WebClient in .Net not releasing socket resources

Question

I am having problems with some simple testing code that does bulk downloads from one of our restful services. It appears that the low level socket is not being released by the call to Dispose. Here is the basic code;

foreach(...)
{
  using(WebClient client = new WebClient())
  {
    string results = client.DownloadString("http://host/request");
    client.Dispose();
  }
}

This causes an exception after 255 loops. I tried adding this line (via some suggestions form another stackoverflow post).

System.Net.ServicePointManager.DefaultConnectionLimit = 500;

Then I get an exception after 500 loops. So, it seems to me the low level socket connection is not being released.

Has anyone else seen this issue? Do you know a work around.

Thanks

The `client.Dispose()` is unnecessary, that's what the `using` is for. — Pieter van Ginkel, Nov 01 '10 at 15:55
Not an answer, but you don't need to call `Dispose` inside of a `using` block; the main point of the using block is that it ensure Dispose is automatically called. Also, you could use just one `WebClient` instance and put the `foreach` inside of the `using` block. — Jacob, Nov 01 '10 at 15:56

Aliostad · Answer 1 · 2010-11-01T16:09:59.947

WebClient does not override the Dispose it inherits from Component.

There should not be a need to call the Dispose and I do not get the error you mentioned. Please mention the other stackoverflow post.

In fact, WebClient does not keep any state that would need dsiposing and is pretty stateless. Looking at the implementation in Reflector makes it obvious that it looks after the reasources in here (method DownloadDataInternal is called from DownloadString):

private byte[] DownloadDataInternal(Uri address, out WebRequest request)
{
    byte[] buffer2;
    if (Logging.On)
    {
        Logging.Enter(Logging.Web, this, "DownloadData", address);
    }
    request = null;
    try
    {
        request = this.m_WebRequest = this.GetWebRequest(this.GetUri(address));
        buffer2 = this.DownloadBits(request, null, null, null);
    }
    catch (Exception exception)
    {
        if (((exception is ThreadAbortException) || (exception is StackOverflowException)) || (exception is OutOfMemoryException))
        {
            throw;
        }
        if (!(exception is WebException) && !(exception is SecurityException))
        {
            exception = new WebException(SR.GetString("net_webclient"), exception);
        }
        AbortRequest(request);
        throw exception;
    }
    catch
    {
        Exception exception2 = new WebException(SR.GetString("net_webclient"), new Exception(SR.GetString("net_nonClsCompliantException")));
        AbortRequest(request);
        throw exception2;
    }
    return buffer2;
}

score 0 · Answer 2 · answered Nov 01 '10 at 15:56

0

You could try calling GC.Collect to force the GC to run, seems that it might be the problem your having

answered Nov 01 '10 at 15:56

Fredrik Leijon

2,792
18
20

This really should not make a difference for classes implementing `IDisposble`. – Pieter van Ginkel Nov 01 '10 at 16:00
IIRC when you run under load there can be scenarios where the gc isn't able to run as it's supposed to, so the solution can be to call Collect on you own. – Fredrik Leijon Nov 01 '10 at 16:03
Component (base class of WebClient) already calls GC.Collect. If you use Reflector you can see that. – Aliostad Nov 01 '10 at 16:05

score 0 · Answer 3 · answered Nov 01 '10 at 16:03

0

You could try using HttpWebRequest instead of WebClient. In my experience, I usually have an easier time doing what I want with that API, though using it isn't quite as easy. I believe you can control connections a lot easier with HttpWebRequest.

answered Nov 01 '10 at 16:03

Jacob

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24
149
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WebClient in .Net not releasing socket resources

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