Parallel pool constant with a parfor and for loop
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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
0 个投票
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.
5 个评论
Maria
2021-10-15
Edric Ellis
2021-10-15
Yes, building a large matrix directly on the workers can be a reason to use parallel.pool.Constant as it allows you to avoid transferring it from the client. So, you might do:
c = parallel.pool.Constant(@() ones(10000)) % calls ones(10000) directly on the worker
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.
Maria
2021-10-15
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