C# .Net Serial Port "port.BytesToRead" sometime returns 0 when the "port.dataReceived" is called

Question

I am writing a C# program to poll data from Arduino serial port which generates data through "serial.println". In C# program, I found "port.BytesToRead" sometimes returns 0 even though the "port.dataReceived" is called. As a result, it prints out the error message that I requested it to print. However, if the "port.BytesToRead" returns 0, it stops me from polling the data from the main polling loop when I should. Any suggestions to the cause of the error and how to fix that?

        _serialPort = new SerialPort();
        _serialPort.PortName = "COM7";//Set your board COM
        _serialPort.BaudRate = 9600;

        _serialPort.ReadTimeout = 500;
        _serialPort.WriteTimeout = 500;

        _serialPort.DtrEnable = true;
        _serialPort.RtsEnable = true;

        _serialPort.DataReceived += Watch_BLE_DataReceived;       
        
        private void Watch_BLE_DataReceived(object sender, EventArgs arg)
        {
            SerialPort port = sender as SerialPort;

            if (port == null)
            {
                return;
            }

           
            if (!(port.BytesToRead > 0))
            {
                // print error
            }
                
        }

In the main function, I write a polling loop like:

        while (true)
        {   
            
            try
            {
                if (!_serialPort.IsOpen)
                {
                    
                    _serialPort.Open();

                }
            }
            catch (Exception e)
            {

                continue;
            }

            try
            {
                
                

                if (_serialPort.BytesToRead > 0) {
                    // process read data
                }
            }
        }

SnoreGore · Accepted Answer · 2023-06-10 23:00:07Z

1

Why are you both polling and using the SerialPort.DataReceived event? That's making little sense.

Decide upon only one approach, checking for and consuming the incoming data either by using a polling loop or by using the SerialPort.DataReceived event.

Because you are currently using both polling and the SerialPort.DataReceived event together, your program quite likely suffers from a race condition.

The SerialPort instance recognizes data incoming on the serial port, buffers that data in its receive buffer and raises the DataReceived event. And what is probably happening then sometimes is that the timing of the current iteration of your polling loop is just such that it manages to read and thus empty the receive buffer before the DataReceived event handler is getting around to check the port.BytesToRead value. This then leads to the situation where the DataReceived event handler sees no bytes to read because the polling loop was just a little quicker that time.

edited Jun 10, 2023 at 23:00

answered Jun 10, 2023 at 22:27

SnoreGore

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1 Comment

universe123 Over a year ago

I am using the handler to check whether the port.BytesToRead is actually a good check for whether data is in the buffer. Your explanation only explains the case where DataReceived event not fired, but doesn't explain the case I am asking for, where port.BytesToRead is 0 while DataReceived event is fired though.

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