~drizzle-trunk/drizzle/development

/* Copyright (C) 2005 MySQL AB

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

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; version 2 of the License.

   This program 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 for more details.

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

   along with this program; if not, write to the Free Software

   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

#ifndef TABLE_MAPPING_H

#define TABLE_MAPPING_H

/* Forward declarations */

class Table;

/*

  CLASS table_mapping

  RESPONSIBILITIES

    The table mapping is used to map table id's to table pointers

  COLLABORATION

    RELAY_LOG    For mapping table id:s to tables when receiving events.

 */

/*

  Guilhem to Mats:

  in the table_mapping class, the memory is allocated and never freed (until

  destruction). So this is a good candidate for allocating inside a MEM_ROOT:

  it gives the efficient allocation in chunks (like in expand()). So I have

  introduced a MEM_ROOT.

  Note that inheriting from Sql_alloc had no effect: it has effects only when

  "ptr= new table_mapping" is called, and this is never called. And it would

  then allocate from thd->mem_root which is a highly volatile object (reset

  from example after executing each query, see dispatch_command(), it has a

  free_root() at end); as the table_mapping object is supposed to live longer

  than a query, it was dangerous.

  A dedicated MEM_ROOT needs to be used, see below.

*/

class table_mapping {

private:

  MEM_ROOT m_mem_root;

public:

  enum enum_error {

      ERR_NO_ERROR = 0,

      ERR_LIMIT_EXCEEDED,

      ERR_MEMORY_ALLOCATION

  };

  table_mapping();

  ~table_mapping();

  Table* get_table(ulong table_id);

  int       set_table(ulong table_id, Table* table);

  int       remove_table(ulong table_id);

  void      clear_tables();

  ulong     count() const { return m_table_ids.records; }

private:

  /*

    This is a POD (Plain Old Data).  Keep it that way (we apply offsetof() to

    it, which only works for PODs)

  */

  struct entry { 

    ulong table_id;

    union {

      Table *table;

      entry *next;

    };

  };

  entry *find_entry(ulong table_id)

  {

    return (entry *)hash_search(&m_table_ids,

				(uchar*)&table_id,

				sizeof(table_id));

  }

  int expand();

  /*

    Head of the list of free entries; "free" in the sense that it's an

    allocated entry free for use, NOT in the sense that it's freed

    memory.

  */

  entry *m_free;

  /* Correspondance between an id (a number) and a Table object */

  HASH m_table_ids;

};

#endif