1 /* 2 * Copyright (c) 2003, 2014, 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. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/altHashing.hpp" 27 #include "classfile/javaClasses.hpp" 28 #include "memory/allocation.inline.hpp" 29 #include "memory/filemap.hpp" 30 #include "memory/resourceArea.hpp" 31 #include "oops/oop.inline.hpp" 32 #include "runtime/safepoint.hpp" 33 #include "utilities/dtrace.hpp" 34 #include "utilities/hashtable.hpp" 35 #include "utilities/hashtable.inline.hpp" 36 #include "utilities/numberSeq.hpp" 37 38 39 // This hashtable is implemented as an open hash table with a fixed number of buckets. 40 41 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry_free_list() { 42 BasicHashtableEntry<F>* entry = NULL; 43 if (_free_list != NULL) { 44 entry = _free_list; 45 _free_list = _free_list->next(); 46 } 47 return entry; 48 } 49 50 // HashtableEntrys are allocated in blocks to reduce the space overhead. 51 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry(unsigned int hashValue) { 52 BasicHashtableEntry<F>* entry = new_entry_free_list(); 53 54 if (entry == NULL) { 55 if (_first_free_entry + _entry_size >= _end_block) { 56 int block_size = MIN2(512, MAX2((int)_table_size / 2, (int)_number_of_entries)); 57 int len = _entry_size * block_size; 58 len = 1 << log2_intptr(len); // round down to power of 2 59 assert(len >= _entry_size, ""); 60 _first_free_entry = NEW_C_HEAP_ARRAY2(char, len, F, CURRENT_PC); 61 _end_block = _first_free_entry + len; 62 } 63 entry = (BasicHashtableEntry<F>*)_first_free_entry; 64 _first_free_entry += _entry_size; 65 } 66 67 assert(_entry_size % HeapWordSize == 0, ""); 68 entry->set_hash(hashValue); 69 return entry; 70 } 71 72 73 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::new_entry(unsigned int hashValue, T obj) { 74 HashtableEntry<T, F>* entry; 75 76 entry = (HashtableEntry<T, F>*)BasicHashtable<F>::new_entry(hashValue); 77 entry->set_literal(obj); 78 return entry; 79 } 80 81 // Check to see if the hashtable is unbalanced. The caller set a flag to 82 // rehash at the next safepoint. If this bucket is 60 times greater than the 83 // expected average bucket length, it's an unbalanced hashtable. 84 // This is somewhat an arbitrary heuristic but if one bucket gets to 85 // rehash_count which is currently 100, there's probably something wrong. 86 87 template <class T, MEMFLAGS F> bool RehashableHashtable<T, F>::check_rehash_table(int count) { 88 assert(this->table_size() != 0, "underflow"); 89 if (count > (((double)this->number_of_entries()/(double)this->table_size())*rehash_multiple)) { 90 // Set a flag for the next safepoint, which should be at some guaranteed 91 // safepoint interval. 92 return true; 93 } 94 return false; 95 } 96 97 template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::_seed = 0; 98 99 // Create a new table and using alternate hash code, populate the new table 100 // with the existing elements. This can be used to change the hash code 101 // and could in the future change the size of the table. 102 103 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::move_to(RehashableHashtable<T, F>* new_table) { 104 105 // Initialize the global seed for hashing. 106 _seed = AltHashing::compute_seed(); 107 assert(seed() != 0, "shouldn't be zero"); 108 109 int saved_entry_count = this->number_of_entries(); 110 111 // Iterate through the table and create a new entry for the new table 112 for (int i = 0; i < new_table->table_size(); ++i) { 113 for (HashtableEntry<T, F>* p = this->bucket(i); p != NULL; ) { 114 HashtableEntry<T, F>* next = p->next(); 115 T string = p->literal(); 116 // Use alternate hashing algorithm on the symbol in the first table 117 unsigned int hashValue = string->new_hash(seed()); 118 // Get a new index relative to the new table (can also change size) 119 int index = new_table->hash_to_index(hashValue); 120 p->set_hash(hashValue); 121 // Keep the shared bit in the Hashtable entry to indicate that this entry 122 // can't be deleted. The shared bit is the LSB in the _next field so 123 // walking the hashtable past these entries requires 124 // BasicHashtableEntry::make_ptr() call. 125 bool keep_shared = p->is_shared(); 126 this->unlink_entry(p); 127 new_table->add_entry(index, p); 128 if (keep_shared) { 129 p->set_shared(); 130 } 131 p = next; 132 } 133 } 134 // give the new table the free list as well 135 new_table->copy_freelist(this); 136 assert(new_table->number_of_entries() == saved_entry_count, "lost entry on dictionary copy?"); 137 138 // Destroy memory used by the buckets in the hashtable. The memory 139 // for the elements has been used in a new table and is not 140 // destroyed. The memory reuse will benefit resizing the SystemDictionary 141 // to avoid a memory allocation spike at safepoint. 142 BasicHashtable<F>::free_buckets(); 143 } 144 145 template <MEMFLAGS F> void BasicHashtable<F>::free_buckets() { 146 if (NULL != _buckets) { 147 // Don't delete the buckets in the shared space. They aren't 148 // allocated by os::malloc 149 if (!UseSharedSpaces || 150 !FileMapInfo::current_info()->is_in_shared_space(_buckets)) { 151 FREE_C_HEAP_ARRAY(HashtableBucket, _buckets, F); 152 } 153 _buckets = NULL; 154 } 155 } 156 157 158 // Reverse the order of elements in the hash buckets. 159 160 template <MEMFLAGS F> void BasicHashtable<F>::reverse() { 161 162 for (int i = 0; i < _table_size; ++i) { 163 BasicHashtableEntry<F>* new_list = NULL; 164 BasicHashtableEntry<F>* p = bucket(i); 165 while (p != NULL) { 166 BasicHashtableEntry<F>* next = p->next(); 167 p->set_next(new_list); 168 new_list = p; 169 p = next; 170 } 171 *bucket_addr(i) = new_list; 172 } 173 } 174 175 176 // Copy the table to the shared space. 177 178 template <MEMFLAGS F> void BasicHashtable<F>::copy_table(char** top, char* end) { 179 180 // Dump the hash table entries. 181 182 intptr_t *plen = (intptr_t*)(*top); 183 *top += sizeof(*plen); 184 185 int i; 186 for (i = 0; i < _table_size; ++i) { 187 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr(); 188 *p != NULL; 189 p = (*p)->next_addr()) { 190 if (*top + entry_size() > end) { 191 report_out_of_shared_space(SharedMiscData); 192 } 193 *p = (BasicHashtableEntry<F>*)memcpy(*top, *p, entry_size()); 194 *top += entry_size(); 195 } 196 } 197 *plen = (char*)(*top) - (char*)plen - sizeof(*plen); 198 199 // Set the shared bit. 200 201 for (i = 0; i < _table_size; ++i) { 202 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) { 203 p->set_shared(); 204 } 205 } 206 } 207 208 209 210 // Reverse the order of elements in the hash buckets. 211 212 template <class T, MEMFLAGS F> void Hashtable<T, F>::reverse(void* boundary) { 213 214 for (int i = 0; i < this->table_size(); ++i) { 215 HashtableEntry<T, F>* high_list = NULL; 216 HashtableEntry<T, F>* low_list = NULL; 217 HashtableEntry<T, F>* last_low_entry = NULL; 218 HashtableEntry<T, F>* p = bucket(i); 219 while (p != NULL) { 220 HashtableEntry<T, F>* next = p->next(); 221 if ((void*)p->literal() >= boundary) { 222 p->set_next(high_list); 223 high_list = p; 224 } else { 225 p->set_next(low_list); 226 low_list = p; 227 if (last_low_entry == NULL) { 228 last_low_entry = p; 229 } 230 } 231 p = next; 232 } 233 if (low_list != NULL) { 234 *bucket_addr(i) = low_list; 235 last_low_entry->set_next(high_list); 236 } else { 237 *bucket_addr(i) = high_list; 238 } 239 } 240 } 241 242 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(Symbol *symbol) { 243 return symbol->size() * HeapWordSize; 244 } 245 246 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(oop oop) { 247 // NOTE: this would over-count if (pre-JDK8) java_lang_Class::has_offset_field() is true, 248 // and the String.value array is shared by several Strings. However, starting from JDK8, 249 // the String.value array is not shared anymore. 250 assert(oop != NULL && oop->klass() == SystemDictionary::String_klass(), "only strings are supported"); 251 return (oop->size() + java_lang_String::value(oop)->size()) * HeapWordSize; 252 } 253 254 // Dump footprint and bucket length statistics 255 // 256 // Note: if you create a new subclass of Hashtable<MyNewType, F>, you will need to 257 // add a new function Hashtable<T, F>::literal_size(MyNewType lit) 258 259 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::dump_table(outputStream* st, const char *table_name) { 260 NumberSeq summary; 261 int literal_bytes = 0; 262 for (int i = 0; i < this->table_size(); ++i) { 263 int count = 0; 264 for (HashtableEntry<T, F>* e = this->bucket(i); 265 e != NULL; e = e->next()) { 266 count++; 267 literal_bytes += literal_size(e->literal()); 268 } 269 summary.add((double)count); 270 } 271 double num_buckets = summary.num(); 272 double num_entries = summary.sum(); 273 274 int bucket_bytes = (int)num_buckets * sizeof(HashtableBucket<F>); 275 int entry_bytes = (int)num_entries * sizeof(HashtableEntry<T, F>); 276 int total_bytes = literal_bytes + bucket_bytes + entry_bytes; 277 278 double bucket_avg = (num_buckets <= 0) ? 0 : (bucket_bytes / num_buckets); 279 double entry_avg = (num_entries <= 0) ? 0 : (entry_bytes / num_entries); 280 double literal_avg = (num_entries <= 0) ? 0 : (literal_bytes / num_entries); 281 282 st->print_cr("%s statistics:", table_name); 283 st->print_cr("Number of buckets : %9d = %9d bytes, avg %7.3f", (int)num_buckets, bucket_bytes, bucket_avg); 284 st->print_cr("Number of entries : %9d = %9d bytes, avg %7.3f", (int)num_entries, entry_bytes, entry_avg); 285 st->print_cr("Number of literals : %9d = %9d bytes, avg %7.3f", (int)num_entries, literal_bytes, literal_avg); 286 st->print_cr("Total footprint : %9s = %9d bytes", "", total_bytes); 287 st->print_cr("Average bucket size : %9.3f", summary.avg()); 288 st->print_cr("Variance of bucket size : %9.3f", summary.variance()); 289 st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd()); 290 st->print_cr("Maximum bucket size : %9d", (int)summary.maximum()); 291 } 292 293 294 // Dump the hash table buckets. 295 296 template <MEMFLAGS F> void BasicHashtable<F>::copy_buckets(char** top, char* end) { 297 intptr_t len = _table_size * sizeof(HashtableBucket<F>); 298 *(intptr_t*)(*top) = len; 299 *top += sizeof(intptr_t); 300 301 *(intptr_t*)(*top) = _number_of_entries; 302 *top += sizeof(intptr_t); 303 304 if (*top + len > end) { 305 report_out_of_shared_space(SharedMiscData); 306 } 307 _buckets = (HashtableBucket<F>*)memcpy(*top, _buckets, len); 308 *top += len; 309 } 310 311 312 #ifndef PRODUCT 313 314 template <class T, MEMFLAGS F> void Hashtable<T, F>::print() { 315 ResourceMark rm; 316 317 for (int i = 0; i < BasicHashtable<F>::table_size(); i++) { 318 HashtableEntry<T, F>* entry = bucket(i); 319 while(entry != NULL) { 320 tty->print("%d : ", i); 321 entry->literal()->print(); 322 tty->cr(); 323 entry = entry->next(); 324 } 325 } 326 } 327 328 329 template <MEMFLAGS F> void BasicHashtable<F>::verify() { 330 int count = 0; 331 for (int i = 0; i < table_size(); i++) { 332 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) { 333 ++count; 334 } 335 } 336 assert(count == number_of_entries(), "number of hashtable entries incorrect"); 337 } 338 339 340 #endif // PRODUCT 341 342 343 #ifdef ASSERT 344 345 template <MEMFLAGS F> void BasicHashtable<F>::verify_lookup_length(double load) { 346 if ((double)_lookup_length / (double)_lookup_count > load * 2.0) { 347 warning("Performance bug: SystemDictionary lookup_count=%d " 348 "lookup_length=%d average=%lf load=%f", 349 _lookup_count, _lookup_length, 350 (double) _lookup_length / _lookup_count, load); 351 } 352 } 353 354 #endif 355 // Explicitly instantiate these types 356 template class Hashtable<ConstantPool*, mtClass>; 357 template class RehashableHashtable<Symbol*, mtSymbol>; 358 template class RehashableHashtable<oopDesc*, mtSymbol>; 359 template class Hashtable<Symbol*, mtSymbol>; 360 template class Hashtable<Klass*, mtClass>; 361 template class Hashtable<oop, mtClass>; 362 #if defined(SOLARIS) || defined(CHECK_UNHANDLED_OOPS) 363 template class Hashtable<oop, mtSymbol>; 364 template class RehashableHashtable<oop, mtSymbol>; 365 #endif // SOLARIS || CHECK_UNHANDLED_OOPS 366 template class Hashtable<oopDesc*, mtSymbol>; 367 template class Hashtable<Symbol*, mtClass>; 368 template class HashtableEntry<Symbol*, mtSymbol>; 369 template class HashtableEntry<Symbol*, mtClass>; 370 template class HashtableEntry<oop, mtSymbol>; 371 template class BasicHashtableEntry<mtSymbol>; 372 template class BasicHashtableEntry<mtCode>; 373 template class BasicHashtable<mtClass>; 374 template class BasicHashtable<mtSymbol>; 375 template class BasicHashtable<mtCode>; 376 template class BasicHashtable<mtInternal>;