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PODns.BeginGetHost... methods blocking
 

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    <p>So I want to make a <strong>lot</strong> of DNS queries.</p> <p>I create (thousands) of Tasks from the <code>Begin/EndGetHostEntry</code> async pair:</p> <pre><code>var lookupTask = Task.Factory.FromAsync ( Dns.BeginGetHostEntry, (Func&lt;IAsyncResult, IPHostEntry&gt;) Dns.EndGetHostEntry, "google.com", null ) </code></pre> <p>then <code>Task.WaitAll</code> for everything to complete. I'm seeing the number of <code>ThreadPool</code> threads increase drastically in response to my requests. If I force the <code>ThreadPool</code> <code>minThreads</code> to 500, the workload is consumed considerably faster. All of this points to blocking in the <code>Dns</code> asynchronous implementation.</p> <p>If I replace <code>Dns</code> with a <a href="http://arsofttoolsnet.codeplex.com/">managed Dns client</a>, I can consume the same workload with only 1 or 2 threads in the <code>ThreadPool</code> with cpu virtually idling.</p> <p>The thing is, the <code>Dns</code> implementation is absolutely core to many networking APIs (<code>HttpWebRequest</code>, <code>WebClient</code>, <code>HttpClient</code>), and they all seem to be affected by this issue. If I resolve DNS with a 3rd party library, and make HTTP requests using the IP address as the host in the uri, then alter the <code>Host</code> header to fix the request, I get blistering performance in comparison to anything involving <code>System.Net.Dns</code>.</p> <p>What's going on here? Have I missed something or is the <code>System.Net.Dns</code> implementation really that bad?</p>
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    1. COI've never had someone else offer their rep for bounty on my question. Nice!
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    2. COI thought it would be interesting. I know that there's also [`GetHostAddresses`](http://msdn.microsoft.com/en-us/library/system.net.dns.gethostaddresses) but it has a limit of 255 characters, which might limit the batching effect enough to not be an alternative. There's also [a Task async method in .NET 4.5](http://msdn.microsoft.com/en-us/library/hh194304) but there's no further notes on how it performs.
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    3. COAh. They hadn't added a async versions when I originally posted... interesting... decompiler session ahead.
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