MATLAB: Dumthe error in parfor

dummyerrorParallel Computing Toolboxparfor

Hi,

While running a parfor loop i am getting the following error:

Caught-error breakpoint was hit in ParallelException>iGetCurrentStack at line 183. The error was:
Error using ParallelException>iGetCurrentStack (line 183)
This is a dummy error
183     error('parallel:internal:cluster:DummyError', 'This is a dummy error')

Does anyone know what this error means?

Best Answer

Hi Laurent,

It looks like you have done

dbstop if all error

or something similar.

That error is used to deduce the current stack and is purely an implementation detail. You don't need to worry about it. I think you'll find more interesting errors further up the stack of your application.

Thanks, Elwin

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MATLAB: -maxNumCompThreads, hyperthreading, and parpool

I was wrong about maxNumCompThreads not working on parpool workers. I think the problem was that the code I was using:

parfor j = 1:2
  tic
      maxNumCompThreads(2);
      workersCompThreads(j) = maxNumCompThreads;
      i = 1;
      while toc < 200
          a = randn(10^i)*randn(10^i);
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used so much memory by the time I checked CPU utilization that the bottleneck was I/O and the extra threads were already shut down. When I did the following:

parfor j = 1:2
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The extra threads started and stayed running.

As for the second issue, I got a confirmation from the Mathworks that the parent Matlab process won't start more threads than the number of physical cores, even if you explicitly raise the limit beyond that. So in the documentation, the sentence:

"Currently, the maximum number of computational threads is equal to the number of computational cores on your machine."

should say:

"Currently, the maximum number of computational threads is equal to the number of physical cores on your machine."

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Try placing a try-catch statement around where the error occurs. Note that try-catch can slow down performance, but I guess it's better than stopping all jobs.

parfor j = 1:NumberOfJobs
  try
    %Do the unpredictable function here
  catch
  end
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Best Answer

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