I'm developing a client/server app in which the client calls the WCF service every few seconds. I'm not using IIS - the service runs as a console app (with the intention of installing it as a Windows service on production systems).
I started off using basicHttpBinding, and if I stop the service (to simulate a comms/server failure) the client simply ignores the fact that it can't connect to the service, by handling the EndpointNotFoundException that gets thrown. After restarting the service, the client is able to start calling it again and everything is good.
I've now switched to using netTcpBinding, and this time when I stop the service it takes a little while for its console window to close (presumably due to the way TCP manages the connection, which eventually times out). At this point the client gets a CommunicationException ("the socket connection was aborted"). When I restart the service, the client isn't able to "resume" like it did with basicHttpBinding. Each time it tries to call the service it throws a CommunicationObjectFaultedException ("The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.").
How would I go about building in some kind of resume/recovery behaviour, similar to what I saw with basicHttpBinding?
You cannot reuse the channel as it has faulted. You should cast your client to an ICommunicationObject and call Abort() to clean up.
After that you simply start afresh by creating a new client channel. You may want to do this on a timer if your server is down for a period of time.
Related
Good time of day. I would like to know how to properly connect in a WCF application. In other words, it should be created when the app is launched and be active throughout the entire operation? Or do you need to create a connection every time a service function is called? Now I have the first option, but somewhere everything is fine, and sometimes for unknown reasons I get an error: it is Impossible to use the object for communication, since it is in the failed state. There are no visible reasons for this - the code runs without errors. NetTcpBinding is used as the binding
The wcf service needs to be hosted in the process so that the client can connect to the server. As long as you are using the wcf service, you need to enable it. Faulted state means there has been an unexpected exception on the server side, so you need to use a try…catch block. Another possibility is that the channel has expired. The default timeout period of the WCF service is 10 minutes. If the client does not communicate with the server within 10 minutes, the channel will be closed. You need to recreate the channel to call the service.
I am using NetNamedPipebinding to communicate between two processes. One of them provides a service at an end point and the other process using DuplexChannel communicates with it.
In some scenario my client process might crash. In those scenarios I need to kill the service process as well. What is the best way to achieve it?
From server side:
I am thinking of having a timer and call the ping method on the callback. If client doesn't respond for ping, I can shut down the service as well. Is there any better solutions?
I am the one who creates the service (process). So I simply passed the process ID of the client process to server (service process) and listen to Process.Exited event.
I have two windows services. One ('server') acts as a WCF host to which the other ('client') connects. So I have configured a dependency from client to server. Both are also set up to start automatically.
When I start these services by hand, everything works fine. When I stop both services and tell client to start, then server will be started before client and all is fine.
However, when I reboot the machine only server is started.
When I add a diagnostic listener I see it got a TimeoutException with the helpful message:
The HTTP request to 'http://[server address]' has exceeded the allotted timeout of 00:00:00. The time allotted to this operation may have been a portion of a longer timeout.
At some other SO question there was an answer that claims WCF is probably confused about what went wrong and therefore starts lying about the timeout.
Did I perhaps miss a dependency for either service? Does WCF require something that hasn't or is being started when client is trying to contact server?
I think you should check your client service. On startup windows services are starting while network devices are still being initialized. Services should be ready to start without network and without any network device. Usual approach is to keep periodic retries to establish connection. You can do little experiment on your machine by uninstalling all network adapters and trying to start up your services.
Additional quick workaround you can do is to setup recovery options on your service -- for example you can configure it to restart service on crash after some timeout -- you can do this through UI in services.msc or in command line using 'sc config' command.
Configuring the dependency between the two Windows Services is not necessarily sufficient to avoid there being a race condition: i.e. to avoid the client service calling the WCF service before the server's WCF channel stack is fully initialised.
The service dependency just ensures that the Windows Service Control Manager won't start the client service process before the server Windows Service has notified the SCM that it has started. Whether this is sufficient depends on how you write the server.
If the server service starts a new thread on which to initialize the WCF stack, your OnStart method is probably returning before the WCF stack is ready for clients. There is then a race condition as to whether the client's first call will succeed.
On the other hand, if the server service does not return from OnStart (and thus doesn't notify the SCM that it has started) until the channel stack is fully open, the dependency removes the race condition, but there is a different pitfall: you need to beware that the SCM's own timeout for starting the Windows service is not triggered while waiting for the WCF stack to initialise, as might well happen on a reboot if the WCF service depends on the network stack, for example. If the server's OnStart does not return within the SCM's timeout, the SCM will not try to start the dependent client service at all, because it does not receive the server's start notification. (There will be a message in the Windows event log from the SCM saying that the server service didn't start within the expected time.) You can extend the SCM timeout by calling ServiceBase.RequestAdditionalTime while the WCF service is being initialised.
Either way, the client service really ought to be written so that it doesn't fail completely if the first WCF call doesn't succeed.
You don't actually say what binding you are using. If client and server services are always running on the same machine, as you seem to indicate, then consider using the NetNamedPipeBinding: then your service won't be dependent on initialization of networking resources and startup should be quicker.
I have 2 wcf services, 1 which polls the other service at regular interval.The service2 is hosted in no. of machines with the same configuration.
My problem is that whenever the poller service gets restarted, even though the service2 on other machines runs fine, i am not getting the response from those services (basically it gets timed out - getting SYSTEM.TimeOutException ). If I try to access the same service (service2) from some temp application (without restarting the service2) it gives response.
If I restart the service2, than it works fine, the service1 (poller service) gets the responses from all hosted services (Service2).
Dont know what is causing problem.
Regards,
Chirag
Attach VS to your wcf service which hangs. And find out if your connection is successful.
Do it with both services, so that you can debug the services at runtime.
If you're using a sessionful binding (netTcpBinding, wsHttpBinding), it's more than likely that you're not explicitly closing your client channel when you're done with it. This would cause the behavior you see, because the session takes a minute or so to time out if you don't explicitly close it, and the default max number of sessions is low (10)- the server will let new sessions stack up until old ones close. You can also adjust the service throttle on the server side binding to increase the max number of open sessions allowed, but you really should make sure your clients are getting cleaned up properly first.
I have a WCF Service that I have written, which is hosted within a Windows service. It is operating in PerSession mode. The service permits clients to open files, make changes to files and close files remotely through the service. So far all works very smoothly.
When the Windows service is stopped, I would like to be able have the WCF Service not accept any new sessions and yet allow already connected clients to complete their current sessions and work (within a reasonable period/timeout).
What would be the best way to accomplish this?
Basically, calling ServiceHost.Close() will accomplish this - it will let all currently running request run to completion, but new request are being rejected will the orderly shutdown is in progress.
There's a "CloseTimeout" setting on your binding that you configured for your service - that controls how long the WCF runtime will allow running requests to take until they've properly shut down. If that timeout happens, the still running requests will be killed.
The ServiceHost.Abort() method on the other hand is the digital equivalent of a sledgehammer - all running requests are terminated at once, and the host is shut down.
ON the client side, you have the same .Close() and .Abort() methods on your client proxy which behave the same way.