Vicon DataStream MATLAB SDK

I am working with Vicon Nexus DataStream SDK in MATLAB and I am looking to sample two streams simultaneously. The two streams are from two separate force plates (ForcePlateCount, below). I realize that the index for each forceplate (1 & 2 respectively) will execute the loop as 1 or 2 in each iteration. The code listed below is all nested in a large while loop. Does anyone have experience running this with the parallel computing toolbox (i.e. using a 'parfor' loop on the line 8)? Would this be an appropriate application of the parallel computing toolbox?

Thank you!

while ishandle( MessageBox )
...

% Count the number of force plates
  ForcePlateCount = MyClient.GetForcePlateCount().ForcePlateCount;
  % This will equal 2 in the current setup

    for ForcePlateIndex = 1:ForcePlateCount
        ...        
        % Get the number of subsamples associated with this device.
        Output_GetForcePlateSubsamples = MyClient.GetForcePlateSubsamples( ForcePlateIndex );

        ...
        for ForcePlateSubsample = 1:Output_GetForcePlateSubsamples.ForcePlateSubsamples
            % Output all the subsamples.
            fprintf( '      Sample #%d:\n', ForcePlateSubsample - 1 );

            Output_GetGlobalForceVector = MyClient.GetGlobalForceVector( ForcePlateIndex, ForcePlateSubsample );
            fprintf( '      Force (%g, %g, %g)\n',                           ...
                Output_GetGlobalForceVector.ForceVector( 1 ), ...
                Output_GetGlobalForceVector.ForceVector( 2 ), ...
                Output_GetGlobalForceVector.ForceVector( 3 ) );

            Output_GetGlobalMomentVector = MyClient.GetGlobalMomentVector( ForcePlateIndex, ForcePlateSubsample );
            fprintf( '      Moment (%g, %g, %g)\n',                            ...
                Output_GetGlobalMomentVector.MomentVector( 1 ), ...
                Output_GetGlobalMomentVector.MomentVector( 2 ), ...
                Output_GetGlobalMomentVector.MomentVector( 3 ) );

            Output_GetGlobalCentreOfPressure = MyClient.GetGlobalCentreOfPressure( ForcePlateIndex, ForcePlateSubsample );
            fprintf( '      CoP (%g, %g, %g)\n',                                       ...
                Output_GetGlobalCentreOfPressure.CentreOfPressure( 1 ), ...
                Output_GetGlobalCentreOfPressure.CentreOfPressure( 2 ), ...
                Output_GetGlobalCentreOfPressure.CentreOfPressure( 3 ) );
        end% ForcePlateSubsample
    end% ForcePlateIndex
...
end

[Walter Roberson]

This appears to refer to https://www.vicon.com/products/software/datastream-sdk

Answer 1

[Walter Roberson]

It is common that access from different workers is not possible in the case where the data is coming from a single hardware device, even if that hardware device is handling multiple channels. Device drivers often lock access down to one process at a time as doing so means that they do not have to keep state for each distinct connection. parfor workers are different processes.

But sometimes it is possible, especially if the connection is made by way of ActiveX. In such a case the trick is that the MyClient needs to be recreated on each worker. Typically the easiest way to do that is to run the initialization code on each worker by using parfevalOnAll()