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POWhat is the best workaround for the WCF client `using` block issue?
 

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  1. POWhat is the best workaround for the WCF client `using` block issue?
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    <p>I like instantiating my WCF service clients within a <code>using</code> block as it's pretty much the standard way to use resources that implement <code>IDisposable</code>:</p> <pre><code>using (var client = new SomeWCFServiceClient()) { //Do something with the client } </code></pre> <p>But, as noted in <a href="http://msdn.microsoft.com/en-us/library/aa355056.aspx" rel="noreferrer">this MSDN article</a>, wrapping a WCF client in a <code>using</code> block could mask any errors that result in the client being left in a faulted state (like a timeout or communication problem). Long story short, when Dispose() is called, the client's Close() method fires, but throws an error because it's in a faulted state. The original exception is then masked by the second exception. Not good.</p> <p>The suggested workaround in the MSDN article is to completely avoid using a <code>using</code> block, and to instead instantiate your clients and use them something like this:</p> <pre><code>try { ... client.Close(); } catch (CommunicationException e) { ... client.Abort(); } catch (TimeoutException e) { ... client.Abort(); } catch (Exception e) { ... client.Abort(); throw; } </code></pre> <p>Compared to the <code>using</code> block, I think that's ugly. And a lot of code to write each time you need a client.</p> <p>Luckily, I found a few other workarounds, such as this one on IServiceOriented. You start with:</p> <pre><code>public delegate void UseServiceDelegate&lt;T&gt;(T proxy); public static class Service&lt;T&gt; { public static ChannelFactory&lt;T&gt; _channelFactory = new ChannelFactory&lt;T&gt;(""); public static void Use(UseServiceDelegate&lt;T&gt; codeBlock) { IClientChannel proxy = (IClientChannel)_channelFactory.CreateChannel(); bool success = false; try { codeBlock((T)proxy); proxy.Close(); success = true; } finally { if (!success) { proxy.Abort(); } } } } </code></pre> <p>Which then allows:</p> <pre><code>Service&lt;IOrderService&gt;.Use(orderService =&gt; { orderService.PlaceOrder(request); }); </code></pre> <p>That's not bad, but I don't think it's as expressive and easily understandable as the <code>using</code> block.</p> <p>The workaround I'm currently trying to use I first read about on <a href="http://blog.davidbarrett.net/archive/2007/11.aspx" rel="noreferrer">blog.davidbarret.net</a>. Basically you override the client's <code>Dispose()</code> method wherever you use it. Something like:</p> <pre><code>public partial class SomeWCFServiceClient : IDisposable { void IDisposable.Dispose() { if (this.State == CommunicationState.Faulted) { this.Abort(); } else { this.Close(); } } } </code></pre> <p>This appears to be able to allow the <code>using</code> block again without the danger of masking a faulted state exception. </p> <p>So, are there any other gotchas I have to look out for using these workarounds? Has anybody come up with anything better?</p>
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    1. COThe last one (which inspects this.State) is a race; it might not be faulted when you check the boolean, but might be faulted when you call Close().
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    2. COYou read state; it's not faulted. Before you call Close(), the channel faults. Close() throws. Game over.
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    3. COTime passes. It may be a very short period of time, but technically, in the time period between checking the state of the channel and asking it to close, the channel's state may change.
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