I need help regarding parfeval implementation with object handle. I have created an object handle, the member functions of which i want to run as parallel processes.

I have created an object handle like this,

classdef example_class<handle

properties

A

B

end

methods

function h=example_class()

h.A=1;

h.B=1;

end

function multiply_A(h,data)

for m=1:10

h.A=h.A*data;

end

end

function add_B(h,data)

for m=1:10

h.B=h.B+data;

end

end

end

end

I want to run the methods multiply_A and add_B as parallel processes which can modify the properties of the original handle object i.e A and B. For this I am using parfeval as given in the below code,

clc;

clear all;

class1=example_class;

fout(1)=parfeval(@class1.multiply_A,0,2);

fout(2)=parfeval(@class1.add_B,0,5);

We can see that the methods dont have any output. They perform the operation on the handle objects only. But when i am running this code, the properties of the handle object 'class1' are not getting changed. A and B are initialized to 1 and they are still retaining the same value after parfeval ends. Anyone can give any idea, how to solve this so that A and B directly gets updated? It is to be noted that, the member functions should not return any value as that is the requirement of the application which i am working on.

[Jeffrey Clark]

@Sourav Chatterjee, Run function in background - MATLAB parfeval (mathworks.com) only schedules the function to execute, you need to Wait for futures to complete - MATLAB wait (mathworks.com) then look to see if there is a failure int the returned future (your fout). It wouldn't suprise me if you have an error due to the background threads possibly having their own address space.

Answer 1

[Edric Ellis]

The documentation here applies to parfeval as well as parfor in the sense that the object instances on the workers are not connected to the object instances back at the client. Any changes you make on the workers will not be reflected back at the client.

So, you need to do something else instead. One way is to use afterEach to update the handles. I modified your class a little bit to separate computation from update, like this:

classdef example_class<handle
    properties
        A
    end
    methods
        function h=example_class()
            h.A=1;
        end
        function newA = multiply_A(h,data)
            % Returns new value, doesn't modify h
            newA = h.A;
            for m=1:10
                 newA = newA*data;
            end
        end
        function apply_A(h, newA)
            % Simply modifies h
            h.A = newA;
        end
    end
end

Then, call it like this:

h = example_class();
% Call "multiply_A(h,2)" and grab the output
fut = parfeval(@multiply_A, 1, h, 2);
% When "fut" is complete, call "apply_A(h, newA)"
% aeFut is a future that becomes complete when the "apply_A" stage
% has happened
aeFut = afterEach(fut, @(newA) apply_A(h, newA), 0);
wait(aeFut); disp(h)