Communicate with worker through client

Question

guy sharon 2019-9-22

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/481584-communicate-with-worker-through-client

评论： guy sharon 2019-9-25

Hello!

I have an app (app designer/GUIDE) which calls a function that looks something like this

function func()
    spmd
        switch labindex
            case 1
                while (true)
                    % some code...
                end
            case 2
                while (true)
                    % some code...
                end
        end
    end
end

and I would like to be able to break out of the while loop for each workers of the spmd with a click of a button in the app, which means I have to send data from the client to the workers.

I know I can easily send data from the workers to the client, but I'm not sure about the reverse direction.

Please help, thanks!

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Answer 1

Edric Ellis 2019-9-23

1
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https://ww2.mathworks.cn/matlabcentral/answers/481584-communicate-with-worker-through-client#answer_393061

I think it would be better to use parfeval or parfevalOnAll to do this. This way, you can simply cancel the future object returned from those calls to stop the worker execution. You could couple this with a parallel.pool.DataQueue to get the results back from the workers. Here's a simple example:

% Build a really simple "UI" - just a histogram and a button
pool = gcp();
fig  = uifigure();
grid = uigridlayout(fig, [1, 2]);
ax   = axes(uipanel(grid));
btn  = uibutton(grid);
hist = histogram(ax, 'BinEdges', 0.5 + (0:pool.NumWorkers));
% Set up a DataQueue to let the workers send results back to the client
Q = parallel.pool.DataQueue();
% Each time a worker sends a piece of data to the client, append it
% to the histogram
listener = afterEach(Q, @(data) appendData(hist, data));
% Trigger the work on the workers, hook up the future to the button
% so that pressing the button cancels 'fut'.
fut = parfevalOnAll(@doWork, 0, Q);
btn.ButtonPushedFcn = @(~,~) cancel(fut);
%% function to do work on the workers
function doWork(Q)
task = getCurrentTask;
myId = task.ID;
while true
    send(Q, myId);
    pause(myId/4);
end
end
%% function to append data to the histogram
function appendData(hist, data)
hist.Data(end+1) = data;
end

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Edric Ellis 2019-9-25

labSend and labReceive can only be used inside spmd. Unfortunately, spmd is a synchronous construct on the client, so there's no way for the client to interrupt the workers.

guy sharon 2019-9-25