QSerialPort with Thread miss same data

jsulm

@Gokhan You should post you code without QThread. Multi threading isn't needed actually as you can use signals/slots (not events) and just makes you code more complex.

mrdebug

Please try to download this source of an application Qt based that uses QSerialPort
https://www.linux-apps.com/content/show.php/QtComPort?content=142378
It uses event approach. Please have a look that if it can help you.
The application can put in bridge two serial ports in order to monitor what is passing through.

Gokhan

@jsulm and @mrdebug I just now tried the terminal program in examples and added only a few lines code in order to start the MCU. It too missed data.
If USB_Can converter's red led is on, it means that there is a missing transfer. However, while Hercules that is a serial port terminal program using, there is no missing data.
You can see this in below video.
Link : https://drive.google.com/file/d/0B7WvtYBLRY0YVFFmRzZvWWZKVFk/view

mrdebug

I suggest you to use QtComPort and watch the output in hex format.
After that please post the output.
Which kind of protocol are you using? Is there a header, a footer, a crc...???

J.Hilk

@Gokhan I would say that is expected behaviour. By "resizing" the gui your main thread is blocked/busy with that.

But the statement is still true, QSerialport does not loose data.
Your device probably runs in an timeout because it gets no answer from your serialport, because the old data was not collected.

Seems like Threading your SerialPort-communictation is the only option in this particular case.

Gokhan

@J.Hilk However, when I periodically read the serial port buffer via a thread for 100 ms, it returns the null data, so the serial port buffer is seeming empty and the device is giving the error again.

J.Hilk

@Gokhan
I downloaded your code,

take a look here and here and create your QThread, how it should be done ;-)

And don't use the blocking waitForXxx functions, use signal slots with connects.

Gokhan

@J.Hilk thank you, actually, first I wrote it like in my first post, and after that, I saw that it's not working, started to try all possibilities. I guess that there is a bug in Qt, because the assignee wrote a bug about this subject.
https://bugreports.qt.io/browse/QTBUG-61237

@mrdebug I have gotten lots of errors with this Project QtComPort, I didn't compile it, guess that it needs a Linux PC.

mrjj

I guess that there is a bug in Qt, because the assignee wrote a bug about this subject.
https://bugreports.qt.io/browse/QTBUG-61237

Hi.
It is not in Qt. its a windows/platform thing.
It is a known thing with windows.
It applies to all apps. Also those not written in Qt.
https://stackoverflow.com/questions/18041622/how-do-i-stop-windows-from-blocking-the-program-during-a-window-drag-or-menu-but

Gokhan

@mrjj However, another program is working well like you can see my video. Is this big problem for application? e.g my application must immediately give an error in this condition and stop the communication.
What do you suggest me in order to solve this problem? I had used the LabVIEW before and developed like this application, it had worked flawlessly.

mrjj

@Gokhan
The normal solution is to use a thread.
Then it wont be interrupted when dragging/resizing.

kuzulis

@Gokhan,

I have added for you an example "qsp-no-freeze-workaround-windows" which demonstrates how it should work with threads!

Gokhan

@kuzulis Thank you very much, it's really working well. My first code that is in my first post here looks like this, but there is one different between them, it is inheritance. Is this a problem?

Also, how should I use qmutex between two classes in order to syncrhronşze? It's not declared the static and global variable is not recommended for it.

mrjj

@Gokhan said in QSerialPort with Thread miss same data:

how should I use qmutex between two classes in order to syncrhronşze?

What do you need to synchronize ?
You could use signals to tell other class about new data.

Gokhan

@mrjj I must convert the received data to be meaningful, then will show these in tableview. I thought these data periodically will be converted and shown in two different thread for 100milisec.

mrjj

@Gokhan
Hi, you cannot use any widget in any other thread than the main thread.
But using a signal to tell the some other class about the formatted data will work super.
https://stackoverflow.com/questions/15276628/send-data-from-worker-thread-to-gui-thread-in-qt

Gokhan

@mrjj Don't I need a mutex if use a signal to tell other class? By the way, thread appends the raw array and after slot received a signal, it will convert the raw array and then clear it. Doesn't it need a mutex to do this process?

mrjj

@Gokhan
The signal will contain a copy of the data so in most cases you do not need to protect it.
But depends on your design. If its possible that array is being written to , while you clear it then, yes
you need concurrency control.

Gokhan

@mrjj Sometimes the array can be huge size, e.g 100K and conversion can take a long time furthermore it will show these data in tableview. Do not you think it takes a long time? Then which method do you suggest me to use?

mrjj

@Gokhan
Ok, if that big, then a processing/convert thread seems a good idea.