Parallel pool constant with a parfor and for loop

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Maria
Maria 2021-10-14
评论： Maria 2021-10-15
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?

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Edric Ellis
Edric Ellis 2021-10-15
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.
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Edric Ellis
Edric Ellis 2021-10-15
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.

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