MATLAB: exiting infinite loop without using global variable in GUI

Question

Background: I have several portion in an GUI to handle different tasks. In 1 portion (portion1) I have text input and send button. So once I will click send it would send one data to my serial port. Another portion (portion2) would receive signal from serial port which have been received from other devices. Both the portions are using two buttons; one to start the work of that particular portion and one to stop the work. I have used global variables and while loop (with boolean) to exit the infinite loop, as I need to send the data or receive data continuously.

My question: Problem is when I am using global variables and the above mentioned way of using infinite loop, if I click portion1, portion1 will start iterate. Now if I click portion2 then portion1 will be stopped. But I need to use them both at the same time and both of them will continuously send and receive data until I click other button (s) to exit the infinite loop.

My sample code for clarification:

function send_Callback(hObject, eventdata, handles)
  global firstFlag;
  firstFlag = true;
  while firstFlag
  %Required codes
  end

function haltSend_Callback(hObject, eventdata, handles)
  global firstFlag;
  firstFlag = false;

function receive_Callback(hObject, eventdata, handles)
  global secondFlag;
  secondFlag = true;
  while true
  %Required codes
  end

function stopReceive_Callback(hObject, eventdata, handles)
  global secondFlag;
  secondFlag=false;

I have tried to find a solution referring to internet, but most of the solutions are using global variable. It would be better if I could work without global variables. But even if my requirements are fulfilled (as per my question) it would work.

Answer 1

Global or not is not the issue here.

Callbacks in Matlab all run on the same thread. So when callback1 is running and you trigger callback2, callback2 will interrupt callback1. callback1 will then only proceed once callback2 is finished. You can only slightly modify this procedure using the BusyAction property:

http://www.mathworks.de/de/help/matlab/ref/uicontrol_props.html#bqxoija

But this won't help in your case. In a "proper" programming language, you'd have a sending and a receiving thread running in parallel. You can't do this matlab however - unless you're e.g. willing to write java-code.

If you want to stick with matlab, the closest to thread would be timers. These would replace your while loops. E.g. as in the following minimalistic example:

function cbtest()

    try close('cbtest');end
    f = figure('name', 'cbtest');

    % create the timers:
    period = 0.2; % period in seconds, in which the timer shall execute
    sendTimer = timer('TimerFcn', @sendFcn, 'ExecutionMode', 'fixedDelay', 'Period', period, 'TasksToExecute', Inf);
    recvTimer = timer('TimerFcn', @recvFcn, 'ExecutionMode', 'fixedDelay', 'Period', period, 'TasksToExecute', Inf);

    uicontrol(f, 'position', [10 10 100 25], 'Callback', @(a,b) start(sendTimer), 'string', 'start1');
    uicontrol(f, 'position', [120 10 100 25], 'Callback', @(a,b) stop(sendTimer), 'string', 'stop1');

    uicontrol(f, 'position', [10 50 100 25], 'Callback', @(a,b) start(recvTimer), 'string', 'start2');
    uicontrol(f, 'position', [120 50 100 25], 'Callback', @(a,b) stop(recvTimer), 'string', 'stop2');
end

function sendFcn(hTimer, timerEvt)
    % your send-loop-code
    disp('sending');
end

function recvFcn(hTimer, timerEvt)
    % your receive-loop-code
    disp('receiving');
end

sendFcn and recvFcn here then should contain the code you have within your according while loops. You can of course lower the period to your needs, I chose the above for testing purposes.

Answer 2

Your problem is that you're executing the loop inside the Callbacks. So when the second button is clicked, the second callback will start and loop infinitely, until it is ended. The first loop will wait for the second Callback to terminate until it can resume. What you need is a main program where you execute your loop. Nesting the Callbacks will make sure they can access and change the local variables without making them global. If you're fine with building a GUI programmatically, try this:

function main()
  sendFlag = false;
  receiveFlag = false;

  while true
    if sendFlag
      % Your Sending code
    end
    if receiveFlag
      % Your Receiving code
    end
  end

  function send_Callback(~,~,~)
    sendFlag = true;
  end

  % other Callbacks

end

Then in the Callbacks for your Buttons (you could use Toggle Buttons by the way), you simply set the sendFlag and receiveFlag, respectively.

Using GUIDE, you want to use toggle buttons. I don't exactly know how GUIDE handles the OpeningFcn, so you should probably put a "Start" button into your GUI which basically executes the above program with a few changes:

function startbutton_Callback(hObject,~,handles)
  while true
    handles = guidata(hObject); % Updates handles structure

    sendFlag = get(handles.sendtoggle, 'Value');
    if sendFlag
      % Your Sending code
    end

    receiveFlag = get(handles.receivetoggle, 'Value');
    if receiveFlag
      % Your Receiving code
    end
  end

Also, create send and receive toggle buttons and set their 'Min' to 0 and 'Max' to 1. This will make them switch their 'Value' property (which you read in the above loop) between 0 and 1 when you click them. In the Callback, you can change what they display:

function send_Callback(hObject,~,handles)
  on = get(hObject,'Value');
  if on
    set(hObject, 'String', 'Stop sending');
  else
    set(hObject, 'String', 'Start sending');
  end
  guidata(hObject,handles); % Update GUI data

Now your main function, which starts when you click the start button, runs the loop and just checks the toggle buttons' states to determine whether to send and receive.