Documentation

Using Objects in parfor-Loops

If you are passing objects into or out of a parfor-loop, the objects must properly facilitate being saved and loaded. For more information, see Save and Load Process.

Handle Classes

You can send handle objects as inputs to the body of a parfor-loop, but any changes made to handle objects on the workers during loop iterations are not automatically propagated back to the client. That is, changes made inside the loop are not automatically reflected after the loop.

To get the changes back to the client after the loop, explicitly assign the modified handle objects to output variables of the parfor-loop. In the following example, maps is a sliced input/output variable:

maps = {containers.Map(),containers.Map(),containers.Map()}; 
parfor ii = 1:numel(maps)
    mymap = maps{ii};   % input slice assigned to local copy
    for jj = 1:1000
        mymap(num2str(jj)) = rand;
    end
    maps{ii} = mymap;   % modified local copy assigned to output slice
end 

Sliced Variables Referencing Function Handles

You cannot directly call a function handle with the loop index as an input argument, because this cannot be distinguished from a sliced input variable. If you need to call a function handle with the loop index variable as an argument, use feval.

For example, suppose you had a for-loop that performs:

B = @sin;
for ii = 1:100
    A(ii) = B(ii);
end

A corresponding parfor-loop does not allow B to reference a function handle. So you can work around the problem with feval:

B = @sin;
parfor ii = 1:100
    A(ii) = feval(B,ii);
end