1 /*
2 * Copyright (c) 1997, 2018, 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.
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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 "memory/padded.hpp"
30 #include "oops/symbol.hpp"
31 #include "utilities/concurrentHashTable.hpp"
32 #include "utilities/hashtable.hpp"
33
34 // TempNewSymbol acts as a handle class in a handle/body idiom and is
35 // responsible for proper resource management of the body (which is a Symbol*).
36 // The body is resource managed by a reference counting scheme.
37 // TempNewSymbol can therefore be used to properly hold a newly created or referenced
38 // Symbol* temporarily in scope.
39 //
40 // Routines in SymbolTable will initialize the reference count of a Symbol* before
41 // it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol
42 // needs to maintain proper reference counting in context of copy semantics.
43 //
44 // In SymbolTable, new_symbol() and lookup() will create a Symbol* if not already in the
45 // symbol table and add to the symbol's reference count.
46 // probe() and lookup_only() will increment the refcount if symbol is found.
47 class TempNewSymbol : public StackObj {
48 Symbol* _temp;
49
50 public:
51 TempNewSymbol() : _temp(NULL) {}
52
53 // Conversion from a Symbol* to a TempNewSymbol.
54 // Does not increment the current reference count.
55 TempNewSymbol(Symbol *s) : _temp(s) {}
56
57 // Copy constructor increments reference count.
58 TempNewSymbol(const TempNewSymbol& rhs) : _temp(rhs._temp) {
59 if (_temp != NULL) {
60 _temp->increment_refcount();
61 }
62 }
63
64 // Assignment operator uses a c++ trick called copy and swap idiom.
65 // rhs is passed by value so within the scope of this method it is a copy.
66 // At method exit it contains the former value of _temp, triggering the correct refcount
67 // decrement upon destruction.
68 void operator=(TempNewSymbol rhs) {
69 Symbol* tmp = rhs._temp;
70 rhs._temp = _temp;
71 _temp = tmp;
72 }
73
74 // Decrement reference counter so it can go away if it's unused
75 ~TempNewSymbol() {
76 if (_temp != NULL) {
77 _temp->decrement_refcount();
78 }
79 }
80
81 // Symbol* conversion operators
82 Symbol* operator -> () const { return _temp; }
83 bool operator == (Symbol* o) const { return _temp == o; }
84 operator Symbol*() { return _temp; }
85 };
86
87 class CompactSymbolTableWriter;
88 class SerializeClosure;
89
90 class SymbolTableConfig;
91 typedef ConcurrentHashTable<Symbol*,
92 SymbolTableConfig, mtSymbol> SymbolTableHash;
93
94 class SymbolTableCreateEntry;
95
96 class SymbolTable : public CHeapObj<mtSymbol> {
97 friend class VMStructs;
98 friend class Symbol;
99 friend class ClassFileParser;
100 friend class SymbolTableConfig;
101 friend class SymbolTableCreateEntry;
102
103 private:
104 static void delete_symbol(Symbol* sym);
105 void grow(JavaThread* jt);
106 void clean_dead_entries(JavaThread* jt);
107
108 // The symbol table
109 static SymbolTable* _the_table;
110 static volatile bool _lookup_shared_first;
111 static volatile bool _alt_hash;
112
113 // For statistics
114 volatile size_t _symbols_removed;
115 volatile size_t _symbols_counted;
116
117 SymbolTableHash* _local_table;
118 size_t _current_size;
119 volatile bool _has_work;
120 // Set if one bucket is out of balance due to hash algorithm deficiency
121 volatile bool _needs_rehashing;
122
123 volatile size_t _items_count;
124 volatile size_t _uncleaned_items_count;
125
126 double get_load_factor();
127 double get_dead_factor();
128
129 void check_concurrent_work();
130 void trigger_concurrent_work();
131
132 static void item_added();
133 static void item_removed();
134 static void set_item_clean_count(size_t ncl);
135 static void mark_item_clean_count();
136
137 SymbolTable();
138
139 Symbol* allocate_symbol(const char* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F
140 Symbol* do_lookup(const char* name, int len, uintx hash);
141 Symbol* do_add_if_needed(const char* name, int len, uintx hash, bool heap, TRAPS);
142
143 // Adding elements
144 static void add(ClassLoaderData* loader_data,
145 const constantPoolHandle& cp, int names_count,
146 const char** names, int* lengths, int* cp_indices,
147 unsigned int* hashValues, TRAPS);
148
149 static void new_symbols(ClassLoaderData* loader_data,
150 const constantPoolHandle& cp, int names_count,
151 const char** name, int* lengths,
152 int* cp_indices, unsigned int* hashValues,
153 TRAPS) {
154 add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);
155 }
156
157 static Symbol* lookup_shared(const char* name, int len, unsigned int hash);
158 Symbol* lookup_dynamic(const char* name, int len, unsigned int hash);
159 Symbol* lookup_common(const char* name, int len, unsigned int hash);
160
161 // Arena for permanent symbols (null class loader) that are never unloaded
162 static Arena* _arena;
163 static Arena* arena() { return _arena; } // called for statistics
164
165 static void initialize_symbols(int arena_alloc_size = 0);
166
167 void concurrent_work(JavaThread* jt);
168 void print_table_statistics(outputStream* st, const char* table_name);
169
170 void try_rehash_table();
171 bool do_rehash();
172
173 public:
174 // The symbol table
175 static SymbolTable* the_table() { return _the_table; }
176 size_t table_size();
177
178 enum {
179 symbol_alloc_batch_size = 8,
180 // Pick initial size based on java -version size measurements
181 symbol_alloc_arena_size = 360*K // TODO (revisit)
182 };
183
184 static void create_table() {
185 assert(_the_table == NULL, "One symbol table allowed.");
186 _the_table = new SymbolTable();
187 initialize_symbols(symbol_alloc_arena_size);
188 }
189
190 static void unlink() {
191 do_check_concurrent_work();
192 }
193 static void do_check_concurrent_work();
194 static void do_concurrent_work(JavaThread* jt);
195 static bool has_work() { return the_table()->_has_work; }
196
197 // Probing
198 static Symbol* lookup(const char* name, int len, TRAPS);
199 // lookup only, won't add. Also calculate hash.
200 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
201 // adds new symbol if not found
202 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
203 // jchar (UTF16) version of lookups
204 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
205 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
206 // Needed for preloading classes in signatures when compiling.
207 // Returns the symbol is already present in symbol table, otherwise
208 // NULL. NO ALLOCATION IS GUARANTEED!
209 static Symbol* probe(const char* name, int len) {
210 unsigned int ignore_hash;
211 return lookup_only(name, len, ignore_hash);
212 }
213 static Symbol* probe_unicode(const jchar* name, int len) {
214 unsigned int ignore_hash;
215 return lookup_only_unicode(name, len, ignore_hash);
216 }
217
218 // Symbol creation
219 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
220 assert(utf8_buffer != NULL, "just checking");
221 return lookup(utf8_buffer, length, THREAD);
222 }
223 static Symbol* new_symbol(const char* name, TRAPS) {
224 return new_symbol(name, (int)strlen(name), THREAD);
225 }
226 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
227 assert(begin <= end && end <= sym->utf8_length(), "just checking");
228 return lookup(sym, begin, end, THREAD);
229 }
230 // Create a symbol in the arena for symbols that are not deleted
231 static Symbol* new_permanent_symbol(const char* name, TRAPS);
232
233 // Rehash the string table if it gets out of balance
234 static void rehash_table();
235 static bool needs_rehashing()
236 { return SymbolTable::the_table()->_needs_rehashing; }
237
238 // Heap dumper and CDS
239 static void symbols_do(SymbolClosure *cl);
240
241 // Sharing
242 private:
243 static void copy_shared_symbol_table(CompactSymbolTableWriter* ch_table);
244 public:
245 static void write_to_archive() NOT_CDS_RETURN;
246 static void serialize(SerializeClosure* soc) NOT_CDS_RETURN;
247 static void metaspace_pointers_do(MetaspaceClosure* it);
248
249 // Jcmd
250 static void dump(outputStream* st, bool verbose=false);
251 // Debugging
252 static void verify();
253 static void read(const char* filename, TRAPS);
254
255 // Histogram
256 static void print_histogram() PRODUCT_RETURN;
257 };
258
259 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP