Run move and collect functions in parallel

I have a translation stage that I want to move over a set of positions. While the stage is moving I want to record data collected from an oscilliscope. The data is collected in a function using a while loop that periodically queries the buffer of the oscilliscope. The timing of the data read and stage movement are NOT synced. So I would like to continously collect data while the stage is moving and then stop once the stage finishes its motion. How can I do this using parpool and parfeval.

Conceptual code follows

parpool('Processes',1)

points = linspace(1,10,100);  %positions to move translation stage
movePos(points)  %move the stage to each point
parfeval(@getData,0,D) %read data from the oscilliscope while stage is moving

function data = getData(opts)  %get data from the oscilliscope
    data = [];
    while isStageMoving  %collect data while the stage is moving
        datatemp = readOscope; %read segment of data
        data = [data datatemp]; %concatonate data as it is collected
    end
end

function movePos(points)  %move the translation stage
    isStageMoving = 1; 
    send(D,isStageMoving) %send to getData function to start data collection
    nPoints = length(points) %loop over the positions that I want to move stage
    for iPoints = 1:nPoints
        movestage(points(iPoints))
    end
    isStageMoving = 0;
    send(D,isStageMoving) %send to getData function to stop data collection
end

Answer 1

[Raymond Norris]

@Christopher Saltonstall here's an approach using spmd with two workers.

% function saltonstall

% 1. How is "D/opts" assigned and used?
% 2. What are we doing with "data" in getData()?
% 3. Does movePos need to return anything or does movestage do everything?
% 4. Can we block MATLAB while this spmd block is running or should it be
%    non-blocking (this could be done)?

parpool("Threads",2);

spmd
    if spmdIndex==1
        % Move the translation stage
        
        % Kick start reading Oscope on worker 2
        spmdSend("start",2)
        
        points = linspace(1,10,100);
        nPoints = length(points);
        for iPoints = 1:nPoints
            movestage(points(iPoints))
        end
        
        % Signal worker 2 to stop reading Oscope
        spmdSend("stop",2)
        
    elseif spmdIndex==2
        % Get data from the oscilliscope
        
        % Get the signal from worker 1 to start
        spmdReceive(1);
        
        data = [];
        while true
            % Get data from the oscilliscope
            datatemp = readOscope();
            data = [data datatemp]; %#ok<AGROW>
            
            if spmdProbe
                % Got a signal, should we stop?
                cmd = spmdReceive(1);
                if strcmp(cmd,"stop")
                    break
                end
            end
        end
    end
end

% Pull the data from worker 2 and plot it
ldata = data{2};
plot(ldata)

[Christopher Saltonstall]

This is great thank you. I updated it to run and test that it works without hardware.

What is the spmdProbe? That seem useful for adding an abort. This is going into a GUI. It would be nice to have an abort button to stop the measurements if there is an issue.

clear
close all

poolobj = gcp('nocreate');
if isempty(poolobj)
poolobj = parpool('Threads',2);
else 
    poolsize = poolobj.NumWorkers
end
D = parallel.pool.DataQueue;

spmd
    if spmdIndex==1
        % Move the translation stage
        
        % Kick start reading Oscope on worker 2
        spmdSend("start",2)
        
        points = linspace(1,10,100);
        nPoints = length(points);
        for iPoints = 1:nPoints
            %movestage(points(iPoints))
            disp(['Point ' num2str(iPoints) ': ' num2str(points(iPoints))])
            pause(0.25)
        end
        
        % Signal worker 2 to stop reading Oscope
        spmdSend("stop",2)
        
    elseif spmdIndex==2
        % Get data from the oscilliscope
        
        % Get the signal from worker 1 to start
        spmdReceive(1);
        
        data = [];
        while true
            % Get data from the oscilliscope
            t = -pi:0.01:pi;
            datatemp = rand(1)*sin(t + rand(1)*pi);
            data = [data datatemp]; 
            pause(0.03)
            if spmdProbe
                % Got a signal, should we stop?
                cmd = spmdReceive(1);
                if strcmp(cmd,"stop")
                    break
                end
            end
        end
    end
end
% Pull the data from worker 2 and plot it
ldata = data{2};
plot(ldata)

[Raymond Norris]

@Christopher Saltonstall if the workers need to send data back to the MATLAB client to update a UI in "real time", I would suggest you look at Receive Communication on Workers -- it's a good working example of what you probably want. A couple of comments:

• The example is running the same function on each worker. Instead of running a for-loop to spawn the same future on each worker, call parfeval twice, each with a different function to run on the worker (i.e., translation and oscope).
• The client is responsible for kicking things off and stopping. Worker 1 is not instructing Worker 2 to do something (if that's what you want). If you have the R2025a prerelease, you can read about pollable dataqueues between workers (where Worker 1 could instruct Worker 2 to do something).