/*

 * Copyright (c) 2003, 2005, 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

 * questions.

 *

 */

// 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);

  }

};

class HashtableEntry : public BasicHashtableEntry {

  friend class VMStructs;

private:

  oop               _literal;          // ref to item in table.

public:

  // Literal

  oop literal() const                   { return _literal; }

  oop* literal_addr()                   { return &_literal; }

  void set_literal(oop 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();

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;

};

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) { }

  // Invoke "f->do_oop" on the locations of all oops in the table.

  void oops_do(OopClosure* f);

  // Debugging

  void print()               PRODUCT_RETURN;

  // GC support

  //   Delete pointers to otherwise-unreachable objects.

  void unlink(BoolObjectClosure* cl);

  // 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:

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

  unsigned int compute_hash(symbolHandle name) {

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

  }

  int index_for(symbolHandle name) {

    return hash_to_index(compute_hash(name));

  }

  // Table entry management

  HashtableEntry* new_entry(unsigned int hashValue, oop obj);

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

  HashtableEntry* bucket(int i) {

    return (HashtableEntry*)BasicHashtable::bucket(i);

  }

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

  HashtableEntry** bucket_addr(int i) {

    return (HashtableEntry**)BasicHashtable::bucket_addr(i);

  }

};

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

class TwoOopHashtable : public Hashtable {

  friend class VMStructs;

protected:

  TwoOopHashtable(int table_size, int entry_size)

    : Hashtable(table_size, entry_size) {}

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

                  int number_of_entries)

    : Hashtable(table_size, entry_size, t, number_of_entries) {}

public:

  unsigned int compute_hash(symbolHandle 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(symbolHandle name, Handle loader) {

    return hash_to_index(compute_hash(name, loader));

  }

};