How could I run a while loop asynchronously and break it from a callback function receiving client input? Are there better alternatives?

I am currently using a client/server application where the MATLAB code acts as the server.

The server is meant to execute functions of a device connected to the computer that holds the server application.

Through an ethernet connection, the server receives integers from the python-based client application. The integers are interpreted as instructions for different functions of the device to be executed at the moment they are received. I placed a switch inside the callback function for the server to handle the functions assigned to each integer. The functions of the device run asynchronously.

The program has the following framework.

%Define device object.

%Define parameters for device function.

%Define tcp/ip server

function callbackClientConnection

%If client disconnects

- Clear device object

- Clear TCP/ICP server

function readClientData

%Read Client Data (integer)

swtich

case 0 : Don't do anything

case 1: Eval start device function in base workspace

case 2: Eval stop device function in base workspace

case 3: Eval change parameters of function in base workspace

Previously I only needed to execute the device function once when the server received number 1. This function would last for 4 seconds, and if number 2 was received within that time frame the device's function to stop previous function could be run with no issues, since these functions run asynchronously.

Currently, when I receive number 1 from the client, I need to execute a loop that runs the device's function several times, with a pause between each repetition. This time instead of using the stop device function, I would need for the loop to be broken either by a limit of number of repetetions or ideally by a boolean that changes to false once the server receives number 2 from the client. I've tried setting the while loop in a separate function in the script, and using a global boolean variable that changes to true when 1 is received and changes to false when 2 is received. However this did not work because the server won't read data from the client until the loop finishes running. I also tried using parpool and parfeval, but this did not work either.

The framework I'm trying to use looks like this:

.....

function readClientData

global continueLoop

%Read Client Data (integer)

swtich

case 0 : Don't do anything

case 1: continueLoop = true

deviceFunctionLoop()

case 2: continueLoop = false

case 3: Eval change parameters of function in base workspace

function deviceLoop

global continueLoop

numReps = 4;

i = 1;

while i < numReps & continueLoop

Eval start device function in base workspace

pause(0.250)

i = i +1;

end

Any ideas on how to be able to run this loop asynchronously and be able to break it when receiving number 2 from client?

Answer 1

[Chetan]

Hi @Eugenio Forbes,

It seems like you want to run a loop to check for client commands, executing the loop asynchronously while being able to interrupt it based on client commands.

To address this issue, consider using MATLAB's `timer` objects.

A `timer` object can be set up to execute its callback function at specified intervals, allowing your server to periodically check for new client commands without blocking the main thread that listens for incoming data.

1. Define a `timer` object for running the device function loop. This allows the main server thread to remain responsive to incoming client commands.
2. Use the `timer` callback to execute the device function. Within this callback, check the global `continueLoop` variable to determine if the loop should continue or be stopped.
3. Adjust the `timer` execution based on client commands. When a start command (1) is received, start or resume the timer. When a stop command (2) is received, stop the timer, effectively breaking the loop.

Here's a simplified example to illustrate this approach:

% Define global variable
global continueLoop;

% Define the timer object globally or in an appropriate scope
global deviceTimer;
deviceTimer = timer('ExecutionMode', 'fixedSpacing', ...
    'Period', 0.250, ... % Adjust the period to match your device function's requirements
    'TimerFcn', @deviceFunctionLoop);

function readClientData
global continueLoop;
global deviceTimer;
% Read Client Data (integer)
switch
    case 0
        % Don't do anything
    case 1
        continueLoop = true;
        if strcmp(deviceTimer.Running, 'off')
            start(deviceTimer);
        end
    case 2
        continueLoop = false;
        stop(deviceTimer); % This will allow the loop to be interrupted
    case 3
        % Eval change parameters of function in base workspace
end
end

function deviceFunctionLoop(~, ~)
global continueLoop;
if ~continueLoop
    % Optionally, stop the timer here if you want to ensure it doesn't fire again
    stop(deviceTimer);
    return;
end
% Eval start device function in base workspace
end

Refer to the following MathWorks Documentation for more details:

https://www.mathworks.com/help/matlab/ref/timer.html

Thanks,

Chetan