How do I prevent a WCF service from enter a faulted state?


I have a WCF Service that should not enter the faulted state. If there's an exception, it should be logged and the service should continue uninterrupted. The service has a one-way operation contract and is reading messages from an MSMQ.

My problems are twofold:

  1. The service appears to be swallowing an exception/fault so I am unable to debug it. How do I get the service to expose the exception so that I can log or handle it?
  2. The service is entering into a faulted state after this exception is swallowed. How do I prevent the service from entering into a faulted state?
11/24/2008 10:31:33 PM

Accepted Answer

Most, if not all exceptions can be seen in the WCF Trace (Configuring Tracing) and the trace is best viewed with the Service Trace Viewer.

Obviously, this is not something you should have running all day in a production environment, but it helps in troubleshooting anyway.

Apart from that, note that oneways may not run as a true "fire and forget" depending on the SessionMode you use. If you have your service configured for SessionMode.Allowed or even SessionMode.Required, the oneway operation will run as if it was not oneway at all (this can be observed when using oneways over the netTcpBinding). To be frank, however, I don't know if that changes the type of exceptions you can get, or when you get them. However, in any case, you should get an exception if the request could not be send at all. AFAIK, the oneway "ends" when it is successfully enqued on the server side. So there is some place for (WCF framework related) exceptions until then (serialization/deserialization comes to mind).

Then, such framework related exceptions are best seen (even an IErrorHandler doesn't get them all due to the fact when it is called in the request/response-flow) using the above mentioned trace / traceviewer.

11/25/2008 6:54:29 AM

Exper Answer

Exceptions will fault the proxy. You can't AFAIK do much about that: don't cause exceptions ;-p

I'm a little surprised that one-way is still causing a problem, but for swallowing in general, there are 3 aspects:

  1. are you throwing faults? or exceptions? it matters (and should be "faults")
  2. as a hack, you can enable debug exception messages - but turn it off please!!!
  3. are you "using" the service object? I've just blogged on this exact subject... basically, your "using" can swallow the exception. 3 options:

    • don't use "using"
    • subclass the proxy and override Dispose()
    • wrap it, as per the blog
11/24/2008 10:46:28 PM

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