Ownership Transfer will break Latency Compensation

[Dan Dexter]

Ownership transfer of object attributes can break latency compensation because the data flow between sim-data and lag-comp data will be broken.

This example will illustrate the issue.

1. Federate-1 is configured to publish and subscribe all attributes of an object names Test.
2. Federate-1 is configured to create the Test object instance (i.e. owns the privilege to delete).
3. Federate-1 is configured to do send-side lag-compensation. It is wired to compensate sim-data and the output is the lag-comp data state.
4. When ownership of the Test attributes are transferred to another federate, Federate-1 will now be receiving Test data reflections.
5. Because Federate-1 was configured for send-side lag-compensation the receive-side lag-compensation API is not called, resulting in the reflected Test data received on the lag-comp data variables not being transferred to the sim-data. The return data flow is broken.

Need an API to detect the ownership transfer and bypass lag-compensation so that data still goes in or out of the federate.

The ability to bypass lag-compensation should also allow a user to disable lag-compensation at runtime without having to change the simulation or the input file configuration for the object attributes.

[Dan Dexter]

The LagCompensation API has been updated to add two functions the user must implement to bypass both send and receive side lag-compensation. This will also allow lag-compensation to be disabled at runtime in the input file without having to change the S_define file.

/*! @brief When lag compensation is disabled, this function is called to
 * bypass the send side lag compensation and your implementation must copy
 * the sim-data to the lag-comp data to effect the bypass. */
virtual void bypass_send_lag_compensation() = 0;

/*! @brief When lag compensation is disabled, this function is called to
 * bypass the receive side lag compensation and your implementation must
 * copy the lag-comp data to the sim-data to effect the bypass. You must
 * make sure to check the lag-comp data was received before copying to
 * the sim-data otherwise you will be copying stale data. */
virtual void bypass_receive_lag_compensation() = 0;

From the SIM_sine/RUN_a_side/input.py file, to disable lag-compensation, set the lag_comp_type to trick.LAG_COMPENSATION_NONE without having to change the lag_comp callback setting.

THLA.manager.objects[0].lag_comp      = A.lag_compensation
THLA.manager.objects[0].lag_comp_type = trick.LAG_COMPENSATION_NONE

From the SineLagCompensation.cpp file showing example bypass functions to ensure data continues to flow even when lag-compensation is bypassed in the event of it being disabled or ownership transfer:

void SineLagCompensation::bypass_send_lag_compensation()
{
   // Bypass send lag compensation by copying the current sim-data to the
   // lag-comp data structure. We need to ensure the lac-comp data structure
   // is updated to ensure any downstream calculations still get data.
   this->set_name( sim_data->get_name() );
   this->set_time( sim_data->get_time() );
   this->set_value( sim_data->get_value() );
   this->set_derivative( sim_data->get_derivative() );
   this->set_phase( sim_data->get_phase() );
   this->set_frequency( sim_data->get_frequency() );
   this->set_amplitude( sim_data->get_amplitude() );
   this->set_tolerance( sim_data->get_tolerance() );
}

void SineLagCompensation::bypass_receive_lag_compensation()
{
   // If the HLA time attribute has changed and is remotely owned (i.e. is
   // coming from another federate) then override our simulation state with the
   // incoming value. If we locally own the attribute then we do not want to
   // override it's value. If we did not do this check then we would be
   // overriding state of something we own and publish with whatever value
   // happen to be in the local variable, which would cause data corruption of
   // the state. We always need to do this check because ownership transfers
   // could happen at any time or the data could be at a different rate.
   // Because of ownership transfers and attributes being sent at different
   // rates we need to check to see if we received data for each attribute.

   // Bypass receive lag compensation by copying lag-comp data to sim-data.
   if ( name_attr->is_received() ) {
      sim_data->set_name( this->get_name() );
   }
   if ( time_attr->is_received() ) {
      sim_data->set_time( this->get_time() );
   }
   if ( value_attr->is_received() ) {
      sim_data->set_value( this->get_value() );
   }
   if ( dvdt_attr->is_received() ) {
      sim_data->set_derivative( this->get_derivative() );
   }
   if ( phase_attr->is_received() ) {
      sim_data->set_phase( this->get_phase() );
   }
   if ( freq_attr->is_received() ) {
      sim_data->set_frequency( this->get_frequency() );
   }
   if ( amp_attr->is_received() ) {
      sim_data->set_amplitude( this->get_amplitude() );
   }
   if ( tol_attr->is_received() ) {
      sim_data->set_tolerance( this->get_tolerance() );
   }
}