Question

What could be causing an out of memory exception in the code below? My program was running for a few hours and then died. The code only sends/receives a very small amount of data each time, so there are no huge files or strings going over the wire or coming back. The code sends and receives from the server every 3 seconds or so.

private void Read()
{
    string postData = "Name=John"
    using (HttpWebResponse response = SendRequest(new Uri(@"someWebSitehere"), postData))
    {
         Stream stream = response.GetResponseStream();
         StreamReader reader = new StreamReader(stream);
         responseFromServer = reader.ReadToEnd();　　IT THROWS OUT OF MEMORY HERE
     　   stream.Close();
    ｝
}

private HttpWebResponse SendRequest(Uri uri, string postData)
{
    lock (SendRequestLock)
    {
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);

        req.Method = "POST";
        req.CookieContainer = new CookieContainer();
        req.Proxy = null;
        UTF8Encoding encoding = new UTF8Encoding();
        byte[] byte1 = encoding.GetBytes(postData);

        // Set the content type of the data being posted.
        req.ContentType = "application/x-www-form-urlencoded";

        // Set the content length of the string being posted.
        req.ContentLength = byte1.Length;

        req.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.0.3705;)";
        req.Method = "POST";
        req.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
        req.Headers.Add("Accept-Language: en-us,en;q=0.5");
        req.Headers.Add("Accept-Encoding: gzip,deflate");
        req.Headers.Add("Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7");
        req.KeepAlive = true;
        req.Headers.Add("Keep-Alive: 300");
        using (Stream stream = req.GetRequestStream())
        {
            stream.Write(byte1, 0, byte1.Length);
        }
        return (HttpWebResponse)req.GetResponse();
    }
}

Answer 1

You’ll want to dispose of the IDisposable classes Stream and StreamReader:

using (Stream stream = response.GetResponseStream())
{
    using (StreamReader reader = new StreamReader(stream)) 
    {
        responseFromServer = reader.ReadToEnd();　　//IT THROWS OUT OF MEMORY HERE
    }
}

Classes that implement IDisposable generally have external resources that they will hang onto unless you call Dispose() (or, same thing, put it inside a using block). It’s likely that those classes are leaking memory each time your block of code runs, hence the “out of memory” exception after some time.

It’s worthwhile reading MSDN’s notes on IDisposable.