GetGlobal() and parfor loop

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Hello everyone,

I am using the setGlobal() and getGlobal() functions in a code that worked pretty well initially but doesn't work now that I'm trying to parrallelize it.

I noticed that the functions setGlobal() and getGlobal() struggle to work with the parfor loop. or example, when I run

setGlobalF([2 3 4])
% j = getGlobalF();
parfor i = 1:4
    j = getGlobalF()
end

the j value is not assigned to [2 3 4].

Have you guys any ideas of why and how should I proceed ? Thanks !

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Quentin Reynard-Feytis 2022-7-13

在 MATLAB Online 中打开

I forget to put the function, here it is

function r = getGlobalF
global F
r = F;
end
function setGlobalF(val)
global F
F = val;
end

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Answer 1

Walter Roberson 2022-7-13

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Global and persistent variables are never copied to workers.

You need to do one of two things:

run the setGlobalF command on each worker, such as using parfevalOnAll
use parallel.pool.Constant to push a constant value into the workers, that you can then access.

Note that any setGlobalF that you do on a worker will not affect the other workers. If you need to be able to affect the other workers, then you should either use spmd with labSend and labReceive or else use parallel.pool.DataQueue or parallel.pool.PollableDataQueue to send data from the workers to the client and then the client would send the updated values to the other workers.

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Quentin Reynard-Feytis 2022-7-13

Thank you very much for your answer you made everything way much clearer :)

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GetGlobal() and parfor loop

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