parfeval() doesn't call function

I am trying to process Data from an UDP Server close to realtime.

For that I wrote this MatLab Code to fill a Buffer with the UDP Datagrams and Process the Data (split the strings, etc.) once the Buffer from my MatLab function is full (myBuffer).

During Processing the data (which takes about 0.9s) I need to go on receiving Data and store them in the (now) emptied Buffer.

I found the parfeval-Function of the "Parallel Computing Toolbox" which might suit my needs as I need my function "ProcessData" to run in the background.

The Problem I encountered is that I can't make it run as the parfeval function doesn't enter my function ProcessData. I tested it with setting a breakpoint in ProcessData() but the program never stops. Did I do anything wrong with the function parameters?

That's what MatLab help says: F = parfeval(p,fcn,numout,in1,in2,...) requests asynchronous execution of the function fcn on a worker contained in the parallel pool p, expecting numout output arguments and supplying as input arguments in1,in2,....

Hope you guys can help me with this problem! Thanks in advance.

function ReadVoltage

    %% Specify a Server (host name or IP address) with Port 8080
    u = udp('192.168.0.164', 8080);  %UDP Object Zuhause
    %u = udp('169.254.38.221', 8080);  %UDP Object Pilotfabrik    

    % Buffer in the enclosing function
    myBuffer = {};  %Initialisierung
    MAXBUFFLEN = 100; %Maximale Anzahl an Eintraegen in Buffer (1 Eintrage = 1 Datagram)

    u.InputBufferSize = 4060; 
    u.ReadAsyncMode = 'continuous';
    u.DatagramReceivedFcn = @DatagramReceivedFcn;
    u.ErrorFcn = @ErrorFcn;
    u.DatagramTerminateMode = 
    u.Terminator = '!';

    %% Initialize Parallel pool 
    pool = gcp();

    %% Oeffnen der Verbindung
    fopen(u);

     if (~strcmp(u.Status,'open'))
         NetworkError(u,'Connection failed!');
     end


    %% Start Data transmission by trigger
    fprintf(u, 'Requesting Data')

    %% Callback Funktion
    function DatagramReceivedFcn(u,~) 

        datagram = fscanf(u);
        disp('Data Received!');


        myBuffer{end+1} = datagram;         %Appends datagram to buffer


        [~, bufflen] = size(myBuffer);

        if bufflen < MAXBUFFLEN
            return;
        else
            f = parfeval(pool, @ProcessData, 1, myBuffer);
            myBuffer = {};               %empty Buffer
        end 

    end

    function ErrorFcn(u,~) 
        disp("An Error occured");
    end

end

function datagram_values = ProcessData(myBuffer)


    stringvalues = split(myBuffer, ";");        %Split Strings
    doublevalues = str2double(stringvalues)     %Convert Strings do Doubles

    dim_doublevalues = size(doublevalues);      %Dimension of Double Output Array

    i_max = dim_doublevalues(2)                 %Anzahl der Datenpakete
    j_max = (dim_doublevalues(3))-1             %Anzahl der Werte pro Datenpaket; -1 wegen leerem Wert nach ";" am Ende
    k_max = i_max*j_max                         %Gesamtanzahl der Werte in Buffer

    k=1;
    while k<=k_max
        for i = 1:i_max
            for j = 1:j_max
                    datagram_values(k,1)=doublevalues(1,i,j);
                    k=k+1;
            end
        end
    end

    disp(datagram_values);


end

Answer 1

[Edric Ellis]

Unfortunately, the MATLAB debugger can't stop in code running on the workers - only code running at the client.

In this case, you should try looking at the diary output of the future f, like this:

f = parfeval(..);
wait(f); % wait for the worker to complete
disp(f.Diary); % display the output

If you don't wish to block the client, you could use afterEach to invoke the call to disp, like this:

f = parfeval(..);
afterEach(f, @(f) disp(f.Diary), 0, 'PassFuture', true);