lb_leastloaded.cpp

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            }
        }
      ACE_CATCH (CosLoadBalancing::LocationNotFound, ex)
        {
          // No load available for the requested location.  Try the
          // next location.
        }
      ACE_ENDTRY;
      ACE_CHECK;
    }
}

PortableServer::POA_ptr
TAO_LB_LeastLoaded::_default_POA (ACE_ENV_SINGLE_ARG_DECL_NOT_USED)
{
  return PortableServer::POA::_duplicate (this->poa_.in ());
}

CORBA::Boolean
TAO_LB_LeastLoaded::get_location (
  CosLoadBalancing::LoadManager_ptr load_manager,
  const PortableGroup::Locations & locations,
  PortableGroup::Location & location
  ACE_ENV_ARG_DECL)
{
  CORBA::Float min_load = FLT_MAX;  // Start out with the largest
                                    // positive value.

  CORBA::ULong location_index = 0;
  CORBA::Boolean found_location = 0;
  CORBA::Boolean found_load = 0;

  const CORBA::ULong len = locations.length ();

  // Iterate through the entire location list to find the least loaded
  // of them.
  for (CORBA::ULong i = 0; i < len; ++i)
    {
      ACE_TRY
        {
          const PortableGroup::Location & loc = locations[i];

          // Retrieve the load list for the location from the LoadManager
          // and push it to this Strategy's load processor.
          CosLoadBalancing::LoadList_var current_loads =
            load_manager->get_loads (loc
                                     ACE_ENV_ARG_PARAMETER);
          ACE_TRY_CHECK;

          found_load = 1;

          CosLoadBalancing::Load load;
          this->push_loads (loc,
                            current_loads.in (),
                            load
                            ACE_ENV_ARG_PARAMETER);
          ACE_TRY_CHECK;

//           ACE_DEBUG ((LM_DEBUG,
//                       "LOC = %u"
//                       "\tC = %d"
//                       "\treject = %f"
//                       "\tload = %f\n"
//                       "\tmin_load = %f\n",
//                       i,
//                       (this->reject_threshold_ == 0
//                        || load.value < this->reject_threshold_),
//                       this->reject_threshold_,
//                       load.value,
//                       min_load));

          if ((this->reject_threshold_ == 0
               || load.value < this->reject_threshold_)
              && load.value < min_load)
            {
//               ACE_DEBUG ((LM_DEBUG,
//                           "**** LOAD == %f\n",
//                           load.value));

              if (i > 0 && load.value != 0)
                {
                  /*
                    percent difference =
                      (min_load - load.value) / load.value
                      == (min_load / load.value) - 1

                      The latter form is used to avoid a potential
                      arithmetic overflow problem, such as when
                      (min_load - load.value) > FLT_MAX, assuming that
                      either load.value is negative and min_load is
                      positive, or vice versa.
                  */
                  const CORBA::Float percent_diff =
                    (min_load / load.value) - 1;

                  /*
                    A "thundering herd" phenomenon may occur when
                    location loads are basically the same (e.g. only
                    differ by a very small amount), where one object
                    group member ends up receiving the majority of
                    requests from different clients.  In order to
                    prevent a single object group member from
                    receiving such request bursts, one of two equally
                    loaded locations is chosen at random.  Thanks to
                    Carlos, Marina and Jody at ATD for coming up with
                    this solution to this form of the thundering herd
                    problem.

                    See the documentation for
                    TAO_LB::LL_DEFAULT_LOAD_PERCENT_DIFF_CUTOFF in
                    LB_LeastLoaded.h for additional information.
                  */
                  if (percent_diff <= TAO_LB::LL_DEFAULT_LOAD_PERCENT_DIFF_CUTOFF)
                    {
                      // Prevent integer arithmetic overflow.
                      const CORBA::Float NUM_MEMBERS = 2;

                      // n == 0:  Use previously selected location.
                      // n == 1:  Use current location.
                      const CORBA::ULong n =
                        ACE_static_cast (CORBA::ULong,
                                         NUM_MEMBERS * ACE_OS::rand ()
                                         / (RAND_MAX + 1.0));

                      ACE_ASSERT (n == 0 || n == 1);

                      if (n == 1)
                        {
                          min_load = load.value;
                          location_index = i;
                          found_location = 1;

//                           ACE_DEBUG ((LM_DEBUG,
//                                       "** NEW MIN_LOAD == %f\n",
//                                       min_load));
                        }

//                       if (n == 0)
//                         ACE_DEBUG ((LM_DEBUG, "^^^^^ PREVIOUS LOCATION\n"));
//                       else
//                         ACE_DEBUG ((LM_DEBUG, "^^^^^ CURRENT LOCATION\n"));

                    }
                  else
                    {
                      min_load = load.value;
                      location_index = i;
                      found_location = 1;

//                       ACE_DEBUG ((LM_DEBUG,
//                                   "***** NEW MIN_LOAD == %f\n",
//                                   min_load));
                    }
                }
              else
                {
                  min_load = load.value;
                  location_index = i;
                  found_location = 1;

//                   ACE_DEBUG ((LM_DEBUG,
//                               "NEW MIN_LOAD == %f\n",
//                               min_load));
                }
            }

          // ACE_DEBUG ((LM_DEBUG, "NEW MIN_LOAD == %f\n", min_load));
        }
      ACE_CATCH (CosLoadBalancing::LocationNotFound, ex)
        {
          // No load available for the requested location.  Try the
          // next location.
        }
      ACE_ENDTRY;
      ACE_CHECK_RETURN (0);
    }

//   ACE_DEBUG ((LM_DEBUG,
//               "FOUND_LOAD     == %u\n"
//               "FOUND_LOCATION == %u\n",
//               found_load,
//               found_location));

  // If no loads were found, return without an exception to allow this
  // strategy to select a member using an alternative method
  // (e.g. random selection).
  if (found_load)
    {
      if (found_location)
        location = locations[location_index];
      else if (this->reject_threshold_ != 0)
        ACE_THROW_RETURN (CORBA::TRANSIENT (), 0);

//       ACE_DEBUG ((LM_DEBUG, "LOCATION ID == %s\n", location[0].id.in ()));
    }

//   ACE_DEBUG ((LM_DEBUG, "LOCATED = %u\n", location_index));

  return found_location;
}

void
TAO_LB_LeastLoaded::init (const PortableGroup::Properties & props
                          ACE_ENV_ARG_DECL)
{
  CORBA::Float critical_threshold =
    TAO_LB::LL_DEFAULT_CRITICAL_THRESHOLD;
  CORBA::Float reject_threshold = TAO_LB::LL_DEFAULT_REJECT_THRESHOLD;
  CORBA::Float tolerance = TAO_LB::LL_DEFAULT_TOLERANCE;
  CORBA::Float dampening = TAO_LB::LL_DEFAULT_DAMPENING;
  CORBA::Float per_balance_load = TAO_LB::LL_DEFAULT_PER_BALANCE_LOAD;

  const PortableGroup::Property * ct = 0;  // critical threshold property
  const PortableGroup::Property * rt = 0;  // reject   threshold property

  const CORBA::ULong len = props.length ();
  for (CORBA::ULong i = 0; i < len; ++i)
    {
      const PortableGroup::Property & property = props[i];
      if (ACE_OS::strcmp (property.nam[0].id.in (),
                          "org.omg.CosLoadBalancing.Strategy.LeastLoaded.CriticalThreshold") == 0)
        {
          this->extract_float_property (property,
                                        critical_threshold
                                        ACE_ENV_ARG_PARAMETER);
          ACE_CHECK;

          ct = &property;
        }

      else if (ACE_OS::strcmp (property.nam[0].id.in (),
                               "org.omg.CosLoadBalancing.Strategy.LeastLoaded.RejectThreshold") == 0)
        {
          this->extract_float_property (property,
                                        reject_threshold
                                        ACE_ENV_ARG_PARAMETER);
          ACE_CHECK;

          rt = &property;
        }

      else if (ACE_OS::strcmp (property.nam[0].id.in (),
                               "org.omg.CosLoadBalancing.Strategy.LeastLoaded.Tolerance") == 0)
        {
          this->extract_float_property (property,
                                        tolerance
                                        ACE_ENV_ARG_PARAMETER);
          ACE_CHECK;

          // Valid tolerance values are greater than or equal to one.
          if (tolerance < 1)
            ACE_THROW (PortableGroup::InvalidProperty (property.nam,
                                                       property.val));
        }

      else if (ACE_OS::strcmp (property.nam[0].id.in (),
                               "org.omg.CosLoadBalancing.Strategy.LeastLoaded.Dampening") == 0)
        {
          this->extract_float_property (property,
                                        dampening
                                        ACE_ENV_ARG_PARAMETER);
          ACE_CHECK;

          // Dampening range is [0,1).
          if (dampening < 0 || dampening >= 1)
            ACE_THROW (PortableGroup::InvalidProperty (property.nam,
                                                       property.val));
        }

      else if (ACE_OS::strcmp (property.nam[0].id.in (),
                               "org.omg.CosLoadBalancing.Strategy.LeastLoaded.PerBalanceLoad") == 0)
        {
          this->extract_float_property (property,
                                        per_balance_load
                                        ACE_ENV_ARG_PARAMETER);
          ACE_CHECK;
        }
    }

  if (critical_threshold != 0 && reject_threshold != 0
      && critical_threshold <= reject_threshold)
    ACE_THROW (PortableGroup::InvalidProperty (ct->nam, ct->val));

  this->properties_ = props;

  this->critical_threshold_ = critical_threshold;
  this->reject_threshold_   = reject_threshold;
  this->tolerance_          = tolerance;
  this->dampening_          = dampening;
  this->per_balance_load_   = per_balance_load;

//   ACE_DEBUG ((LM_DEBUG,
//               "--------------------------------\n"
//               "critical_threshold = %f\n"
//               "reject_threshold   = %f\n"
//               "tolerance          = %f\n"
//               "dampening          = %f\n"
//               "per_balance_load   = %f\n"
//               "--------------------------------\n",
//               critical_threshold,
//               reject_threshold,
//               tolerance,
//               dampening,
//               per_balance_load));
}

void
TAO_LB_LeastLoaded::extract_float_property (
  const PortableGroup::Property & property,
  CORBA::Float & value
  ACE_ENV_ARG_DECL)
{
  if (!(property.val >>= value))
    ACE_THROW (PortableGroup::InvalidProperty (property.nam,
                                               property.val));
}