/*

 * Copyright 1998-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 *

 */

// Recording and retrieval of oop relocations in compiled code.

class CodeBlob;

class OopRecorder : public ResourceObj {

 public:

  // A two-way mapping from positive indexes to oop handles.

  // The zero index is reserved for a constant (sharable) null.

  // Indexes may not be negative.

  // Use the given arena to manage storage, if not NULL.

  // By default, uses the current ResourceArea.

  OopRecorder(Arena* arena = NULL);

  // Generate a new index on which CodeBlob::oop_addr_at will work.

  // allocate_index and find_index never return the same index,

  // and allocate_index never returns the same index twice.

  // In fact, two successive calls to allocate_index return successive ints.

  int allocate_index(jobject h) {

    return add_handle(h, false);

  }

  // For a given jobject, this will return the same index repeatedly.

  // The index can later be given to oop_at to retrieve the oop.

  // However, the oop must not be changed via CodeBlob::oop_addr_at.

  int find_index(jobject h) {

    int index = maybe_find_index(h);

    if (index < 0) {  // previously unallocated

      index = add_handle(h, true);

    }

    return index;

  }

  // variant of find_index which does not allocate if not found (yields -1)

  int maybe_find_index(jobject h);

  // returns the size of the generated oop table, for sizing the CodeBlob.

  // must be called after all oops are allocated!

  int oop_size();

  // Retrieve the oop handle at a given index.

  jobject handle_at(int index);

  int element_count() {

    // there is always a NULL virtually present as first object

    return _handles->length() + first_index;

  }

  // copy the generated oop table to CodeBlob

  void copy_to(CodeBlob* code);  // => code->copy_oops(_handles)

  bool is_unused() { return _handles == NULL && !_complete; }

#ifdef ASSERT

  bool is_complete() { return _complete; }

#endif

 private:

  // leaky hash table of handle => index, to help detect duplicate insertion

  class IndexCache: public ResourceObj {

    // This class is only used by the OopRecorder class.

    friend class OopRecorder;

    enum {

      _log_cache_size = 9,

      _cache_size = (1<<_log_cache_size),

      // Index entries are ints.  The LSBit is a collision indicator.

      _collision_bit_shift = 0,

      _collision_bit = 1,

      _index_shift = _collision_bit_shift+1

    };

    int _cache[_cache_size];

    static juint cache_index(jobject handle) {

      juint ci = (int) (intptr_t) handle;

      ci ^= ci >> (BitsPerByte*2);

      ci += ci >> (BitsPerByte*1);

      return ci & (_cache_size-1);

    }

    int* cache_location(jobject handle) {

      return &_cache[ cache_index(handle) ];

    }

    static bool cache_location_collision(int* cloc) {

      return ((*cloc) & _collision_bit) != 0;

    }

    static int cache_location_index(int* cloc) {

      return (*cloc) >> _index_shift;

    }

    static void set_cache_location_index(int* cloc, int index) {

      int cval0 = (*cloc);

      int cval1 = (index << _index_shift);

      if (cval0 != 0 && cval1 != cval0)  cval1 += _collision_bit;

      (*cloc) = cval1;

    }

    IndexCache();

  };

  // Helper function; returns false for NULL or Universe::non_oop_word().

  inline bool is_real_jobject(jobject h);

  void maybe_initialize();

  int add_handle(jobject h, bool make_findable);

  enum { null_index = 0, first_index = 1, index_cache_threshold = 20 };

  GrowableArray<jobject>*   _handles;  // ordered list (first is always NULL)

  GrowableArray<int>*       _no_finds; // all unfindable indexes; usually empty

  IndexCache*               _indexes;  // map: jobject -> its probable index

  Arena*                    _arena;

  bool                      _complete;

#ifdef ASSERT

  static int _find_index_calls, _hit_indexes, _missed_indexes;

#endif

};