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 #ifndef SHARE_VM_UTILITIES_HASHTABLE_HPP
  26 #define SHARE_VM_UTILITIES_HASHTABLE_HPP
  27 
  28 #include "classfile/classLoaderData.hpp"
  29 #include "memory/allocation.hpp"
  30 #include "oops/oop.hpp"
  31 #include "oops/symbol.hpp"
  32 #include "runtime/handles.hpp"
  33 
  34 // This is a generic hashtable, designed to be used for the symbol
  35 // and string tables.
  36 //
  37 // It is implemented as an open hash table with a fixed number of buckets.
  38 //
  39 // %note:
  40 //  - TableEntrys are allocated in blocks to reduce the space overhead.
  41 
  42 
  43 
  44 template <MEMFLAGS F> class BasicHashtableEntry : public CHeapObj<F> {
  45   friend class VMStructs;
  46 private:
  47   unsigned int         _hash;           // 32-bit hash for item
  48 
  49   // Link to next element in the linked list for this bucket.  EXCEPT
  50   // bit 0 set indicates that this entry is shared and must not be
  51   // unlinked from the table. Bit 0 is set during the dumping of the
  52   // archive. Since shared entries are immutable, _next fields in the
  53   // shared entries will not change.  New entries will always be
  54   // unshared and since pointers are align, bit 0 will always remain 0
  55   // with no extra effort.
  56   BasicHashtableEntry<F>* _next;
  57 
  58   // Windows IA64 compiler requires subclasses to be able to access these
  59 protected:
  60   // Entry objects should not be created, they should be taken from the
  61   // free list with BasicHashtable.new_entry().
  62   BasicHashtableEntry()  { guarantee(false, "Should not be called"); }
  63   // Entry objects should not be destroyed.  They should be placed on
  64   // the free list instead with BasicHashtable.free_entry().
  65   ~BasicHashtableEntry() { guarantee(false, "Should not be called"); }
  66 
  67 public:
  68 
  69   unsigned int hash() const             { return _hash; }
  70   void set_hash(unsigned int hash)      { _hash = hash; }
  71   unsigned int* hash_addr()             { return &_hash; }
  72 
  73   static BasicHashtableEntry<F>* make_ptr(BasicHashtableEntry<F>* p) {
  74     return (BasicHashtableEntry*)((intptr_t)p & -2);
  75   }
  76 
  77   BasicHashtableEntry<F>* next() const {
  78     return make_ptr(_next);
  79   }
  80 
  81   void set_next(BasicHashtableEntry<F>* next) {
  82     _next = next;
  83   }
  84 
  85   BasicHashtableEntry<F>** next_addr() {
  86     return &_next;
  87   }
  88 
  89   bool is_shared() const {
  90     return ((intptr_t)_next & 1) != 0;
  91   }
  92 
  93   void set_shared() {
  94     _next = (BasicHashtableEntry<F>*)((intptr_t)_next | 1);
  95   }
  96 };
  97 
  98 
  99 
 100 template <class T, MEMFLAGS F> class HashtableEntry : public BasicHashtableEntry<F> {
 101   friend class VMStructs;
 102 private:
 103   T               _literal;          // ref to item in table.
 104 
 105 public:
 106   // Literal
 107   T literal() const                   { return _literal; }
 108   T* literal_addr()                   { return &_literal; }
 109   void set_literal(T s)               { _literal = s; }
 110 
 111   HashtableEntry* next() const {
 112     return (HashtableEntry*)BasicHashtableEntry<F>::next();
 113   }
 114   HashtableEntry** next_addr() {
 115     return (HashtableEntry**)BasicHashtableEntry<F>::next_addr();
 116   }
 117 };
 118 
 119 
 120 
 121 template <MEMFLAGS F> class HashtableBucket : public CHeapObj<F> {
 122   friend class VMStructs;
 123 private:
 124   // Instance variable
 125   BasicHashtableEntry<F>*       _entry;
 126 
 127 public:
 128   // Accessing
 129   void clear()                        { _entry = NULL; }
 130 
 131   // The following methods use order access methods to avoid race
 132   // conditions in multiprocessor systems.
 133   BasicHashtableEntry<F>* get_entry() const;
 134   void set_entry(BasicHashtableEntry<F>* l);
 135 
 136   // The following method is not MT-safe and must be done under lock.
 137   BasicHashtableEntry<F>** entry_addr()  { return &_entry; }
 138 };
 139 
 140 
 141 template <MEMFLAGS F> class BasicHashtable : public CHeapObj<F> {
 142   friend class VMStructs;
 143 
 144 public:
 145   BasicHashtable(int table_size, int entry_size);
 146   BasicHashtable(int table_size, int entry_size,
 147                  HashtableBucket<F>* buckets, int number_of_entries);
 148 
 149   // Sharing support.
 150   void copy_buckets(char** top, char* end);
 151   void copy_table(char** top, char* end);
 152 
 153   // Bucket handling
 154   int hash_to_index(unsigned int full_hash) {
 155     int h = full_hash % _table_size;
 156     assert(h >= 0 && h < _table_size, "Illegal hash value");
 157     return h;
 158   }
 159 
 160   // Reverse the order of elements in each of the buckets.
 161   void reverse();
 162 
 163 private:
 164   // Instance variables
 165   int               _table_size;
 166   HashtableBucket<F>*     _buckets;
 167   BasicHashtableEntry<F>* _free_list;
 168   char*             _first_free_entry;
 169   char*             _end_block;
 170   int               _entry_size;
 171   int               _number_of_entries;
 172 
 173 protected:
 174 
 175 #ifdef ASSERT
 176   int               _lookup_count;
 177   int               _lookup_length;
 178   void verify_lookup_length(double load);
 179 #endif
 180 
 181   void initialize(int table_size, int entry_size, int number_of_entries);
 182 
 183   // Accessor
 184   int entry_size() const { return _entry_size; }
 185 
 186   // The following method is MT-safe and may be used with caution.
 187   BasicHashtableEntry<F>* bucket(int i);
 188 
 189   // The following method is not MT-safe and must be done under lock.
 190   BasicHashtableEntry<F>** bucket_addr(int i) { return _buckets[i].entry_addr(); }
 191 
 192   // Attempt to get an entry from the free list
 193   BasicHashtableEntry<F>* new_entry_free_list();
 194 
 195   // Table entry management
 196   BasicHashtableEntry<F>* new_entry(unsigned int hashValue);
 197 
 198   // Used when moving the entry to another table
 199   // Clean up links, but do not add to free_list
 200   void unlink_entry(BasicHashtableEntry<F>* entry) {
 201     entry->set_next(NULL);
 202     --_number_of_entries;
 203   }
 204 
 205   // Move over freelist and free block for allocation
 206   void copy_freelist(BasicHashtable* src) {
 207     _free_list = src->_free_list;
 208     src->_free_list = NULL;
 209     _first_free_entry = src->_first_free_entry;
 210     src->_first_free_entry = NULL;
 211     _end_block = src->_end_block;
 212     src->_end_block = NULL;
 213   }
 214 
 215   // Free the buckets in this hashtable
 216   void free_buckets();
 217 
 218 public:
 219   int table_size() { return _table_size; }
 220   void set_entry(int index, BasicHashtableEntry<F>* entry);
 221 
 222   void add_entry(int index, BasicHashtableEntry<F>* entry);
 223 
 224   void free_entry(BasicHashtableEntry<F>* entry);
 225 
 226   int number_of_entries() { return _number_of_entries; }
 227 
 228   void verify() PRODUCT_RETURN;
 229 };
 230 
 231 
 232 template <class T, MEMFLAGS F> class Hashtable : public BasicHashtable<F> {
 233   friend class VMStructs;
 234 
 235 public:
 236   Hashtable(int table_size, int entry_size)
 237     : BasicHashtable<F>(table_size, entry_size) { }
 238 
 239   Hashtable(int table_size, int entry_size,
 240                    HashtableBucket<F>* buckets, int number_of_entries)
 241     : BasicHashtable<F>(table_size, entry_size, buckets, number_of_entries) { }
 242 
 243   // Debugging
 244   void print()               PRODUCT_RETURN;
 245 
 246   // Reverse the order of elements in each of the buckets. Hashtable
 247   // entries which refer to objects at a lower address than 'boundary'
 248   // are separated from those which refer to objects at higher
 249   // addresses, and appear first in the list.
 250   void reverse(void* boundary = NULL);
 251 
 252 protected:
 253 
 254   unsigned int compute_hash(Symbol* name) {
 255     return (unsigned int) name->identity_hash();
 256   }
 257 
 258   int index_for(Symbol* name) {
 259     return this->hash_to_index(compute_hash(name));
 260   }
 261 
 262   // Table entry management
 263   HashtableEntry<T, F>* new_entry(unsigned int hashValue, T obj);
 264 
 265   // The following method is MT-safe and may be used with caution.
 266   HashtableEntry<T, F>* bucket(int i) {
 267     return (HashtableEntry<T, F>*)BasicHashtable<F>::bucket(i);
 268   }
 269 
 270   // The following method is not MT-safe and must be done under lock.
 271   HashtableEntry<T, F>** bucket_addr(int i) {
 272     return (HashtableEntry<T, F>**)BasicHashtable<F>::bucket_addr(i);
 273   }
 274 
 275 };
 276 
 277 template <class T, MEMFLAGS F> class RehashableHashtable : public Hashtable<T, F> {
 278  protected:
 279 
 280   enum {
 281     rehash_count = 100,
 282     rehash_multiple = 60
 283   };
 284 
 285   // Check that the table is unbalanced
 286   bool check_rehash_table(int count);
 287 
 288  public:
 289   RehashableHashtable(int table_size, int entry_size)
 290     : Hashtable<T, F>(table_size, entry_size) { }
 291 
 292   RehashableHashtable(int table_size, int entry_size,
 293                    HashtableBucket<F>* buckets, int number_of_entries)
 294     : Hashtable<T, F>(table_size, entry_size, buckets, number_of_entries) { }
 295 
 296 
 297   // Function to move these elements into the new table.
 298   void move_to(RehashableHashtable<T, F>* new_table);
 299   static bool use_alternate_hashcode()  { return _seed != 0; }
 300   static juint seed()                    { return _seed; }
 301 
 302   static int literal_size(Symbol *symbol);
 303   static int literal_size(oop oop);
 304 
 305   // The following two are currently not used, but are needed anyway because some
 306   // C++ compilers (MacOS and Solaris) force the instantiation of
 307   // Hashtable<ConstantPool*, mtClass>::dump_table() even though we never call this function
 308   // in the VM code.
 309   static int literal_size(ConstantPool *cp) {Unimplemented(); return 0;}
 310   static int literal_size(Klass *k)         {Unimplemented(); return 0;}
 311 
 312   void dump_table(outputStream* st, const char *table_name);
 313 
 314  private:
 315   static juint _seed;
 316 };
 317 
 318 
 319 // Versions of hashtable where two handles are used to compute the index.
 320 
 321 template <class T, MEMFLAGS F> class TwoOopHashtable : public Hashtable<T, F> {
 322   friend class VMStructs;
 323 protected:
 324   TwoOopHashtable(int table_size, int entry_size)
 325     : Hashtable<T, F>(table_size, entry_size) {}
 326 
 327   TwoOopHashtable(int table_size, int entry_size, HashtableBucket<F>* t,
 328                   int number_of_entries)
 329     : Hashtable<T, F>(table_size, entry_size, t, number_of_entries) {}
 330 
 331 public:
 332   unsigned int compute_hash(Symbol* name, ClassLoaderData* loader_data) {
 333     unsigned int name_hash = name->identity_hash();
 334     // loader is null with CDS
 335     assert(loader_data != NULL || UseSharedSpaces || DumpSharedSpaces,
 336            "only allowed with shared spaces");
 337     unsigned int loader_hash = loader_data == NULL ? 0 : loader_data->identity_hash();
 338     return name_hash ^ loader_hash;
 339   }
 340 
 341   int index_for(Symbol* name, ClassLoaderData* loader_data) {
 342     return this->hash_to_index(compute_hash(name, loader_data));
 343   }
 344 };
 345 
 346 #endif // SHARE_VM_UTILITIES_HASHTABLE_HPP