I am writing a ASP.NET based REAL TIME COMET server. But project is now 98% complete. But there is 1 mysterous thing I can not find anywhere.

Actual code is quite long, so to reproduce the problem I wrote following simple handler.

    public class CometHandler : IHttpAsyncHandler
    {           
        #region IHttpAsyncHandler Members

        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
        {     
            // TESTING
            AsyncResultWrapper ar = new AsyncResultWrapper(cb, extraData);

            if (context.Request.RawUrl.Contains("iframe")) {

                // save this persitent connection dont close
                context.Response.Write(CometServer.IFramePrologue);
                context.Response.Write("<script>callback(-2,\"\")</script>");
                context.Response.Flush();
            } else if (context.Request.RawUrl.Contains("connect")) {

                // save this persitent connection dont close
                context.Response.Write("<script>callback(-2,\"\")</script>");
                context.Response.Flush();
            } else {
                // close other connections
                ar.SetCompleted();
            }
            //
          
            return ar;
           
        }

        public void EndProcessRequest(IAsyncResult result)
        {            
           
        }

        #endregion

        #region IHttpHandler Members

        public bool IsReusable
        {
            get { return false; }
        }

        public void ProcessRequest(HttpContext context)
        {
            throw new Exception("This method is never called by runtime.");
        }

        #endregion

        #region AsyncWrapper

        private class AsyncResultWrapper : IAsyncResult
        {
            private bool mIsCompleted;
            private AsyncCallback mCallBack;
            private object mState;

            public AsyncResultWrapper(AsyncCallback callback, object state)
            {
                mIsCompleted = false;
                mCallBack = callback;
                mState = state;
            }

            #region IAsyncResult Members

            object IAsyncResult.AsyncState
            {
                get { return mState; }
            }

            WaitHandle IAsyncResult.AsyncWaitHandle
            {
                get { return null; }
            }

            bool IAsyncResult.CompletedSynchronously
            {
                get { return false; }
            }

            bool IAsyncResult.IsCompleted
            {
                get { return mIsCompleted; }
            }

            #endregion

            public void SetCompleted()
            {
                mIsCompleted = true;
                if (mCallBack != null) {
                    mCallBack(this);
                }
            }
        }        

        #endregion
    }

The problem is this:

1. I connect to this handler via XMLHttpRequest object, this connection doesn't close for about 2 - 5 minute.

2. I send short requests to this handler via XMLHttpRequest object

I repeat this process on 1 firefox, 2 IE window. (total of 3 clients).

But on the third client after I do step# 1, then when I send second request (step # 2) request doesn't come back. It hangs.

I am assuming it is not on the client side, and also I didn't implement any of Session State interfaces.

Please HELP ME, I will appreciate so MUCH!

Is there an actual asynchronous operation that you're starting? Your code doesn't show it. In fact,the code, as posted, does not need to be async.

Yes, I have created custom THREAD POOL, and queueing the items there. So I was first wondering the problem was locking issues with my thread pool, so I removed it and checked. It was ok. 

This code i posted is not my real Comet Server application code. They are not relevant pieces, I checked. What is important is when new request comes in I somehow keeps or saves some connections in list and close some connections immediately.

I know I compacted the code, IT IS JUST A TEST CASE. It doesn't have to include real ASYNC operation. 

And also, today I found some strange thing, 

Is it ok to call HttpContext's Resonse.Write on any thread, or I should accumulate all data in async thread and DO THE WRITE operation in Async handler's EndResponse callback method?

And also I am using 2 XMLHttpRequest object on the client side. 

1. First one connects to this async handler like /connect/Comet.ashx  etc .. So the server will not immediately close this connection but keep it

2. I send short requests on the other one, so server will close it immediately after processing.

My platform is: IIS 7, Vista Home Premium, and also tested on Windows XP PRO and IIS 6.

All the same, third clients 2ND XMLHttpRequest hangs after the first one. I am really wondering why.

Is this Write, Flush operations causing locks, I dont know, It is really hard to find for me. PLEASE HELP, again

I need to finish this very soon,

If you need any other information, please let me know.

If you didn't know it before, then you certainly know it now: multithreaded programming is not easy.

I doubt that anyone could help you on this without seeing all of the code. Certainly, I will not have time to help you, even if you post the code - like I said, this is not easy stuff.

One little bit of advice I'd give is to make sure that the ThreadStart method, or any other async code, is surrounded by a try/catch block. Otherwise, an unhandled exception will quietly terminate the thread, and you'll have no idea what happened. Make sure you catch the exception, log ex.ToString() somewhere thread-safe (like the Windows event log), then rethrow the exception, since you're not actually handling it.

Oh, and read the documentation on HttpRequest.Write to learn if it is thread-safe. Certainly, I wouldn't want to have multiple threads calling it without synchronization, though the synchronization may already be there.

 As you see the example code, there is no CUSTOM MULTITHREADING, I intentionally removed them all.

Problem is , you see how simple is the CODE ABOVE, but IT DOESN"T WORK the way I want it to.

There is no locking on i am making on any objects, it must work, but it doesn't