Why do my WCF service returning a FaultException, time out after 10 calls?

Question

I have a WCF service that sometimes has to return a Fault. For some reason, the calls to my service begins to time out with the following error: "The request channel timed out while waiting for a reply after 00:00:59.8906201. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout."

After examining the problem, a pattern emerged: When the service had returned a fault 10 times, the timeout starts. So I created a testservice implemented by:

public string GetData(int value)
{
    throw new FaultException("A testerror occured");
}

And a testclient:

   protected void RunTestGetData()
    {
        using (TestServiceReference.Service1Client client
            = new WSPerformanceTester.TestServiceReference.Service1Client())
        {
            try
            {
                client.GetData(1);
                client.Close();
                outputWriter.WriteLine(string.Format("Call run in thread {0}: GetData()", Thread.CurrentThread.ManagedThreadId));
                outputWriter.Flush();
            }
            catch (Exception e)
            {
                client.Abort();
                client.Close();
                outputWriter.WriteLine(string.Format("Error occured in thread {0}: GetData(): {1}", Thread.CurrentThread.ManagedThreadId, e.Message));
                outputWriter.Flush();
            }
        }
    }

This only happens, when the service is returning a FaultException. If I throw a normal exception, the service is able to continue running after the 10th call. Obviously, i would like to wrap my exceptions nicely, so just throwing normal exceptions is not a real option.

Why do I experience these timeout exceptions? Thanks in advance for any help..

Answer 1

I don't have enough points to comment, so new response...

Self hosted services only allow a max of 10 concurrent connections - no matter the transport. If you're running WCF services inside of IIS/WAS you shouldn't have to worry about this (unless you're on XP/Vista where the max concurrent connections is also 10).

Differences between a fault exception and a regular exception in this scenario can account for the result you're seeing.

Remember, a regular unhandled exception will fault the channel. In doing so I assume this opens up an available connection. When you return a fault, it won' automatically fault the channel because it allows you to do something with the connection and handle the fault on your end because it is a possible "expected" fault whereas an unhandled exception would not be.

Even when you return a fault, you still need to Abort() the connection. Also, underneath there are unmanaged resources so be sure to implement IDisposable on your clients/proxy's callers.

Answer 2

I think this might be because the default behavior of a WCF service is 10 concurrent sessions. Are you keeping the connections open after the FaultExceptions occur? You can try to alter this value in the BehaviorConfiguration (ServiceThrottling > MaxConcurrentSessions) and see if that changes anything. I suggest you use the Microsof Service Configuration Editor to check out what other values are set by default. (MSDN)

hope this helps...