1 /*
   2  * Copyright (c) 2003, 2017, 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() { ShouldNotReachHere(); }
  63   // Entry objects should not be destroyed.  They should be placed on
  64   // the free list instead with BasicHashtable.free_entry().
  65   ~BasicHashtableEntry() { ShouldNotReachHere(); }
  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 
 142 template <MEMFLAGS F> class BasicHashtable : public CHeapObj<F> {
 143   friend class VMStructs;
 144 
 145 public:
 146   BasicHashtable(int table_size, int entry_size);
 147   BasicHashtable(int table_size, int entry_size,
 148                  HashtableBucket<F>* buckets, int number_of_entries);
 149 
 150   // Sharing support.
 151   size_t count_bytes_for_buckets();
 152   size_t count_bytes_for_table();
 153   void copy_buckets(char* top, char* end);
 154   void copy_table(char* top, char* end);
 155 
 156   // Bucket handling
 157   int hash_to_index(unsigned int full_hash) const {
 158     int h = full_hash % _table_size;
 159     assert(h >= 0 && h < _table_size, "Illegal hash value");
 160     return h;
 161   }
 162 
 163 private:
 164   // Instance variables
 165   int               _table_size;
 166   HashtableBucket<F>*     _buckets;
 167   BasicHashtableEntry<F>* volatile _free_list;
 168   char*             _first_free_entry;
 169   char*             _end_block;
 170   int               _entry_size;
 171   volatile int      _number_of_entries;
 172 
 173 protected:
 174 
 175   void initialize(int table_size, int entry_size, int number_of_entries);
 176 
 177   // Accessor
 178   int entry_size() const { return _entry_size; }
 179 
 180   // The following method is MT-safe and may be used with caution.
 181   BasicHashtableEntry<F>* bucket(int i) const;
 182 
 183   // The following method is not MT-safe and must be done under lock.
 184   BasicHashtableEntry<F>** bucket_addr(int i) { return _buckets[i].entry_addr(); }
 185 
 186   // Attempt to get an entry from the free list
 187   BasicHashtableEntry<F>* new_entry_free_list();
 188 
 189   // Table entry management
 190   BasicHashtableEntry<F>* new_entry(unsigned int hashValue);
 191 
 192   // Used when moving the entry to another table
 193   // Clean up links, but do not add to free_list
 194   void unlink_entry(BasicHashtableEntry<F>* entry) {
 195     entry->set_next(NULL);
 196     --_number_of_entries;
 197   }
 198 
 199   // Move over freelist and free block for allocation
 200   void copy_freelist(BasicHashtable* src) {
 201     _free_list = src->_free_list;
 202     src->_free_list = NULL;
 203     _first_free_entry = src->_first_free_entry;
 204     src->_first_free_entry = NULL;
 205     _end_block = src->_end_block;
 206     src->_end_block = NULL;
 207   }
 208 
 209   // Free the buckets in this hashtable
 210   void free_buckets();
 211 
 212   // Helper data structure containing context for the bucket entry unlink process,
 213   // storing the unlinked buckets in a linked list.
 214   // Also avoids the need to pass around these four members as parameters everywhere.
 215   struct BucketUnlinkContext {
 216     int _num_processed;
 217     int _num_removed;
 218     // Head and tail pointers for the linked list of removed entries.
 219     BasicHashtableEntry<F>* _removed_head;
 220     BasicHashtableEntry<F>* _removed_tail;
 221 
 222     BucketUnlinkContext() : _num_processed(0), _num_removed(0), _removed_head(NULL), _removed_tail(NULL) {
 223     }
 224 
 225     void free_entry(BasicHashtableEntry<F>* entry);
 226   };
 227   // Add of bucket entries linked together in the given context to the global free list. This method
 228   // is mt-safe wrt. to other calls of this method.
 229   void bulk_free_entries(BucketUnlinkContext* context);
 230 public:
 231   int table_size() const { return _table_size; }
 232   void set_entry(int index, BasicHashtableEntry<F>* entry);
 233 
 234   void add_entry(int index, BasicHashtableEntry<F>* entry);
 235 
 236   void free_entry(BasicHashtableEntry<F>* entry);
 237 
 238   int number_of_entries() const { return _number_of_entries; }
 239 
 240   bool resize(int new_size);
 241 
 242   template <class T> void verify_table(const char* table_name) PRODUCT_RETURN;
 243 };
 244 
 245 
 246 template <class T, MEMFLAGS F> class Hashtable : public BasicHashtable<F> {
 247   friend class VMStructs;
 248 
 249 public:
 250   Hashtable(int table_size, int entry_size)
 251     : BasicHashtable<F>(table_size, entry_size) { }
 252 
 253   Hashtable(int table_size, int entry_size,
 254                    HashtableBucket<F>* buckets, int number_of_entries)
 255     : BasicHashtable<F>(table_size, entry_size, buckets, number_of_entries) { }
 256 
 257   // Debugging
 258   void print()               PRODUCT_RETURN;
 259 
 260   unsigned int compute_hash(const Symbol* name) const {
 261     return (unsigned int) name->identity_hash();
 262   }
 263 
 264   int index_for(const Symbol* name) const {
 265     return this->hash_to_index(compute_hash(name));
 266   }
 267 
 268   void print_table_statistics(outputStream* st, const char *table_name);
 269 
 270  protected:
 271 
 272   // Table entry management
 273   HashtableEntry<T, F>* new_entry(unsigned int hashValue, T obj);
 274   // Don't create and use freelist of HashtableEntry.
 275   HashtableEntry<T, F>* allocate_new_entry(unsigned int hashValue, T obj);
 276 
 277   // The following method is MT-safe and may be used with caution.
 278   HashtableEntry<T, F>* bucket(int i) const {
 279     return (HashtableEntry<T, F>*)BasicHashtable<F>::bucket(i);
 280   }
 281 
 282   // The following method is not MT-safe and must be done under lock.
 283   HashtableEntry<T, F>** bucket_addr(int i) {
 284     return (HashtableEntry<T, F>**)BasicHashtable<F>::bucket_addr(i);
 285   }

 286 };
 287 
 288 template <class T, MEMFLAGS F> class RehashableHashtable : public Hashtable<T, F> {
 289  friend class VMStructs;
 290  protected:
 291 
 292   enum {
 293     rehash_count = 100,
 294     rehash_multiple = 60
 295   };
 296 
 297   // Check that the table is unbalanced
 298   bool check_rehash_table(int count);
 299 
 300  public:
 301   RehashableHashtable(int table_size, int entry_size)
 302     : Hashtable<T, F>(table_size, entry_size) { }
 303 
 304   RehashableHashtable(int table_size, int entry_size,
 305                    HashtableBucket<F>* buckets, int number_of_entries)
 306     : Hashtable<T, F>(table_size, entry_size, buckets, number_of_entries) { }
 307 
 308 
 309   // Function to move these elements into the new table.
 310   void move_to(RehashableHashtable<T, F>* new_table);
 311   static bool use_alternate_hashcode();
 312   static juint seed();
 313 
 314  private:
 315   static juint _seed;
 316 };
 317 
 318 template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::_seed = 0;
 319 template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::seed() { return _seed; };
 320 template <class T, MEMFLAGS F> bool  RehashableHashtable<T, F>::use_alternate_hashcode() { return _seed != 0; };
 321 
 322 #endif // SHARE_VM_UTILITIES_HASHTABLE_HPP
--- EOF ---