How to block a drawnow from executing callbacks?

Mathworks has recklessly put a drawnow inside of its asynciolib for hardware read and writes:

toolbox\shared\asynciolib\+matlabshared\+asyncio\+internal\Stream.m Line 184: drawnow('limitrate');

This will then execute callbacks in the middle of data transfer! I could remove those lines of code for every Matlab install, but if an update restores the code then I have a dangerous bug. Is there a way I can temporarily pause the event queue from executing callbacks?

The following function CallbackTest has a 10 second main loop which should not be interrupted with the press of a button. However if TCPIP commands are executed in the loop then a hidden drawnow is invoked and the button callback will be processed.

function CallbackTest(Do_TCPIP)

% Test to see if TCPIP reads evaluate callbacks.

% There is a 10s main loop which the button callback should not interrupt.

% The main loop will not be interrupted when Do_TCPIP is 0.

% However when Do_TCPIP is 1 then it will be interrupted.

%Initialize figure and button

hFigure=uifigure();

uibutton(hFigure,ButtonPushedFcn=@ACallBack);

%Initialize TCPIP

echotcpip("on",4000);

t = tcpclient("localhost",4000);

configureTerminator(t,"CR");

waitfor(hFigure,'FigureViewReady')

%10 second main loop which should not be interrupted because there is no drawnow, figure, pause, or waitfor command

n=0;

while n < 20

if Do_TCPIP

writeline(t,"loop");

readline(t);

end

n=n+1;

java.lang.Thread.sleep(500);

end

% Wrap up

echotcpip("off");

delete(hFigure)

fprintf('Done!\n');

end

function ACallBack(~,~)

fprintf('Main loop interrupted.\n');

end

Answer 1

[Nivedita]

Hey Brandon,

You can try using the following approach to block drawnow from executing callbacks:

I have introduced a global flag ALLOW_CALLBACKS to control whether the callback function should proceed with its intended action or simply return without doing anything. This way you can disable the callback during critical sections of the code programmatically. Here is a dummy example code:

function CallbackTest(Do_TCPIP)
    % Initialize control flag
    global ALLOW_CALLBACKS;
    ALLOW_CALLBACKS = true;

    % Initialize the GUI
    hFigure = uifigure('Name', 'Callback Control Test');
    uibutton(hFigure,ButtonPushedFcn=@ACallBack);
    
    % Initialize TCP/IP setup if requested
    if Do_TCPIP
        echotcpip("on", 4000); % Enable echo server for testing
        t = tcpclient("localhost", 4000);
    end

    % Critical section where callbacks should not interrupt
    ALLOW_CALLBACKS = false;
    for n = 1:20 % Example critical loop
        fprintf('Critical operation in progress: Iteration %d\n', n);
        if Do_TCPIP
            % Simulate a critical TCP/IP operation
            writeline(t, "This is a critical message.");
            response = readline(t); % Assuming echo server, expect immediate response
            fprintf('TCP/IP Echo Response: %s\n', response);
        end
        pause(1); % Simulate time-consuming operation
    end
    
    %Callbacks re-enabled
    ALLOW_CALLBACKS = true;

    % Wrap up...
    if Do_TCPIP
        clear t; % Close and clear the TCP/IP connection
        echotcpip('off'); % Disable echo server
    end
    delete(hFigure); % Close the GUI
    fprintf('Critical section completed. Callbacks re-enabled.\n');
end

function ACallBack(~,~)
    global ALLOW_CALLBACKS;
    if ~ALLOW_CALLBACKS
        fprintf('Callback execution is currently disabled.\n');
        return;
    end
    % Callback code that should be executed when allowed
    fprintf('Callback executed: Main loop potentially interrupted.\n');
end

I hope this helps!