parfor and handle classes - matlab

Question

I have a handle class:
classdef A<handle
properties
a;
end
methods
function obj = A(a)
obj.a=a;
end
end
end
And I have a cell array of A objects:
arr={};
for i=1:3
arr{i}=A(i);
end
What I would like to do is pass that cell array to a parfor loop so that each object's value will change:
parfor i=1:3
arr{i}.a=i*5;
end
However, this code does not change arr at all. Indeed, here it states that
Changes made to handle classes on the workers during loop iterations are not automatically propagated to the client.
How can I overcome this?

Answer 1

An interesting question; I actually never encountered this problem. It's always good to know everything about parfor limitations, so I did some googlin' and came up with this:
I have received an answer to this issue from technical support.
Apparently the Mathworks regard it as a 'feature' that changes to
objects are not returned - though I can't see that it's a very useful
feature. Anyway, the way to get modified class properties returned
from a parfor loop is to make an explicit change which can be
recognised by parfor. Here are two examples which work for the above
example object:
parfor n = 1:num
exArray(n).data = n:n+5;
end
or
parfor n = 1:num
temp = exArray(n);
setData(temp,n:n+5);
exArray(n) = temp;
end
Actually, if you change any object property it also seems to work. So
for example this also works, if there is a second property data2 which
is set explicitly, both data and data2 are correctly returned:
parfor n = 1:num
setData(exArray(n),n:n+5);
exArray(n).data2 = n:n+5;
end
Where the example object is given by
classdef Example < handle
properties
data
end
methods
function obj = Example(data)
obj.data = data;
end
function setData(obj,data)
obj.data = data;
end
function data = getData(obj)
data = obj.data;
end
end
end
and the array is initialized simply as
% Initialise array of objects
for n = 1:num
exArray(n) = Example(zeros(1,6));
end