1 /*
2 * Copyright (c) 1997, 2019, 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_CLASSFILE_SYMBOLTABLE_HPP
26 #define SHARE_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 class JavaThread;
35
36 // TempNewSymbol acts as a handle class in a handle/body idiom and is
37 // responsible for proper resource management of the body (which is a Symbol*).
38 // The body is resource managed by a reference counting scheme.
39 // TempNewSymbol can therefore be used to properly hold a newly created or referenced
40 // Symbol* temporarily in scope.
41 //
42 // Routines in SymbolTable will initialize the reference count of a Symbol* before
43 // it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol
44 // needs to maintain proper reference counting in context of copy semantics.
45 //
46 // In SymbolTable, 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
55 // Conversion from a Symbol* to a TempNewSymbol.
56 // Does not increment the current reference count.
57 TempNewSymbol(Symbol *s) : _temp(s) {}
58
59 // Copy constructor increments reference count.
60 TempNewSymbol(const TempNewSymbol& rhs) : _temp(rhs._temp) {
61 if (_temp != NULL) {
62 _temp->increment_refcount();
63 }
64 }
65
66 // Assignment operator uses a c++ trick called copy and swap idiom.
67 // rhs is passed by value so within the scope of this method it is a copy.
68 // At method exit it contains the former value of _temp, triggering the correct refcount
69 // decrement upon destruction.
70 void operator=(TempNewSymbol rhs) {
71 Symbol* tmp = rhs._temp;
72 rhs._temp = _temp;
73 _temp = tmp;
74 }
75
76 // Decrement reference counter so it can go away if it's unused
77 ~TempNewSymbol() {
78 if (_temp != NULL) {
79 _temp->decrement_refcount();
80 }
81 }
82
83 // Symbol* conversion operators
84 Symbol* operator -> () const { return _temp; }
85 bool operator == (Symbol* o) const { return _temp == o; }
86 operator Symbol*() { return _temp; }
87 };
88
89 class CompactHashtableWriter;
90 class SerializeClosure;
91
92 class SymbolTableConfig;
93 typedef ConcurrentHashTable<Symbol*,
94 SymbolTableConfig, mtSymbol> SymbolTableHash;
95
96 class SymbolTableCreateEntry;
97
98 class SymbolTable : public CHeapObj<mtSymbol> {
99 friend class VMStructs;
100 friend class Symbol;
101 friend class ClassFileParser;
102 friend class SymbolTableConfig;
103 friend class SymbolTableCreateEntry;
104
105 private:
106 static void delete_symbol(Symbol* sym);
107 void grow(JavaThread* jt);
108 void clean_dead_entries(JavaThread* jt);
109
110 // The symbol table
111 static SymbolTable* _the_table;
112 static volatile bool _lookup_shared_first;
113 static volatile bool _alt_hash;
114
115 // For statistics
116 volatile size_t _symbols_removed;
117 volatile size_t _symbols_counted;
118
119 SymbolTableHash* _local_table;
120 size_t _current_size;
121 volatile bool _has_work;
122 // Set if one bucket is out of balance due to hash algorithm deficiency
123 volatile bool _needs_rehashing;
124
125 volatile size_t _items_count;
126 volatile bool _has_items_to_clean;
127
128 double get_load_factor() const;
129
130 void check_concurrent_work();
131
132 static void item_added();
133 static void item_removed();
134
135 // For cleaning
136 void reset_has_items_to_clean();
137 void mark_has_items_to_clean();
138 bool has_items_to_clean() const;
139
140 SymbolTable();
141
142 Symbol* allocate_symbol(const char* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F
143 Symbol* do_lookup(const char* name, int len, uintx hash);
144 Symbol* do_add_if_needed(const char* name, int len, uintx hash, bool heap, TRAPS);
145
146 // Adding elements
147 static void new_symbols(ClassLoaderData* loader_data,
148 const constantPoolHandle& cp, int names_count,
149 const char** name, int* lengths,
150 int* cp_indices, unsigned int* hashValues,
151 TRAPS);
152
153 static Symbol* lookup_shared(const char* name, int len, unsigned int hash);
154 Symbol* lookup_dynamic(const char* name, int len, unsigned int hash);
155 Symbol* lookup_common(const char* name, int len, unsigned int hash);
156
157 // Arena for permanent symbols (null class loader) that are never unloaded
158 static Arena* _arena;
159 static Arena* arena() { return _arena; } // called for statistics
160
161 static void initialize_symbols(int arena_alloc_size = 0);
162
163 void concurrent_work(JavaThread* jt);
164 void print_table_statistics(outputStream* st, const char* table_name);
165
166 void try_rehash_table();
167 bool do_rehash();
168 inline void update_needs_rehash(bool rehash);
169
170 public:
171 // The symbol table
172 static SymbolTable* the_table() { return _the_table; }
173 size_t table_size();
174
175 enum {
176 symbol_alloc_batch_size = 8,
177 // Pick initial size based on java -version size measurements
178 symbol_alloc_arena_size = 360*K // TODO (revisit)
179 };
180
181 static void create_table() {
182 assert(_the_table == NULL, "One symbol table allowed.");
183 _the_table = new SymbolTable();
184 initialize_symbols(symbol_alloc_arena_size);
185 }
186
187 static void do_concurrent_work(JavaThread* jt);
188 static bool has_work() { return the_table()->_has_work; }
189 static void trigger_cleanup();
190
191 // Probing
192 static Symbol* lookup(const char* name, int len, TRAPS);
193 // lookup only, won't add. Also calculate hash.
194 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
195 // adds new symbol if not found
196 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
197 // jchar (UTF16) version of lookups
198 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
199 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
200 // Needed for preloading classes in signatures when compiling.
201 // Returns the symbol is already present in symbol table, otherwise
202 // NULL. NO ALLOCATION IS GUARANTEED!
203 static Symbol* probe(const char* name, int len) {
204 unsigned int ignore_hash;
205 return lookup_only(name, len, ignore_hash);
206 }
207 static Symbol* probe_unicode(const jchar* name, int len) {
208 unsigned int ignore_hash;
209 return lookup_only_unicode(name, len, ignore_hash);
210 }
211
212 // Symbol creation
213 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
214 assert(utf8_buffer != NULL, "just checking");
215 return lookup(utf8_buffer, length, THREAD);
216 }
217 static Symbol* new_symbol(const char* name, TRAPS) {
218 return new_symbol(name, (int)strlen(name), THREAD);
219 }
220 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
221 assert(begin <= end && end <= sym->utf8_length(), "just checking");
222 return lookup(sym, begin, end, THREAD);
223 }
224 // Create a symbol in the arena for symbols that are not deleted
225 static Symbol* new_permanent_symbol(const char* name, TRAPS);
226
227 // Rehash the string table if it gets out of balance
228 static void rehash_table();
229 static bool needs_rehashing()
230 { return SymbolTable::the_table()->_needs_rehashing; }
231
232 // Heap dumper and CDS
233 static void symbols_do(SymbolClosure *cl);
234
235 // Sharing
236 private:
237 static void copy_shared_symbol_table(CompactHashtableWriter* ch_table);
238 public:
239 static void write_to_archive() NOT_CDS_RETURN;
240 static void serialize_shared_table_header(SerializeClosure* soc) NOT_CDS_RETURN;
241 static void metaspace_pointers_do(MetaspaceClosure* it);
242
243 // Jcmd
244 static void dump(outputStream* st, bool verbose=false);
245 // Debugging
246 static void verify();
247 static void read(const char* filename, TRAPS);
248
249 // Histogram
250 static void print_histogram() PRODUCT_RETURN;
251 };
252
253 #endif // SHARE_CLASSFILE_SYMBOLTABLE_HPP