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 template <class T, class N> class CompactHashtable;
88 class CompactSymbolTableWriter;
89 class SerializeClosure;
90
91 class SymbolTableConfig;
92 typedef ConcurrentHashTable<Symbol*,
93 SymbolTableConfig, mtSymbol> SymbolTableHash;
94
95 class SymbolTableCreateEntry;
96
97 class SymbolTable : public CHeapObj<mtSymbol> {
98 friend class VMStructs;
99 friend class Symbol;
100 friend class ClassFileParser;
101 friend class SymbolTableConfig;
102 friend class SymbolTableCreateEntry;
103
104 private:
105 static void delete_symbol(Symbol* sym);
106 void grow(JavaThread* jt);
107 void clean_dead_entries(JavaThread* jt);
108
109 // The symbol table
110 static SymbolTable* _the_table;
111 // Shared symbol table.
112 static CompactHashtable<Symbol*, char> _shared_table;
113 static volatile bool _lookup_shared_first;
114 static volatile bool _alt_hash;
115
116 // For statistics
117 volatile size_t _symbols_removed;
118 volatile size_t _symbols_counted;
119
120 SymbolTableHash* _local_table;
121 size_t _current_size;
122 volatile bool _has_work;
123 // Set if one bucket is out of balance due to hash algorithm deficiency
124 volatile bool _needs_rehashing;
125
126 volatile size_t _items_count;
127 volatile size_t _uncleaned_items_count;
128
129 double get_load_factor();
130 double get_dead_factor();
131
132 void check_concurrent_work();
133 void trigger_concurrent_work();
134
135 static void item_added();
136 static void item_removed();
137 static void set_item_clean_count(size_t ncl);
138 static void mark_item_clean_count();
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 add(ClassLoaderData* loader_data,
148 const constantPoolHandle& cp, int names_count,
149 const char** names, int* lengths, int* cp_indices,
150 unsigned int* hashValues, TRAPS);
151
152 static void new_symbols(ClassLoaderData* loader_data,
153 const constantPoolHandle& cp, int names_count,
154 const char** name, int* lengths,
155 int* cp_indices, unsigned int* hashValues,
156 TRAPS) {
157 add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);
158 }
159
160 static Symbol* lookup_shared(const char* name, int len, unsigned int hash);
161 Symbol* lookup_dynamic(const char* name, int len, unsigned int hash);
162 Symbol* lookup_common(const char* name, int len, unsigned int hash);
163
164 // Arena for permanent symbols (null class loader) that are never unloaded
165 static Arena* _arena;
166 static Arena* arena() { return _arena; } // called for statistics
167
168 static void initialize_symbols(int arena_alloc_size = 0);
169
170 void concurrent_work(JavaThread* jt);
171 void print_table_statistics(outputStream* st, const char* table_name);
172
173 void try_rehash_table();
174 bool do_rehash();
175
176 public:
177 // The symbol table
178 static SymbolTable* the_table() { return _the_table; }
179 size_t table_size(Thread* thread = NULL);
180
181 enum {
182 symbol_alloc_batch_size = 8,
183 // Pick initial size based on java -version size measurements
184 symbol_alloc_arena_size = 360*K // TODO (revisit)
185 };
186
187 static void create_table() {
188 assert(_the_table == NULL, "One symbol table allowed.");
189 _the_table = new SymbolTable();
190 initialize_symbols(symbol_alloc_arena_size);
191 }
192
193 static void unlink() {
194 do_check_concurrent_work();
195 }
196 static void do_check_concurrent_work();
197 static void do_concurrent_work(JavaThread* jt);
198 static bool has_work() { return the_table()->_has_work; }
199
200 // Probing
201 static Symbol* lookup(const char* name, int len, TRAPS);
202 // lookup only, won't add. Also calculate hash.
203 static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
204 // Only copy to C string to be added if lookup failed.
205 static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);
206 // jchar (UTF16) version of lookups
207 static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);
208 static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);
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 // Symbol creation
222 static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
223 assert(utf8_buffer != NULL, "just checking");
224 return lookup(utf8_buffer, length, THREAD);
225 }
226 static Symbol* new_symbol(const char* name, TRAPS) {
227 return new_symbol(name, (int)strlen(name), THREAD);
228 }
229 static Symbol* new_symbol(const Symbol* sym, int begin, int end, TRAPS) {
230 assert(begin <= end && end <= sym->utf8_length(), "just checking");
231 return lookup(sym, begin, end, THREAD);
232 }
233 // Create a symbol in the arena for symbols that are not deleted
234 static Symbol* new_permanent_symbol(const char* name, TRAPS);
235
236 // Rehash the string table if it gets out of balance
237 static void rehash_table();
238 static bool needs_rehashing()
239 { return SymbolTable::the_table()->_needs_rehashing; }
240
241 // Heap dumper and CDS
242 static void symbols_do(SymbolClosure *cl);
243
244 // Sharing
245 private:
246 static void copy_shared_symbol_table(CompactSymbolTableWriter* ch_table);
247 public:
248 static void write_to_archive() NOT_CDS_RETURN;
249 static void serialize(SerializeClosure* soc) NOT_CDS_RETURN;
250 static void metaspace_pointers_do(MetaspaceClosure* it);
251
252 // Jcmd
253 static void dump(outputStream* st, bool verbose=false);
254 // Debugging
255 static void verify();
256 static void read(const char* filename, TRAPS);
257
258 // Histogram
259 static void print_histogram() PRODUCT_RETURN;
260 };
261
262 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP