Parallel pool constant with a parfor and for loop

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Maria 2021-10-14

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https://ww2.mathworks.cn/matlabcentral/answers/1563626-parallel-pool-constant-with-a-parfor-and-for-loop

评论： Maria 2021-10-15

采纳的回答： Edric Ellis

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Hi,

as far as I understood the usage of parallel pool constants, it really helps when a parfor loop is called several times, like in the example provided in the Help

data = rand(1000);
c = parallel.pool.Constant(data);
for ii = 1:10
    % Run multiple PARFOR loops accessing the data.
    parfor jj = 1:10
        x(ii,jj) = c.Value(ii,jj);
    end
end

However, what if I have the opposite, meaning, I have an external parfor, and the inner loop is a for loop. For example, I have something like this

parfor m = 1 : M
    for n = 1 : N
        matrix(m,n) = w1(n);
    end
end

Matlab complains that w1 is a broadcast variable.

Would it make sense if I would convert w1 to a parallel.pool.Constant?

采纳的回答

Edric Ellis 2021-10-15

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https://ww2.mathworks.cn/matlabcentral/answers/1563626-parallel-pool-constant-with-a-parfor-and-for-loop#answer_809176

Yes, parallel.pool.Constant is generally most useful when there are multiple parfor loops. (There are other use-cases such as when you need to construct some data directly on the workers)

In your specific case, if you have only a single parfor loop as you show, then there is no benefit to using parallel.pool.Constant for w1, and you can safely ignore the code analyzer message.

The function that you evaluate using batch is run on worker 1. If you use the 'Pool' parameter to batch, then parallel language constructs such as parfor run on workers 2:N. So yes - a matrix created by your batch function will be created on worker 1.

Maria 2021-10-15