Serial Port Communication on the same Windows machine not working

Question

Excuse me, quick question:

I have this hardware setup:

Same machine: \"Com3\" -> USB -> To Serial -> To USB -> \"Com4\"

Answer 1

The problem with your code is in this line

var message = ReceiveSerialPort.ReadLine();

You block your code to wait for a line, if the line never arrives it will remain here forever or the value set to ReadTimeout

So why does the line never arrive?

The problem can be an error in WriteLine("Test");, you should handle errors, or it can be that your in are blocking your code ReadLine() before the WriteLine("Test") manage to come through, you could insert a Thread.Sleep(100) between, but this is not really improving the code.

Note: Your code will also work as is sometimes, depending on these race conditions.

This synchronized / blocking reading from serial ports seems simple in code just one line; but it creates a lot of negative side effects in your communication protocol's.

A much better solution (considering that you like to Read / Write data from a microcontroller) is to either use a thread as Yvette suggested or use asynchronously reading Stream.BeginRead (Byte[], Int32, Int32, AsyncCallback, Object) which I would prefer.

The asynchronously reading will throw an event when something is incoming on the serial port. The basic idea of this programming strategy is to not do step programming but expecting what ever result and then handle it correctly.

In communications protocol with asynchronously reading the AutoResetEvent is very useful, hence you send something, then you start the AutoResetEvent, if asynchronously the expected result is arriving you will set this event and your code can continue, if it does not arrive the AutoResetEvent will timeout and you can handle this.