Nested parfor effecting fprintf?

Question

Ali Almakhmari 2023-8-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2006512-nested-parfor-effecting-fprintf

评论： Ali Almakhmari 2023-8-9

Hey guys. I have a gigantic while loop, and inside of it, I have multiple for loops. One of those for loops is a parfor. Now my questions is this okay? Is there any harm of doing this? I stumbled upon this: https://www.mathworks.com/help/parallel-computing/nested-parfor-loops-and-for-loops.html. And it got me a bit confused.

To be honest, I am a bit worried because my setup is like the following:

counter = 0
while(1)
    for ii=1:5
        %blah blah blah
    end
    
    for iii = 1:1022
        %blah blah blah
    end
    
    parfor(iiii = 1,6)
        %blah blah blah
    end
    
    if(something)
        break
    end
    save("something.mat","SOMETHING")
    counter = counter + 1;
    fprintf("\n %d is done",counter)
end

And the fprintf keeps outputing "1 is done" with each counter iteration. Its as if the counter variable is not incremented. And what is worse is that the the saving of the .mat file is not happening. I can see it not being updated in the directory. Which I am beginning to think that it might be due to something related to the parallel processer. Any thoughts?

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Walter Roberson 2023-8-9

Could you confirm that your intention is to have the iiii loop execute only a single iteration with iiii being 1, and that your intention is that 6 workers are to be allocated to the parfor ? Or did you intend to use parfor iiii = 1:6 instead of 1,6 ?

Ali Almakhmari 2023-8-9

Thank you all for your help, the issue was not with MATLAB but with my functions that were called in the for loop...they were messing with my stuff. I still super appreciate you all replying. Thank you again.

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Answer 1

Bruno Luong 2023-8-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2006512-nested-parfor-effecting-fprintf#answer_1285172

编辑：Bruno Luong 2023-8-9

在 MATLAB Online 中打开

I add this line before the IF test

something = rand() < 0.01
if(something)
    break
end

it works for me, my command window

>> toto
Starting parallel pool (parpool) using the 'Threads' profile ...
Connected to parallel pool with 14 workers.
ans =
     6
 1 is done
ans =
     6
 2 is done
ans =
     6
 3 is done
ans =
     6
     ...