the_table == NULL, "One symbol table allowed.");
151 _the_table = new SymbolTable();
152 initialize_symbols(symbol_alloc_arena_size);
153 }
154
155 static unsigned int hash_symbol(const char* s, int len);
156
157 static Symbol* lookup(const char* name, int len, TRAPS);
158 // lookup only, won't add. Also calculate hash.
159 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
160 // Only copy to C string to be added if lookup failed.
161 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
162
163 static void release(Symbol* sym);
164
165 // Look up the address of the literal in the SymbolTable for this Symbol*
166 static Symbol** lookup_symbol_addr(Symbol* sym);
167
168 // jchar (UTF16) version of lookups
169 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
170 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
171
172 static void add(ClassLoaderData* loader_data,
173 const constantPoolHandle& cp, int names_count,
174 const char** names, int* lengths, int* cp_indices,
175 unsigned int* hashValues, TRAPS);
176
177 // Release any dead symbols
178 static void unlink() {
179 int processed = 0;
180 int removed = 0;
181 unlink(&processed, &removed);
182 }
183 static void unlink(int* processed, int* removed);
184 // Release any dead symbols, possibly parallel version
185 static void possibly_parallel_unlink(int* processed, int* removed);
186
187 // iterate over symbols
188 static void symbols_do(SymbolClosure *cl);
189
190 // Symbol creation
191 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
192 assert(utf8_buffer != NULL, "just checking");
193 return lookup(utf8_buffer, length, THREAD);
194 }
195 static Symbol* new_symbol(const char* name, TRAPS) {
196 return new_symbol(name, (int)strlen(name), THREAD);
197 }
198 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
199 assert(begin <= end && end <= sym->utf8_length(), "just checking");
200 return lookup(sym, begin, end, THREAD);
201 }
202
203 // Create a symbol in the arena for symbols that are not deleted
204 static Symbol* new_permanent_symbol(const char* name, TRAPS);
205
206 // Symbol lookup
207 static Symbol* lookup(int index, const char* name, int len, TRAPS);
208
209 // Needed for preloading classes in signatures when compiling.
210 // Returns the symbol is already present in symbol table, otherwise
211 // NULL. NO ALLOCATION IS GUARANTEED!
212 static Symbol* probe(const char* name, int len) {
213 unsigned int ignore_hash;
214 return lookup_only(name, len, ignore_hash);
215 }
216 static Symbol* probe_unicode(const jchar* name, int len) {
217 unsigned int ignore_hash;
218 return lookup_only_unicode(name, len, ignore_hash);
219 }
220
221 // Histogram
222 static void print_histogram() PRODUCT_RETURN;
223 static void print() PRODUCT_RETURN;
224
225 // Debugging
226 static void verify();
227 static void dump(outputStream* st, bool verbose=false);
228 static void read(const char* filename, TRAPS);
229
230 // Sharing
231 static bool copy_compact_table(char** top, char* end);
232 static const char* init_shared_table(const char* buffer);
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 // Parallel chunked scanning
238 static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
239 static int parallel_claimed_index() { return _parallel_claimed_idx; }
240 };
241
242 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP