Undocumented exceptions from Stream.EndWrite on HttpWebRequest request stream

[kevin cline]

I am seeing sporadic SocketExceptions being raised when calling
Stream.EndWrite on the request stream of an HttpWebRequest. The
message is:

An operation was attempted on something that is not a socket
at WriteConnectStream.NetworkWrite()
at System.Net.HttpWriteStream.Write()
at System.Net.HttpWriteStream.asyncWrite()
at WorkItem.doWork()
at System.Threading.Timer.ring()

The code looks like this:

private HttpWebRequest request = null;
private Stream requestStream = null;
...
private void StartRequest(...)
{
request = (HttpWebRequest) WebRequest.Create(...);
...
request.BeginGetRequestStream
(GetRequestStreamComplete, null);
}

private void GetRequestStreamComplete(IAsyncResult result)
{
try
{
requestStream = request.EndGetRequestStream(result);
Write PostData();
}
catch (Exception ex)
{
Cleanup();
}
}

private void WritePostData()
{
try
{
...
requestStream.BeginWrite(data, 0,
data.Length, RequestStreamWriteComplete, null);
}
catch (Exception ex)
{
Cleanup();
}
}

private void RequestStreamWriteComplete(IAsyncResult result)
{
try
{
requestStream.EndWrite(result);
// EndWrite sometimes throws SocketException
requestStream.Close();
...
}
catch (Exception ex)
{
Cleanup();
}
}

private void Cleanup()
{
try
{
...
if (requestStream != null)
{
requestStream.Close();
}
if (request != null)
{
request.Abort();
}
}
catch { }
}

Has anyone else seen this? It happens after some tens of requests have
been created and completed in short order.