Breaking change with timeout reading serial port in .NET 7 (Possible Overlapped I/O change)

[dementedmonkey]

Description

In .NET 6 and earlier, when System.IO.Ports.SerialPort.Read times out, it will throw a TimeoutException. In .NET 7, it will throw an IOException with an HResult of 0x800705B4 (1460: ERROR_TIMEOUT)

Reproduction Steps

Use the following code (substitute your own valid serial port values)

• VS2022 or .NET 7 SDK on Windows.
• Nuget Reference to System.IO.Ports version 7.0.0 (OK with eariler versions too)
• Target net7.0 to see it fail, or net6.0 to see it work.

using System;
using System.IO;
using System.IO.Ports;

class Program
{
    static void Main()
    {
        var serialPort = new SerialPort("COM42", 115200, Parity.None, 8, StopBits.One)
        {
            DtrEnable = false,
            WriteTimeout = 500,
            ReadTimeout = 500,
        };
        serialPort.Open();
        var data = new byte[100];
        try
        {
            var numRead = serialPort.Read(data, 0, data.Length);
            Console.WriteLine("Read {0}", numRead);
        }
        catch (TimeoutException)
        {
            Console.WriteLine(".NET <=6 Timed out");
        }
        catch (IOException e)
        {
            Console.WriteLine(".NET 7: IO {0}  HR:0x{1:X}", e.HResult & 0xFFFF, e.HResult);
        }
    }
}

Expected behavior

Output of .NET <=6 Timed out

Actual behavior

Output of .NET 7: IO 1460 HR:0x800705B4

Regression?

Yes. Worked for .NET 6 and 5.

You can easily test this but switching target framework. If you switch to .NET 6 you get the TimeoutException, if you switch to .NET 7 you get the IOException

Known Workarounds

Code catching the TimeoutException would have to catch the IOException check the HResult and handle it the same way.

Configuration

.net 7.0.101 Windows 11, Target X64 or x86 has the problem.
Debug or release doesn't seem to matter.

Ubuntu WSL2 with 7.0.101 does not have the problem.

Other information

This seems to be caused by changed in overlapped IO introduced in .net7

The difference can be observed here:

runtime/src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Windows.cs

Line 1505 in d099f07

SerialStreamAsyncResult asyncResult =

On .net6, the errorCode is 0, on .net7 it's 1460

The call stack invoking this function is very different on .net 6 and 7.

On .net7, AsyncFSCallback is getttiong called from PortableThreadPool and the error is set here:

runtime/src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.IO.Windows.cs

Line 262 in d099f07

errorCode = Interop.NtDll.RtlNtStatusToDosError((int)ntStatus);

On .net6, it's getting called from _IOCompletionCallback.PerformIOCompletionCallback The stack stops there, and I didn't dig any deeper to see where it's getting its parameters from.

[krwq]

See workaround for this issue in #78319 (note it was closed as dup since this one has more details)

[krwq]

Given System.IO.Ports is a nuget package and there is a workaround I suggest we just do fix in vNext.

[AlquistArj]

I also have this issue with .NET 7 serial port code (it used to work in .NET 4.8).

[hugo-lyppens]

What is the ETA for the fix? Is it just going to be a new https://nuget.info/packages/System.IO.Ports/7.0.0 or a .NET 7 fix?

[krwq]

@hugo-lyppens I can't promise anything specific to a timeline.

I couldn't pinpoint any specific change which could have regressed this so I've done some sanity testing and here are my findings:

Target Framework	System.IO.Ports version	Exception
6.0	6.0	TimeoutException
6.0	7.0	TimeoutException
7.0	6.0	IOException
7.0	7.0	IOException

Given above this doesn't look like regression was in System.IO.Ports and was likely somewhere on System.IO layer.
I'm not sure if change in System.IO was intentional or not and if we should try to workaround it in System.IO.Ports.

@dotnet/area-system-io will need to take a look and from there we can decide on the next steps