Why is this SocketException not caught by a generic catch routine?

Question

Our company provides a network component (DLL) for a GUI application.

It uses a Timer that checks for disconnections. If it wants to reconnect, it calls:

internal void timClock_TimerCallback(object state)
{
  lock (someLock)
  {
    // ...
    try
    {
         DoConnect();
    }
    catch (Exception e)
    {
        // Log e.Message omitted
        // Raise event with e as parameter
        ErrorEvent(this, new ErrorEventArgs(e));
        DoDisconnect();
    }
    // ...
  }
}

So the problem is, inside of the DoConnect() routine a SocketException is thrown (and not caught). I would assume, that the catch (Exception e) should catch ALL exceptions but somehow the SocketException was not caught and shows up to the GUI application.

protected void DoConnect()
{
    //
    client = new TcpClient();
    client.NoDelay = true;
    // In the following call the SocketException is thrown
    client.Connect(endPoint.Address.ToString(), endPoint.Port);
    // ... (login stuff)
}

The doc confirmed that SocketException extends Exception. The stacktrace that showed up is:

TcpClient.Connect() -> DoConnect() -> timClock_TimerCallback

So the exception is not thrown outside the try/catch block.

Any ideas why it doesn't work?

Answer 1

I wrote a little program and was unable to reproduce, a SocketException was caught inside a TimerCallback just fine.

So I suggest you re-think your analysis, the problem may not be what you think it is. A few suggestions:

• run it outside the Timer. T|hat takes the threading out of the loop.
• run it in the debugger. Where does the exception really occur?
• step through the exception handling. Is ErrorEvent doing what it should?

Answer 2

If ErrorEvent really raises another exception (per the comment), then DoDisconnect() is never executed.

Otherwise, the exception you see might be coming form DoDisconnect()

Answer 3

Could you post the DoConnect() code?

Also things to try: Can you catch it in the DoConnect()? Try catching the specific exception instead of just the generic. How does it react if you use debug mode?

Answer 4

Your timClock_TimerCallback isn't called in the same thread as the catch-statement wants to catch an exception. You should catch the exception inside timClock_TimerCallback and then call a method which invokes itself and then rethrow the exception in the right thread.

Not sure this will work, but you could give it a try.