HttpWebRequest GetRequestStream SystemException after several calls randomly

Question

I have a program in C# .NET 3.5 CompactFramework that requests data from a C# WebService:

    public SynchronisationResult<J> Get<J>(IEnumerable<DomainProxy> existingObjects, string controller, string parameters) where J : IdJsonObject)
{
            string existingObjectsJson = JsonConvert.SerializeObject(existingObjects);
            string url = GenerateUrl(controller, parameters);
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
            request.ContentType = "text/json";
            request.Method = "POST";
            request.KeepAlive = false;
            request.ProtocolVersion = HttpVersion.Version11;
            request.Timeout = 60000;
            request.ContentLength = existingObjectsJson.Length;

            using (Stream requestStream = request.GetRequestStream())
            {
                using (var streamWriter = new StreamWriter(requestStream))
                {
                    streamWriter.Write(existingObjectsJson);
                    streamWriter.Flush();
                    streamWriter.Close();
                }
                requestStream.Close();
            }

            using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
            {
                string responseData = "";
                using (var streamReader = new StreamReader(response.GetResponseStream()))
                {
                    responseData = streamReader.ReadToEnd();
                }
                if (response.StatusCode == HttpStatusCode.OK)
                {
                    result = JsonConvert.DeserializeObject<SynchronisationResult<J>>(responseData);
                }
                else
                {
                    throw new Exception(responseData);
                }
                response.Close();
            }
}

I can call this method several times with different parameters (different controllers on the WebServer) and suddenly everything gets stuck. The application does not react anymore, when i press PAUSE in Visual Studio i see the program pointer at the location

using (Stream requestStream = request.GetRequestStream())

Sometimes a SystemException is thrown in Timer.ring of System.Net.Connection..., although in case, the application does not continue to run, even not by bubbling the exception to the next catch-Block. This means, that i have to reset the device it does never continue to run.

I have tried the following changes to solve the problem:

• request.KeepAlive = true / false
• request.Pipelines = true / false
• ServicePointManager.DefaultConnectionLimit = 1000;
• request.AutomaticDecompression = DecompressionMethods.GZip or nothing

Nothing, the request works fine in Postman for example. Weird thing is, if i implement this in a for loop, asking for about 200 objects to be updated it crashes faster. In case i implement the request method on a button click and click it with a frequency of about 10 seconds it works way longer. I tried with a development IIS backend on port 888, with a production machine on port 80, firewall locally is turned off. There is no certain request that fails it could be a request for type A or B or C,... each run is different.

Would someone explain:

a) why code gets stuck and does not continue?

b) why code gets stuck even when an exception is thrown

c) how to configure ServicePointManager or Request to get things working properly

EDIT: This is the Exception that sometimes occurs when request.GetRequestStream() is executed:

at System.Threading.Timer.startTimer(UInt32 dueTime)
at System.Threading.Timer.Change(UInt32 dueTime, UInt32 period)
at System.Threading.Timer.Change(Int32 dueTime, Int32 period)
at System.Threading.ThreadPool.QueueUserWorkItem(WaitCallback callBack, Object state, Boolean IsHttpRequest)
at System.Net.Connection.actionSending()
at System.Net.Connection.changeState(ConnectionState state)
at System.Net.Connection.transitionRequestSent(Event e)
at System.Net.Connection.processEvent(Event e)
at System.Net.Connection.actionRequestSent()
at System.Net.Connection.changeState(ConnectionState state)
at System.Net.Connection.transitionIdle(Event e)
at System.Net.Connection.processEvent(Event e)
at System.Net.Connection.submitRequest(HttpWebRequest request)
at System.Net.ServicePoint.SubmitRequest(HttpWebRequest request, String connGroupName)
at System.Net.HttpWebRequest.SubmitRequest()
at System.Net.HttpWebRequest.finishGetRequestStream()
at System.Net.HttpWebRequest.GetRequestStream()

Answer 1

I was also stuck on this issue for couple of days. Finally what I found was if I run Fiddler in the background there was no exception thrown in the request.GetRequestStream(). Which means this is something related to the connection pool where fiddler is handling this. So I did some research and found the below link which solved my issue:

https://www.telerik.com/blogs/help!-running-fiddler-fixes-my-app-

Also after the request is completed make sure you abort that as well. What I did is:

if (webrequest != null) webrequest.Abort();

For me everything is working fine now.