system command in parfor loop

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Sujatha
Sujatha on 17 Jan 2022
Commented: Walter Roberson on 26 Jan 2022
I am invoking a C++ executable from the Matlab command prompt.
Interactively, it goes like this:
>> [status,cmdout] = system('multi.exe','-echo')
Input unique file identifier. Ex: 2~04-13-013939 - 2~11-30-091444
And this works fine.
However, I need to invoke the C++ executable multiple times. So I created a parfor loop, like so:
parpool
tic
parfor i=1:nfiles
[status,cmdout] = system('multi.exe','-echo')
str3{i,1}
end
where str3 is a series of inputs:
str3 =
14×1 cell array
{'1~11-24-054646'}
{'1~11-24-095017'}
{'1~11-29-060908'}
{'1~11-29-101743'}
{'1~11-30-091225'}
{'2~11-24-055554'}
{'2~11-24-100903'}
{'2~11-29-060541'}
{'2~11-29-101814'}
{'2~11-30-091444'}
{'3~11-24-055933'}
{'3~11-29-101847'}
{'4~11-24-060505'}
{'4~11-29-101935'}
This ran for over 54 hours, but the task never completed, and I eventually hit Ctrl-C.
Any thoughts/ feedback?
  2 Comments
jessupj
jessupj on 17 Jan 2022
just to play devil's advocate, i've approached a similar problem in the past by calling parallel instances of matlab from the shell. it was by no means the most I/O-efficient method and wasted a lot of time opening and closing matlab & pooling. the individual system jobs were geophysical models that took O(days) so the data importing and pool opening overhead was comparatively insignificant.

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Answers (1)

Walter Roberson
Walter Roberson on 17 Jan 2022
parpool
tic
parfor i=1:nfiles
cmd = sprintf('echo "%s" | multi.exe', str3{i,1});
[status,cmdout] = system(cmd, '-echo')
end
  12 Comments
Walter Roberson
Walter Roberson on 26 Jan 2022
parpool
tic
parfor i=1:nfiles
tname{i} = tempname();
[fid, msg] = fopen(tname{i});
if fid < 0
error('iteration %d failed to create temporary file "%s" because "%s"', i, tname{i}, msg);
end
fprintf(fid, '%s\n\n', str3{i,1});
fclose(fid)
cmd = sprintf('multi.exe < "%s"', tname{i});
[status,cmdout] = system(cmd, '-echo')
end

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