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_OOPS_SYMBOL_HPP
26 #define SHARE_VM_OOPS_SYMBOL_HPP
27
28 #include "utilities/utf8.hpp"
29 #include "memory/allocation.hpp"
30
31 // A Symbol is a canonicalized string.
32 // All Symbols reside in global SymbolTable and are reference counted.
33
34 // Reference counting
35 //
36 // All Symbols are allocated and added to the SymbolTable.
37 // When a class is unloaded, the reference counts of the Symbol pointers in
38 // the ConstantPool and in InstanceKlass (see release_C_heap_structures) are
39 // decremented. When the reference count for a Symbol goes to 0, the garbage
40 // collector can free the Symbol and remove it from the SymbolTable.
41 //
42 // 0) Symbols need to be reference counted when a pointer to the Symbol is
43 // saved in persistent storage. This does not include the pointer
44 // in the SymbolTable bucket (the _literal field in HashtableEntry)
45 // that points to the Symbol. All other stores of a Symbol*
46 // to a field of a persistent variable (e.g., the _name filed in
47 // FieldAccessInfo or _ptr in a CPSlot) is reference counted.
48 //
49 // 1) The lookup of a "name" in the SymbolTable either creates a Symbol F for
84 //
85 // 3) When a Symbol K is created for temporary use, generally for substrings of
86 // an existing symbol or to create a new symbol, assign it to a
87 // TempNewSymbol. The SymbolTable methods new_symbol(), lookup()
88 // and probe() all potentially return a pointer to a new Symbol.
89 // The allocation (or lookup) of K increments the reference count for K
90 // and the destructor decrements the reference count.
91 //
92 // Another example of TempNewSymbol usage is parsed_name used in
93 // ClassFileParser::parseClassFile() where parsed_name is used in the cleanup
94 // after a failed attempt to load a class. Here parsed_name is a
95 // TempNewSymbol (passed in as a parameter) so the reference count on its symbol
96 // will be decremented when it goes out of scope.
97
98
99 // This cannot be inherited from ResourceObj because it cannot have a vtable.
100 // Since sometimes this is allocated from Metadata, pick a base allocation
101 // type without virtual functions.
102 class ClassLoaderData;
103
104 class Symbol : public MetaspaceObj {
105 friend class VMStructs;
106 friend class SymbolTable;
107 friend class MoveSymbols;
108 private:
109 volatile int _refcount;
110 int _identity_hash;
111 unsigned short _length; // number of UTF8 characters in the symbol
112 jbyte _body[1];
113
114 enum {
115 // max_symbol_length is constrained by type of _length
116 max_symbol_length = (1 << 16) -1
117 };
118
119 static int size(int length) {
120 size_t sz = heap_word_size(sizeof(Symbol) + (length > 0 ? length - 1 : 0));
121 return align_object_size(sz);
122 }
123
124 void byte_at_put(int index, int value) {
125 assert(index >=0 && index < _length, "symbol index overflow");
126 _body[index] = value;
127 }
128
129 Symbol(const u1* name, int length, int refcount);
130 void* operator new(size_t size, int len, TRAPS);
131 void* operator new(size_t size, int len, Arena* arena, TRAPS);
132 void* operator new(size_t size, int len, ClassLoaderData* loader_data, TRAPS);
133
134 void operator delete(void* p);
135
136 public:
137 // Low-level access (used with care, since not GC-safe)
138 const jbyte* base() const { return &_body[0]; }
139
140 int size() { return size(utf8_length()); }
|
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_OOPS_SYMBOL_HPP
26 #define SHARE_VM_OOPS_SYMBOL_HPP
27
28 #include "utilities/utf8.hpp"
29 #include "memory/allocation.hpp"
30 #include "runtime/atomic.hpp"
31
32 // A Symbol is a canonicalized string.
33 // All Symbols reside in global SymbolTable and are reference counted.
34
35 // Reference counting
36 //
37 // All Symbols are allocated and added to the SymbolTable.
38 // When a class is unloaded, the reference counts of the Symbol pointers in
39 // the ConstantPool and in InstanceKlass (see release_C_heap_structures) are
40 // decremented. When the reference count for a Symbol goes to 0, the garbage
41 // collector can free the Symbol and remove it from the SymbolTable.
42 //
43 // 0) Symbols need to be reference counted when a pointer to the Symbol is
44 // saved in persistent storage. This does not include the pointer
45 // in the SymbolTable bucket (the _literal field in HashtableEntry)
46 // that points to the Symbol. All other stores of a Symbol*
47 // to a field of a persistent variable (e.g., the _name filed in
48 // FieldAccessInfo or _ptr in a CPSlot) is reference counted.
49 //
50 // 1) The lookup of a "name" in the SymbolTable either creates a Symbol F for
85 //
86 // 3) When a Symbol K is created for temporary use, generally for substrings of
87 // an existing symbol or to create a new symbol, assign it to a
88 // TempNewSymbol. The SymbolTable methods new_symbol(), lookup()
89 // and probe() all potentially return a pointer to a new Symbol.
90 // The allocation (or lookup) of K increments the reference count for K
91 // and the destructor decrements the reference count.
92 //
93 // Another example of TempNewSymbol usage is parsed_name used in
94 // ClassFileParser::parseClassFile() where parsed_name is used in the cleanup
95 // after a failed attempt to load a class. Here parsed_name is a
96 // TempNewSymbol (passed in as a parameter) so the reference count on its symbol
97 // will be decremented when it goes out of scope.
98
99
100 // This cannot be inherited from ResourceObj because it cannot have a vtable.
101 // Since sometimes this is allocated from Metadata, pick a base allocation
102 // type without virtual functions.
103 class ClassLoaderData;
104
105 // We separate the fields in SymbolBase from Symbol::_body so that
106 // Symbol::size(int) can correctly calculate the space needed.
107 class SymbolBase : public MetaspaceObj {
108 friend class VMStructs;
109 friend class SymbolTable;
110 friend class MoveSymbols;
111 public:
112 ATOMIC_SHORT_PAIR(
113 volatile short _refcount, // needs atomic operation
114 unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op)
115 );
116 int _identity_hash;
117 };
118
119 class Symbol : private SymbolBase {
120 friend class VMStructs;
121 friend class SymbolTable;
122 friend class MoveSymbols;
123 private:
124 jbyte _body[1];
125
126 enum {
127 // max_symbol_length is constrained by type of _length
128 max_symbol_length = (1 << 16) -1
129 };
130
131 static int size(int length) {
132 size_t sz = heap_word_size(sizeof(SymbolBase) + (length > 0 ? length : 0));
133 return align_object_size(sz);
134 }
135
136 void byte_at_put(int index, int value) {
137 assert(index >=0 && index < _length, "symbol index overflow");
138 _body[index] = value;
139 }
140
141 Symbol(const u1* name, int length, int refcount);
142 void* operator new(size_t size, int len, TRAPS);
143 void* operator new(size_t size, int len, Arena* arena, TRAPS);
144 void* operator new(size_t size, int len, ClassLoaderData* loader_data, TRAPS);
145
146 void operator delete(void* p);
147
148 public:
149 // Low-level access (used with care, since not GC-safe)
150 const jbyte* base() const { return &_body[0]; }
151
152 int size() { return size(utf8_length()); }
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