TryCatchFinally.net Some SQL, some .NET, and whatever else

15Jun/100

Periodic timeouts with local WCF endpoint

I have two applications - a Windows service and a client WinForm - that run on the same box, and the client needs to check on the status of the service every few seconds. It worked well most of the time, but every 4-5 times, it would timeout - I'd receive a System.TimeoutException, no matter how long the timeout was actually set for. It didn't make sense - the two apps are on the same box, it happens with both a TCP and an NamedPipe endpoint, and it can happen even when the service isn't busy.

It turns out that WCF endpoints only handle a very limited number of simultanious connections, and though I was creating a new ChannelFactory each time, I wasn't closing the channel when I was finished with it. I assumed that it would automatically close the channel when it passed out of scope, but no dice. Since the channels remained open, it didn't take long to fill them all up, and then the app would appear to be unresponsive until my channels started to time out. So here's what I ended up doing - critical line in bold, at the end:

Dim tcpBinding As New NetTcpBinding
Dim pipeFactory As ChannelFactory(Of WCF_Class.IServiceRemoting) = New  _
    ChannelFactory(Of WCF_Class.IServiceRemoting)(tcpBinding, "net.tcp://localhost:4079")
Dim ServiceWCFConnection As WCF_Class.IServiceRemoting = pipeFactory.CreateChannel
MessageBox.Show(ServiceWCFConnection.Responsive)
pipeFactory.Close() ' This is what's important!

That's it - make sure you close your Channel when you're done with it! If you leave it open, you quickly hit the server's connection limit and new requests will fail. Closing the channel when you're done frees it up, instead of letting it time out and close on its own.

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