Per Heikki's request make trans_register_ha tolerant to multiple registrations

    "beginning of transaction" and "beginning of statement").

    Only storage engines registered for the transaction/statement

    will know when to commit/rollback it.

  NOTE

    trans_register_ha is idempotent - storage engine may register many

    times per transaction.

*/

void trans_register_ha(THD *thd, bool all, handlerton *ht_arg)

{

  THD_TRANS *trans;

  handlerton **ht;

  DBUG_ENTER("trans_register_ha");

  DBUG_PRINT("enter",("%s", all ? "all" : "stmt"));

  else

    trans= &thd->transaction.stmt;

#ifndef DBUG_OFF

  handlerton **ht=trans->ht;

  while (*ht)

  {

    DBUG_ASSERT(*ht != ht_arg);

    ht++;

  }

#endif

  for (ht=trans->ht; *ht; ht++)

    if (*ht == ht_arg)

      DBUG_VOID_RETURN;

  trans->ht[trans->nht++]=ht_arg;

  DBUG_ASSERT(*ht == ht_arg);

  trans->no_2pc|=(ht_arg->prepare==0);

  if (thd->transaction.xid.is_null())

    thd->transaction.xid.set(thd->query_id);