Method call_in_target_thread

sql/sql_show.cc:3179–3213

*/

void Show_explain_request::call_in_target_thread()
{
  Query_arena backup_arena;
  bool printed_anything= FALSE;

  /* 
    Change the arena because JOIN::print_explain and co. are going to allocate
    items. Let them allocate them on our arena.
  */
  target_thd->set_n_backup_active_arena((Query_arena*)request_thd,
                                        &backup_arena);

  query_str.copy(target_thd->query(),
                 target_thd->query_length(),
                 target_thd->query_charset());

  DBUG_ASSERT(current_thd == target_thd);

  /*
    When producing JSON output, one should not change current_thd.
    (If one does that, they will hit an assert when printing constant item
    fields).
  */
  if (target_thd->lex->print_explain(explain_buf, 0 /* explain flags*/,
                                     is_analyze, is_json_format,
                                     &printed_anything))
  {
    failed_to_produce= TRUE;
  }

  if (!printed_anything)
    failed_to_produce= TRUE;

  target_thd->restore_active_arena((Query_arena*)request_thd, &backup_arena);
}


int select_result_explain_buffer::send_data(List<Item> &items)