/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
 *  vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
 *
 *  Copyright (C) 2008 Sun Microsystems
 *
 *  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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef DRIZZLED_HA_TRX_INFO_H
#define DRIZZLED_HA_TRX_INFO_H

/**
  Either statement transaction or normal transaction - related
  thread-specific storage engine data.

  If a storage engine participates in a statement/transaction,
  an instance of this class is present in
  session->transaction.{stmt|all}.ha_list. The addition to
  {stmt|all}.ha_list is made by trans_register_ha().

  When it's time to commit or rollback, each element of ha_list
  is used to access storage engine's prepare()/commit()/rollback()
  methods, and also to evaluate if a full two phase commit is
  necessary.

  @sa General description of transaction handling in handler.cc.
*/

class Ha_trx_info
{
public:
  /** Register this storage engine in the given transaction context. */
  void register_ha(Session_TRANS *trans, handlerton *ht_arg)
  {
    assert(m_flags == 0);
    assert(m_ht == NULL);
    assert(m_next == NULL);

    m_ht= ht_arg;
    m_flags= (int) TRX_READ_ONLY; /* Assume read-only at start. */

    m_next= trans->ha_list;
    trans->ha_list= this;
  }

  /** Clear, prepare for reuse. */
  void reset()
  {
    m_next= NULL;
    m_ht= NULL;
    m_flags= 0;
  }

  Ha_trx_info() { reset(); }

  void set_trx_read_write()
  {
    assert(is_started());
    m_flags|= (int) TRX_READ_WRITE;
  }
  bool is_trx_read_write() const
  {
    assert(is_started());
    return m_flags & (int) TRX_READ_WRITE;
  }
  bool is_started() const { return m_ht != NULL; }
  /** Mark this transaction read-write if the argument is read-write. */
  void coalesce_trx_with(const Ha_trx_info *stmt_trx)
  {
    /*
      Must be called only after the transaction has been started.
      Can be called many times, e.g. when we have many
      read-write statements in a transaction.
    */
    assert(is_started());
    if (stmt_trx->is_trx_read_write())
      set_trx_read_write();
  }
  Ha_trx_info *next() const
  {
    assert(is_started());
    return m_next;
  }
  handlerton *ht() const
  {
    assert(is_started());
    return m_ht;
  }
private:
  enum { TRX_READ_ONLY= 0, TRX_READ_WRITE= 1 };
  /** Auxiliary, used for ha_list management */
  Ha_trx_info *m_next;
  /**
    Although a given Ha_trx_info instance is currently always used
    for the same storage engine, 'ht' is not-NULL only when the
    corresponding storage is a part of a transaction.
  */
  handlerton *m_ht;
  /**
    Transaction flags related to this engine.
    Not-null only if this instance is a part of transaction.
    May assume a combination of enum values above.
  */
  unsigned char       m_flags;
};

#endif /* DRIZZLED_HA_TRX_INFO_H */