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

[Jake]

Thanks, I think this level of burying removes a lot of the benefits of argument validation for me (CLI completion, code clarity). But, it's nice to know such a solution is possible

[Matt J]

You can recover some of the benefits of CLI by adding an explicit argument list, i.e., by copy-pasting the following auto-generated argument list into your TestFunc arguments block. This block knows only the names of the name/value parameters, and not any of the defaut values and type restrictions. So you would still need to use the handOff function to do the validation proper. However, it at least it will complete the parameter names for you.

disp(char( "  args."+properties("matlab.graphics.axis.Axes") ))

  args.CameraPosition          
  args.CameraPositionMode      
  args.CameraTarget            
  args.CameraTargetMode        
  args.CameraUpVector          
  args.CameraUpVectorMode      
  args.CameraViewAngle         
  args.CameraViewAngleMode     
  args.View                    
  args.Projection              
  args.LabelFontSizeMultiplier 
  args.AmbientLightColor       
  args.DataAspectRatio         
  args.DataAspectRatioMode     
  args.PlotBoxAspectRatio      
  args.PlotBoxAspectRatioMode  
  args.FontName                
  args.FontAngle               
  args.FontWeight              
  args.TickLabelInterpreter    
  args.XLim                    
  args.XLimMode                
  args.YLim                    
  args.YLimMode                
  args.ZLim                    
  args.ZLimMode                
  args.XLimitMethod            
  args.YLimitMethod            
  args.ZLimitMethod            
  args.XDir                    
  args.YDir                    
  args.ZDir                    
  args.CLim                    
  args.CLimMode                
  args.ALim                    
  args.ALimMode                
  args.Layer                   
  args.TickLength              
  args.GridLineWidth           
  args.GridLineWidthMode       
  args.MinorGridLineWidth      
  args.MinorGridLineWidthMode  
  args.GridLineStyle           
  args.MinorGridLineStyle      
  args.XAxisLocation           
  args.XColor                  
  args.XColorMode              
  args.XTick                   
  args.XTickMode               
  args.XTickLabelRotation      
  args.XTickLabelRotationMode  
  args.XLabel                  
  args.XScale                  
  args.XTickLabel              
  args.XTickLabelMode          
  args.XMinorTick              
  args.YAxisLocation           
  args.YColor                  
  args.YColorMode              
  args.YTick                   
  args.YTickMode               
  args.YTickLabelRotation      
  args.YTickLabelRotationMode  
  args.YLabel                  
  args.YScale                  
  args.YTickLabel              
  args.YTickLabelMode          
  args.YMinorTick              
  args.ZColor                  
  args.ZColorMode              
  args.ZTick                   
  args.ZTickMode               
  args.ZTickLabelRotation      
  args.ZTickLabelRotationMode  
  args.ZLabel                  
  args.ZScale                  
  args.ZTickLabel              
  args.ZTickLabelMode          
  args.ZMinorTick              
  args.BoxStyle                
  args.LineWidth               
  args.Color                   
  args.ClippingStyle           
  args.CurrentPoint            
  args.ColorScale              
  args.AlphaScale              
  args.Title                   
  args.TitleHorizontalAlignment
  args.Subtitle                
  args.GridColor               
  args.GridColorMode           
  args.MinorGridColor          
  args.MinorGridColorMode      
  args.GridAlpha               
  args.GridAlphaMode           
  args.MinorGridAlpha          
  args.MinorGridAlphaMode      
  args.XAxis                   
  args.ZAxis                   
  args.Box                     
  args.TickDir                 
  args.TickDirMode             
  args.XGrid                   
  args.XMinorGrid              
  args.YGrid                   
  args.YMinorGrid              
  args.ZGrid                   
  args.ZMinorGrid              
  args.YAxis                   
  args.Units                   
  args.Position                
  args.InnerPosition           
  args.OuterPosition           
  args.PositionConstraint      
  args.TightInset              
  args.Colormap                
  args.Alphamap                
  args.ColorOrder              
  args.ColorOrderIndex         
  args.LineStyleOrder          
  args.LineStyleOrderIndex     
  args.LineStyleCyclingMethod  
  args.FontUnits               
  args.FontSize                
  args.FontSizeMode            
  args.TitleFontWeight         
  args.SubtitleFontWeight      
  args.TitleFontSizeMultiplier 
  args.SortMethod              
  args.Clipping                
  args.NextPlot                
  args.Toolbar                 
  args.Interactions            
  args.InteractionOptions      
  args.ToolbarLocation         
  args.ToolbarLocationMode     
  args.Children                
  args.Parent                  
  args.Visible                 
  args.HandleVisibility        
  args.Layout                  
  args.NextSeriesIndex         
  args.ButtonDownFcn           
  args.ContextMenu             
  args.BusyAction              
  args.BeingDeleted            
  args.Interruptible           
  args.CreateFcn               
  args.DeleteFcn               
  args.Type                    
  args.Tag                     
  args.UserData                
  args.Selected                
  args.SelectionHighlight      
  args.HitTest                 
  args.PickableParts           
  args.Legend