Exiting form readline() in TCPIP server before timeout occurs

I am using the App Designer to develop a TCPIP server (OS: Windows 11). I have to receive command strings from a remote Cient but I must be free at any moment to stop the server and exit from the app by using a specific button: STOPbutton. This is my code:

%Code that executes after component creation

function startupFcn(app)

app.myServer = tcpserver("::",4000,"Timeout",1000);

configureTerminator(app.myServer,"CR")

while(1) % Infinite loop

try

command = readline(app.myServer); % A command string is received

% The command is parsed

%

%

end

end

% Button pushed function: StopButton

function STOPButtonPushed(app, event)

clear app.myServer

app.delete

end

Debugging the script in the App Designer pushing the STOPbutton (before the 1000 secs timeout expires) the result is not the expected one. The UIfigure user interface closes but the debugging session doesn't stop and the only way to restart the session is by using a ctrl-C in the Matlab command window.

This is the message i am getting in the command window:

Operation terminated by user during matlabshared.asyncio.internal.Stream/wait
In matlabshared.transportlib.internal.asyncIOTransportChannel.AsyncIOTransportChannel/waitForDataAvailable
In matlabshared.transportlib.internal.asyncIOTransportChannel.AsyncIOTransportChannel/readUntil
In matlabshared.transportlib.internal.GenericTransport/readUntil
In matlabshared.transportclients.internal.StringClient.StringClient/readRaw
In matlabshared.transportclients.internal.StringClient.StringClient/read
In matlabshared.transportlib.internal.client.ClientImpl/readline (line 139)
data = read(obj.StringClient, precision);
In matlabshared.transportlib.internal.client.GenericClient/readline (line 631)
data = readline(obj.ClientImpl, varargin{:});
In tcpserver.internal.TCPServer/readline (line 595)
data = readline(obj.Client,varargin{:});
In Mat_server_app/startupFcn (line 37)
command = readline(app.myServer);
In matlab.apps.AppBase/runStartupFcn (line 69)
ams.runStartupFcn(app, startfcn);
In Mat_server_app (line 149)
runStartupFcn(app, @startupFcn)

It seems that by deleting the tcpserver object the readline function is not terminated and some process remains active.

By compiling a Standalone Destktop App and running the App the anomaly has been confirmed. By pushing the STOPbutton the UIfigure user interface closes but a the process related to the App is always running (as reported by the by the Windows 11 task manager ). The only way to restart the server is to kill such process in the task manager.

Any idea about how to force the readline process to end before its timeout expires ?

Answer 1

[chrisw23]

try to implement the BytesAvailableFcn callback before starting the readline function

flush the buffer and delete ther server when the app will be closed

[Vincenzo Genovese]

It is not clear to me the role of BytesAvailableFcn callback. What exactly should the callaback do since I'm interested in reading a string by the readline()? Please, take in account that I used: configureTerminator(app.myServer,"CR").

[chrisw23]

You call readline() without knowing if there's any data to be read and this probably results in wait/timeout state. This may be the effect you see when trying to close your app.