hashtable.hpp revision 3440:246d977b51f2
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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_UTILITIES_HASHTABLE_HPP 26#define SHARE_VM_UTILITIES_HASHTABLE_HPP 27 28#include "memory/allocation.hpp" 29#include "oops/oop.hpp" 30#include "oops/symbol.hpp" 31#include "runtime/handles.hpp" 32 33// This is a generic hashtable, designed to be used for the symbol 34// and string tables. 35// 36// It is implemented as an open hash table with a fixed number of buckets. 37// 38// %note: 39// - TableEntrys are allocated in blocks to reduce the space overhead. 40 41 42 43class BasicHashtableEntry : public CHeapObj { 44 friend class VMStructs; 45private: 46 unsigned int _hash; // 32-bit hash for item 47 48 // Link to next element in the linked list for this bucket. EXCEPT 49 // bit 0 set indicates that this entry is shared and must not be 50 // unlinked from the table. Bit 0 is set during the dumping of the 51 // archive. Since shared entries are immutable, _next fields in the 52 // shared entries will not change. New entries will always be 53 // unshared and since pointers are align, bit 0 will always remain 0 54 // with no extra effort. 55 BasicHashtableEntry* _next; 56 57 // Windows IA64 compiler requires subclasses to be able to access these 58protected: 59 // Entry objects should not be created, they should be taken from the 60 // free list with BasicHashtable.new_entry(). 61 BasicHashtableEntry() { ShouldNotReachHere(); } 62 // Entry objects should not be destroyed. They should be placed on 63 // the free list instead with BasicHashtable.free_entry(). 64 ~BasicHashtableEntry() { ShouldNotReachHere(); } 65 66public: 67 68 unsigned int hash() const { return _hash; } 69 void set_hash(unsigned int hash) { _hash = hash; } 70 unsigned int* hash_addr() { return &_hash; } 71 72 static BasicHashtableEntry* make_ptr(BasicHashtableEntry* p) { 73 return (BasicHashtableEntry*)((intptr_t)p & -2); 74 } 75 76 BasicHashtableEntry* next() const { 77 return make_ptr(_next); 78 } 79 80 void set_next(BasicHashtableEntry* next) { 81 _next = next; 82 } 83 84 BasicHashtableEntry** next_addr() { 85 return &_next; 86 } 87 88 bool is_shared() const { 89 return ((intptr_t)_next & 1) != 0; 90 } 91 92 void set_shared() { 93 _next = (BasicHashtableEntry*)((intptr_t)_next | 1); 94 } 95}; 96 97 98 99template <class T> class HashtableEntry : public BasicHashtableEntry { 100 friend class VMStructs; 101private: 102 T _literal; // ref to item in table. 103 104public: 105 // Literal 106 T literal() const { return _literal; } 107 T* literal_addr() { return &_literal; } 108 void set_literal(T s) { _literal = s; } 109 110 HashtableEntry* next() const { 111 return (HashtableEntry*)BasicHashtableEntry::next(); 112 } 113 HashtableEntry** next_addr() { 114 return (HashtableEntry**)BasicHashtableEntry::next_addr(); 115 } 116}; 117 118 119 120class HashtableBucket : public CHeapObj { 121 friend class VMStructs; 122private: 123 // Instance variable 124 BasicHashtableEntry* _entry; 125 126public: 127 // Accessing 128 void clear() { _entry = NULL; } 129 130 // The following methods use order access methods to avoid race 131 // conditions in multiprocessor systems. 132 BasicHashtableEntry* get_entry() const; 133 void set_entry(BasicHashtableEntry* l); 134 135 // The following method is not MT-safe and must be done under lock. 136 BasicHashtableEntry** entry_addr() { return &_entry; } 137}; 138 139 140class BasicHashtable : public CHeapObj { 141 friend class VMStructs; 142 143public: 144 BasicHashtable(int table_size, int entry_size); 145 BasicHashtable(int table_size, int entry_size, 146 HashtableBucket* buckets, int number_of_entries); 147 148 // Sharing support. 149 void copy_buckets(char** top, char* end); 150 void copy_table(char** top, char* end); 151 152 // Bucket handling 153 int hash_to_index(unsigned int full_hash) { 154 int h = full_hash % _table_size; 155 assert(h >= 0 && h < _table_size, "Illegal hash value"); 156 return h; 157 } 158 159 // Reverse the order of elements in each of the buckets. 160 void reverse(); 161 162private: 163 // Instance variables 164 int _table_size; 165 HashtableBucket* _buckets; 166 BasicHashtableEntry* _free_list; 167 char* _first_free_entry; 168 char* _end_block; 169 int _entry_size; 170 int _number_of_entries; 171 172protected: 173 174#ifdef ASSERT 175 int _lookup_count; 176 int _lookup_length; 177 void verify_lookup_length(double load); 178#endif 179 180 enum { 181 rehash_count = 100, 182 rehash_multiple = 60 183 }; 184 185 void initialize(int table_size, int entry_size, int number_of_entries); 186 187 // Accessor 188 int entry_size() const { return _entry_size; } 189 190 // The following method is MT-safe and may be used with caution. 191 BasicHashtableEntry* bucket(int i); 192 193 // The following method is not MT-safe and must be done under lock. 194 BasicHashtableEntry** bucket_addr(int i) { return _buckets[i].entry_addr(); } 195 196 // Table entry management 197 BasicHashtableEntry* new_entry(unsigned int hashValue); 198 199 // Check that the table is unbalanced 200 bool check_rehash_table(int count); 201 202 // Used when moving the entry to another table 203 // Clean up links, but do not add to free_list 204 void unlink_entry(BasicHashtableEntry* entry) { 205 entry->set_next(NULL); 206 --_number_of_entries; 207 } 208 209 // Move over freelist and free block for allocation 210 void copy_freelist(BasicHashtable* src) { 211 _free_list = src->_free_list; 212 src->_free_list = NULL; 213 _first_free_entry = src->_first_free_entry; 214 src->_first_free_entry = NULL; 215 _end_block = src->_end_block; 216 src->_end_block = NULL; 217 } 218 219 // Free the buckets in this hashtable 220 void free_buckets(); 221 222public: 223 int table_size() { return _table_size; } 224 void set_entry(int index, BasicHashtableEntry* entry); 225 226 void add_entry(int index, BasicHashtableEntry* entry); 227 228 void free_entry(BasicHashtableEntry* entry); 229 230 int number_of_entries() { return _number_of_entries; } 231 232 void verify() PRODUCT_RETURN; 233}; 234 235 236template <class T> class Hashtable : public BasicHashtable { 237 friend class VMStructs; 238 239public: 240 Hashtable(int table_size, int entry_size) 241 : BasicHashtable(table_size, entry_size) { } 242 243 Hashtable(int table_size, int entry_size, 244 HashtableBucket* buckets, int number_of_entries) 245 : BasicHashtable(table_size, entry_size, buckets, number_of_entries) { } 246 247 // Debugging 248 void print() PRODUCT_RETURN; 249 250 // Reverse the order of elements in each of the buckets. Hashtable 251 // entries which refer to objects at a lower address than 'boundary' 252 // are separated from those which refer to objects at higher 253 // addresses, and appear first in the list. 254 void reverse(void* boundary = NULL); 255 256protected: 257 258 unsigned int compute_hash(Symbol* name) { 259 return (unsigned int) name->identity_hash(); 260 } 261 262 int index_for(Symbol* name) { 263 return hash_to_index(compute_hash(name)); 264 } 265 266 // Table entry management 267 HashtableEntry<T>* new_entry(unsigned int hashValue, T obj); 268 269 // The following method is MT-safe and may be used with caution. 270 HashtableEntry<T>* bucket(int i) { 271 return (HashtableEntry<T>*)BasicHashtable::bucket(i); 272 } 273 274 // The following method is not MT-safe and must be done under lock. 275 HashtableEntry<T>** bucket_addr(int i) { 276 return (HashtableEntry<T>**)BasicHashtable::bucket_addr(i); 277 } 278 279 // Function to move these elements into the new table. 280 void move_to(Hashtable<T>* new_table); 281 virtual unsigned int new_hash(T) { ShouldNotReachHere(); return 0; } // should be overridden 282}; 283 284 285// Verions of hashtable where two handles are used to compute the index. 286 287template <class T> class TwoOopHashtable : public Hashtable<T> { 288 friend class VMStructs; 289protected: 290 TwoOopHashtable(int table_size, int entry_size) 291 : Hashtable<T>(table_size, entry_size) {} 292 293 TwoOopHashtable(int table_size, int entry_size, HashtableBucket* t, 294 int number_of_entries) 295 : Hashtable<T>(table_size, entry_size, t, number_of_entries) {} 296 297public: 298 unsigned int compute_hash(Symbol* name, Handle loader) { 299 // Be careful with identity_hash(), it can safepoint and if this 300 // were one expression, the compiler could choose to unhandle each 301 // oop before calling identity_hash() for either of them. If the first 302 // causes a GC, the next would fail. 303 unsigned int name_hash = name->identity_hash(); 304 unsigned int loader_hash = loader.is_null() ? 0 : loader->identity_hash(); 305 return name_hash ^ loader_hash; 306 } 307 308 int index_for(Symbol* name, Handle loader) { 309 return this->hash_to_index(compute_hash(name, loader)); 310 } 311}; 312 313#endif // SHARE_VM_UTILITIES_HASHTABLE_HPP 314