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 /*

  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

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 #ifndef SHARE_VM_UTILITIES_HASHTABLE_HPP

 #define SHARE_VM_UTILITIES_HASHTABLE_HPP

 #include "memory/allocation.hpp"

 #include "oops/oop.hpp"

 #include "oops/symbol.hpp"

 #include "runtime/handles.hpp"

 // This is a generic hashtable, designed to be used for the symbol

 // and string tables.

 //

 // It is implemented as an open hash table with a fixed number of buckets.

 //

 // %note:

 //  - TableEntrys are allocated in blocks to reduce the space overhead.

 class BasicHashtableEntry : public CHeapObj {

   friend class VMStructs;

 private:

   unsigned int         _hash;           // 32-bit hash for item

   // Link to next element in the linked list for this bucket.  EXCEPT

   // bit 0 set indicates that this entry is shared and must not be

   // unlinked from the table. Bit 0 is set during the dumping of the

   // archive. Since shared entries are immutable, _next fields in the

   // shared entries will not change.  New entries will always be

   // unshared and since pointers are align, bit 0 will always remain 0

   // with no extra effort.

   BasicHashtableEntry* _next;

   // Windows IA64 compiler requires subclasses to be able to access these

 protected:

   // Entry objects should not be created, they should be taken from the

   // free list with BasicHashtable.new_entry().

   BasicHashtableEntry() { ShouldNotReachHere(); }

   // Entry objects should not be destroyed.  They should be placed on

   // the free list instead with BasicHashtable.free_entry().

   ~BasicHashtableEntry() { ShouldNotReachHere(); }

 public:

   unsigned int hash() const             { return _hash; }

   void set_hash(unsigned int hash)      { _hash = hash; }

   unsigned int* hash_addr()             { return &_hash; }

   static BasicHashtableEntry* make_ptr(BasicHashtableEntry* p) {

     return (BasicHashtableEntry*)((intptr_t)p & -2);

   }

   BasicHashtableEntry* next() const {

     return make_ptr(_next);

   }

   void set_next(BasicHashtableEntry* next) {

     _next = next;

   }

   BasicHashtableEntry** next_addr() {

     return &_next;

   }

   bool is_shared() const {

     return ((intptr_t)_next & 1) != 0;

   }

   void set_shared() {

     _next = (BasicHashtableEntry*)((intptr_t)_next | 1);

   }

 };

 template <class T> class HashtableEntry : public BasicHashtableEntry {

   friend class VMStructs;

 private:

   T               _literal;          // ref to item in table.

 public:

   // Literal

   T literal() const                   { return _literal; }

   T* literal_addr()                   { return &_literal; }

   void set_literal(T s)               { _literal = s; }

   HashtableEntry* next() const {

     return (HashtableEntry*)BasicHashtableEntry::next();

   }

   HashtableEntry** next_addr() {

     return (HashtableEntry**)BasicHashtableEntry::next_addr();

   }

 };

 class HashtableBucket : public CHeapObj {

   friend class VMStructs;

 private:

   // Instance variable

   BasicHashtableEntry*       _entry;

 public:

   // Accessing

   void clear()                        { _entry = NULL; }

   // The following methods use order access methods to avoid race

   // conditions in multiprocessor systems.

   BasicHashtableEntry* get_entry() const;

   void set_entry(BasicHashtableEntry* l);

   // The following method is not MT-safe and must be done under lock.

   BasicHashtableEntry** entry_addr()  { return &_entry; }

 };

 class BasicHashtable : public CHeapObj {

   friend class VMStructs;

 public:

   BasicHashtable(int table_size, int entry_size);

   BasicHashtable(int table_size, int entry_size,

                  HashtableBucket* buckets, int number_of_entries);

   // Sharing support.

   void copy_buckets(char** top, char* end);

   void copy_table(char** top, char* end);

   // Bucket handling

   int hash_to_index(unsigned int full_hash) {

     int h = full_hash % _table_size;

     assert(h >= 0 && h < _table_size, "Illegal hash value");

     return h;

   }

   // Reverse the order of elements in each of the buckets.

   void reverse();

   static unsigned int hash_symbol(const char* s, int len);

 private:

   // Instance variables

   int               _table_size;

   HashtableBucket*  _buckets;

   BasicHashtableEntry* _free_list;

   char*             _first_free_entry;

   char*             _end_block;

   int               _entry_size;

   int               _number_of_entries;

 protected:

 #ifdef ASSERT

   int               _lookup_count;

   int               _lookup_length;

   void verify_lookup_length(double load);

 #endif

   void initialize(int table_size, int entry_size, int number_of_entries);

   // Accessor

   int entry_size() const { return _entry_size; }

   int table_size() { return _table_size; }

   // The following method is MT-safe and may be used with caution.

   BasicHashtableEntry* bucket(int i);

   // The following method is not MT-safe and must be done under lock.

   BasicHashtableEntry** bucket_addr(int i) { return _buckets[i].entry_addr(); }

   // Table entry management

   BasicHashtableEntry* new_entry(unsigned int hashValue);

 public:

   void set_entry(int index, BasicHashtableEntry* entry);

   void add_entry(int index, BasicHashtableEntry* entry);

   void free_entry(BasicHashtableEntry* entry);

   int number_of_entries() { return _number_of_entries; }

   void verify() PRODUCT_RETURN;

 };

 template <class T> class Hashtable : public BasicHashtable {

   friend class VMStructs;

 public:

   Hashtable(int table_size, int entry_size)

     : BasicHashtable(table_size, entry_size) { }

   Hashtable(int table_size, int entry_size,

                    HashtableBucket* buckets, int number_of_entries)

     : BasicHashtable(table_size, entry_size, buckets, number_of_entries) { }

   // Debugging

   void print()               PRODUCT_RETURN;

   // Reverse the order of elements in each of the buckets. Hashtable

   // entries which refer to objects at a lower address than 'boundary'

   // are separated from those which refer to objects at higher

   // addresses, and appear first in the list.

   void reverse(void* boundary = NULL);

 protected:

   unsigned int compute_hash(Symbol* name) {

     return (unsigned int) name->identity_hash();

   }

   int index_for(Symbol* name) {

     return hash_to_index(compute_hash(name));

   }

   // Table entry management

   HashtableEntry<T>* new_entry(unsigned int hashValue, T obj);

   // The following method is MT-safe and may be used with caution.

   HashtableEntry<T>* bucket(int i) {

     return (HashtableEntry<T>*)BasicHashtable::bucket(i);

   }

   // The following method is not MT-safe and must be done under lock.

   HashtableEntry<T>** bucket_addr(int i) {

     return (HashtableEntry<T>**)BasicHashtable::bucket_addr(i);

   }

 };

 //  Verions of hashtable where two handles are used to compute the index.

 template <class T> class TwoOopHashtable : public Hashtable<T> {

   friend class VMStructs;

 protected:

   TwoOopHashtable(int table_size, int entry_size)

     : Hashtable<T>(table_size, entry_size) {}

   TwoOopHashtable(int table_size, int entry_size, HashtableBucket* t,

                   int number_of_entries)

     : Hashtable<T>(table_size, entry_size, t, number_of_entries) {}

 public:

   unsigned int compute_hash(Symbol* name, Handle loader) {

     // Be careful with identity_hash(), it can safepoint and if this

     // were one expression, the compiler could choose to unhandle each

     // oop before calling identity_hash() for either of them.  If the first

     // causes a GC, the next would fail.

     unsigned int name_hash = name->identity_hash();

     unsigned int loader_hash = loader.is_null() ? 0 : loader->identity_hash();

     return name_hash ^ loader_hash;

   }

   int index_for(Symbol* name, Handle loader) {

     return hash_to_index(compute_hash(name, loader));

   }

 };

 #endif // SHARE_VM_UTILITIES_HASHTABLE_HPP