I have a Socket Server and a client, but the server will not
always online, so the client will try to connect to server at a proper
inteval, when the server is available, the client will connect to it
auto.
       I design a thread to do this work, every 1 second, it check
Socket.Connected, if it becomes False, the thread invoke asynchrous
BeginConnect, WHEN I TEST THE CLIENT WITHOUT SERVER RUN,
that is to say, EndConnect will never connect to the server. BUG'S
APEAR, after 2 to 3 minutes,
System throw following exception:

System.NullReferenceException was unhandled
  Message="Object reference not set to an instance of an object."
  Source="System"
  StackTrace:
       at System.Net.Sockets.Socket.ConnectCallback()
       at System.Net.Sockets.Socket.RegisteredWaitCallback(Object
state, Boolean timedOut)
       at
System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object
state, Boolean timedOut)

Any one can help me to treat the problem?
BTW, Development Evn.
..NET Framework 2.0
Windows2003 SP1
VS2005

Test Code As Follow;
private void Form1_Load(object sender, EventArgs e)
        {
            while (true)
            {
                try
                {
                    // if i must switch to Socket.Connect(...)?
                    FSocket.BeginConnect("127.0.0.1", 6500, new
AsyncCallback(ConnectCallback), this);
                }
                catch
                {
                }
                System.Threading.Thread.Sleep(1000); // Sleep(100)
will see the exception more quick
            }
        }
        static void ConnectCallback(IAsyncResult ar)
        {
            try
            {
                Form1 This = (Form1)ar.AsyncState;
                This.FSocket.EndConnect(ar);
            }
            catch (SocketException)
            {
            }
        }

zzppallas@gmail.com wrote:

>         I have a Socket Server and a client, but the server will not
> always online, so the client will try to connect to server at a proper
> inteval, when the server is available, the client will connect to it
> auto.
>        I design a thread to do this work, every 1 second, it check
> Socket.Connected, if it becomes False, the thread invoke asynchrous
> BeginConnect, WHEN I TEST THE CLIENT WITHOUT SERVER RUN,
> that is to say, EndConnect will never connect to the server. BUG'S
> APEAR, after 2 to 3 minutes,
> System throw following exception:
> 
> System.NullReferenceException was unhandled
>   Message="Object reference not set to an instance of an object."
>   Source="System"


So, what variable is null?  I suspect it's the Form1.FSocket member 
variable, but if you're going to ask a question, you need to be specific 
about the error.

You also did not post all of the code.  In particular, you didn't post 
the code that polls Socket.Connected, so that we can see what you do in 
that case.  I'm guessing that somewhere along the line, you set 
Form1.FSocket to null, causing the exception.

Now, all that said: it's a bad idea to poll Socket.Connected at all. 
You should simply treat the connection normally unless there is an error 
when using the socket, and handle the lost connection at that point, 
reattempting a connect.  Socket.Connected isn't going to change state 
until such an error occurs anyway, so you aren't gaining anything by 
polling it.

Also, rather than calling BeginConnect() every second, you should only 
reattempt a connection when the previous attempt has actually failed (it 
will timeout for a TCP socket).  So in the ConnectCallback() method, if 
there is an exception calling EndConnect() (which indicates a failure to 
connect), call BeginConnect() again there.

Pete

On Aug 9, 1:45 am, Peter Duniho  wrote:

> zzppal...@gmail.com wrote:
> >         I have a Socket Server and a client, but the server will not
> > always online, so the client will try to connect to server at a proper
> > inteval, when the server is available, the client will connect to it
> > auto.
> >        I design a thread to do this work, every 1 second, it check
> > Socket.Connected, if it becomes False, the thread invoke asynchrous
> > BeginConnect, WHEN I TEST THE CLIENT WITHOUT SERVER RUN,
> > that is to say, EndConnect will never connect to the server. BUG'S
> > APEAR, after 2 to 3 minutes,
> > System throw following exception:
>
> > System.NullReferenceException was unhandled
> >   Message="Object reference not set to an instance of an object."
> >   Source="System"
>
> So, what variable is null?  I suspect it's the Form1.FSocket member
> variable, but if you're going to ask a question, you need to be specific
> about the error.
>
> You also did not post all of the code.  In particular, you didn't post
> the code that polls Socket.Connected, so that we can see what you do in
> that case.  I'm guessing that somewhere along the line, you set
> Form1.FSocket to null, causing the exception.


no where to set Form1.FSocket to null;
U can Assign a new Socket to it at constructor,and run the test
program,
first connects failed but the exception can be catched.
after 3 to 5minutes an UNHANDLED EXCEPTION will be thrown,and the
callstack will give u no useful message, only the Exception Window u
can extract exception message,
the exception throwed from another unnamed thread.


> Now, all that said: it's a bad idea to poll Socket.Connected at all.
> You should simply treat the connection normally unless there is an error
> when using the socket, and handle the lost connection at that point,
> reattempting a connect.  Socket.Connected isn't going to change state
> until such an error occurs anyway, so you aren't gaining anything by
> polling it.
>
> Also, rather than calling BeginConnect() every second, you should only
> reattempt a connection when the previous attempt has actually failed (it
> will timeout for a TCP socket).  So in the ConnectCallback() method, if
> there is an exception calling EndConnect() (which indicates a failure to
> connect), call BeginConnect() again there.
>
> Pete


It's a test program, and u can find this UNHANDLED EXCEPTION,
maybe it's a .netframework Socket bug.

Pallas wrote:

> no where to set Form1.FSocket to null;


Well, something is getting set to null.


> U can Assign a new Socket to it at constructor,and run the test
> program,


Please stop abbreviating.  If you can take the time to write anything, 
you can take the time to write words correctly.  Many people, myself 
included, find it difficult to try to interpret "IM speak".  You will 
find the rate of response to your questions is proportional to the 
quality of the text you write.  If you can't be bothered to write in 
plain language, other people won't bother to read what you wrote, never 
mind try to help.

Now, that said.  What test program?  You haven't posted a test program.


> first connects failed but the exception can be catched.
> after 3 to 5minutes an UNHANDLED EXCEPTION will be thrown,and the
> callstack will give u no useful message, only the Exception Window u
> can extract exception message,
> the exception throwed from another unnamed thread.


I doubt that it's true that there is no null reference anywhere in the 
call stack, given that the exception occurred.  In fact, 
NullReferenceExceptions are usually very easy to figure out, because all 
you have to do is find the variable that's null and shouldn't be.

Still, if you post no code that anyone can test with, it is impossible 
for anyone else to make an attempt to help you (other than explaining a 
better way to write the code you did post, which I've already done).


> It's a test program, and u can find this UNHANDLED EXCEPTION,
> maybe it's a .netframework Socket bug.


It's not a .NET Framework Socket bug.  What the bug is, I can't say. 
You haven't bothered to post code that anyone could use to test to 
explain to you what the problem is.  But I'm sure this is a bug in your 
own code, especially given the code you've already posted.

If you are unwilling to post a concise-but-complete example of code that 
reliably reproduces the problem, then you should at least try making the 
changes I suggested to see if that fixes your problem.  The code you 
posted is very wrong.

Pete