fclose(obj) does not work immediately

I have a TCPIP conncetion and I send and read data with an app designer application.

I use fclose(obj) function, but the tcp connection does not close immediately and it takes one or two minutes until it is closed.

after I close the connection I want to reopen it and I get this error:

Unsuccessful open: Address already in use:

connect

Answer 1

[Image Analyst]

In the help for tcpclient() and fclose(), I don't see any mention of using fclose() to close a tcp session. It says this:

Close the connection between the TCP/IP client and the remote host by clearing the object. Turn off the echotcpip server.

clear t
echotcpip("off")

You might also call flush() before closing just to see if that speeds anything up.

[SRii]

Thanks for your answer.

I used flush(), but it says this function does not work for tcp ip objects.

also I used clear and echotcpip.. still not working. It takes a while that matlab releases tcp connection

[Image Analyst]

Are you using Windows? Maybe you can bump up the priority of your process so it will process that message sooner. Perhaps now when the close signal is sent it just take a while for the operating system to get around to processing it because it thinks it's working on higher priority things.

[SRii]

yes I'm using windows. how should I do that?

[Image Analyst]

Google it. First hit:

https://windowsreport.com/task-manager-set-priority/

[SrinivasHarsha]

Hi Image Analyst,

we need a help from you

can you send a response to my mail if possible.

we will contact you reg: image processing help

my mail id: [e-mail]

[SrinivasHarsha]

Hi Image Analyst,

we need a help from you

can you send a response to my mail if possible.

we will contact you reg: image processing help

my mail id: [e-mail]

[Walter Roberson]

Image Analyst does not volunteer email support. He will not help you through email.

Answer 2

[Walter Roberson]

When you use tcp the default keep-alive timeout is 2 hours https://docs.microsoft.com/en-us/windows/win32/winsock/so-keepalive . When you close a socket it can take until the end of that interval before the system clears the connection.

This is an inherently hard problem in reliable asynchronous communications.

When your end says Bye, how do you know that the other end heard you so that you can remove the local resources? Well, you can require that the other end sends you a response. Can the other end clear their state immediately after sending the response? Well, how does the other end know that your end received the response? So your end has to send a response to the response. But how does your end know that the other end heard the response to the response? It has to send a response to that....

If you go through the logic, it turns out that for reliable service, you need an indefinite chain of acknowledgement of acknowledgement. So in practice you need a timeout system. If your end does not receive the last packet in the shutdown sequence but the other end has already removed the state then you might need to wait through the timeout period. This is not a MATLAB issue: it happens for all reliable asynchronous communications protocols.

[SRii]

Thanks a lot for your complete explanation.

I have a Demo application which is written by C# I think. I am going to rewrite this application my self.

when I close connection in this c# demo software, it closes port immediately. same port same ip same device. but my matlab app has a problem. maybe it's because of priority or something