Updating Waitbar throws error while using matlabpool

Question

I'm currently working in Matlab and for the first time I'm trying parallel processing. My code works just fine until I add matlabpool('open',4); at the top of my code and matlabpool('close'); at the bottom.

If I add these two lines all of my CPU-Cores are at 100% workload (like it was intended) and my code still works exept the waitbar I implemented inside a parfor-loop.

The code looks ruffly like this:

matlabpool('open',4);

global bar;
bar = waitbar(0, 'Waitbar');


parfor i=1:1000

    //working code

    try
        waitbar(UPDATED_VALUE, bar, UPDATED_STRING);
    end
end

try
    close(bar);
end

//display results


matlabpool('close');

The error I get is the following:

Warning: This functionality is no longer supported under the -nodisplay and -noFigureWindows startup options. For more information, see "Changes to -nodisplay and -noFigureWindows Startup Options" in the MATLAB Release Notes. To view the release note in your system browser, run  web('http://www.mathworks.com/access/helpdesk/help/techdoc/rn/br5ktrh-1.html#br5ktrh-3', '-browser')
In uitools\private\warnfiguredialog at 26
In waitbar at 38
In montecarlo>(parfor body) at 41
In parallel_function>make_general_channel/channel_general at 891
In remoteParallelFunction at 28 

I really don't know what I'm doing wrong. Can someone help me please?

Answer 1

I think the thing you did 'wrong' was to use a waitbar inside a parfor loop haha. But seriously I'm afraid that's because iterations are not executed in order inside a parfor loop so using a regular waitbar is prohibited because of the way information is shared between the Matlab client and the workers executing the loop. Even if you did not write matlabpool('open',4) MATLAB would have opened it so the problem is really the fact that the waitbar is in a parfor loop.

As a workaround you might want to look at this submission form the File Exchange. It was written by Edric Ellis who works at The Mathworks so I would trust his program :)

Hope that helps!