Graphics argument validation for function in parfor loop

I have a function that I'd like to run serially but also sometimes inside a parfor loop, with the ability to optionally plot output. Understandably, I can't plot or modify graphics within a parpool thread, but I find even having unused relevant argument validation that draws from matlab.graphics.axis.Axes class properties causes a parallel:threadpool:NonConcurrentLibrary error to be thrown during parallel execution. Attached is a code snippet demonstrating what I mean.

I suppose I have two questions. First, is this expected behaviour, given that args is not even invoked in the body of the function? Second, is there any way to retain automatic argument validation for an axis object that plays nicely with parfor, in cases where these arguments are used conditionally and never during parallel execution?

function ArgValidationParForTest()
pool = gcp();
fprintf('Parallel pool initialised with %d workers\n', pool.NumWorkers)
ntests = 10;
parfor i = 1:ntests
    TestFunc()
end
end

function TestFunc(args)
arguments
    args.?matlab.graphics.axis.Axes
end
fprintf('Called\n')
end

Answer 1

[Catalytic]

If you use a process-based pool, it will work --

parpool('Processes')

Answer 2

[Matt J]

Second, is there any way to retain automatic argument validation for an axis object that plays nicely with parfor, in cases where these arguments are used conditionally and never during parallel execution?

You would probably have to hand off to a separate validation routine,

function TestFunc(varargin)
  fprintf('Called\n')

  args=handOff(varargin{:});

end


function args=handOff(varargin)
  p = gcp('nocreate');
  args=[];
  if isempty(p) || ~isa(p,'parallel.ThreadPool')
      args=validateGraphics(varargin{:});
  elseif ~isempty(varargin)
      error 'Handle graphics aren''t supported in threadpools'
  end
end


function args=validateGraphics(args)
    arguments
        args.?matlab.graphics.axis.Axes
    end

end