(par)for k=1:N end; select for or parfor loop without code replication
显示 更早的评论
I like to use for-loop or parfor-loop with function input flag. One way to do that is using if-else with code replication. I wonder is there a cleverer way?
% solution based on code replication
function foo(parflag)
if parflg==true
parfor k=1:3
% processing codes
end
else
for k=1:3
% copy of processing codes
end
end
end
%% wondering how to make this idea work?
function hoo(parflag)
if parflag==true
forString = str2func('parfor')
else
forString = str2func('for')
end
forString k=1:3
% processing codes
end
end
采纳的回答
You can avoid replicating the loop code as follows.
numWorkers={}; % or whatever
if ~parflag
numWorkers={0};
end
parfor (k=1:3, numWorkers{:})
% processing codes
end
Be mindful, though, that parfor loops have stronger requirements on the code structure, and you would be limiting yourself to that, even when running serially.
13 个评论
Bruno Luong
2023-8-23
编辑：Bruno Luong
2023-8-23
does it start the parallel pool, etc... even for simple for-loop?
Matt J
2023-8-23
No, it doesn't.
Simon
2023-8-23
Parfor with zero worket would be a bit slower than for loop
Bruno Luong
2023-8-23
Same question for to parfeval? Can I set something for mypool so that it runs without parallel pool?
mypool = backgroundPool;
Future(1) = parfeval(mypool,@(x)sin(x), 1, pi);
% ...
Matt J
2023-8-23
Same question for to parfeval
That I don't know, but it's less of a problem, because parfeval has a functional form, unlike parfor. You could therefore make a wrapper for parfeval that will handle the pool-free case.
Sam Marshalik
2023-8-23
To add on to Matt's great comments, you can pass an empty pool flag to parfeval and it will run in serial in the background. Here is an example of what I mean:
delete(gcp); % Ensure no pool is open
p = gcp('nocreate');
% No pool exists, so p is empty
for i = 1:3
f(i) = parfeval(p,@pause, 0);
end
p = parpool("Threads");
% p exists and will be used to run parfeval
for i = 1:3
f(i) = parfeval(p,@pause, 0);
end
In short, you can pass the pool object over to parfeval and if it is empty, it won't be used.
Bruno Luong
2023-8-23
编辑：Bruno Luong
2023-8-23
@Sam Marshalik great thank you !
I just tested it in my real project and it seems working well. Now I have one base code for both parallel and non-parallel calculation.
This is also a convenient way to debug the parallel code, just switch to empty pool and voilà.
Simon
2023-8-24
Bruno Luong
2023-8-24
编辑：Bruno Luong
2023-8-24
Good question, further more passing cell is not documented as from parfor doc
"parfor (loopvar = initval:endval, M); statements; end executes statements in a loop using a maximum of M workers or threads, where M is a nonnegative integer."
Bruno Luong
2023-8-24
But then you have to manually set numWorkers
Simon
2023-8-24
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