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.
Related
I have a WCF Web Service that has no concurrency configuration in the web.config, so I believe it is running as the default as persession. In the service, it uses a COBOL Virtual Machine to execute code that pulls data from COBOL Vision files. Per the developer of the COBOL VM, it is a singleton.
When more than one person accesses the service at a time, I'll get periodic crashes of the web service. What I believe is happening is that as one process is executing another separate process comes in at about the same time. The first process ends and closes the VM down through normal closing procedures. The second process is still executing and attempting to read/write data, but the VM was shutdown and it crashes. In the constructor for the web service, an instance of the VM is created and when a series of methods complete, the service is cleaned up and the VM closed out.
I have been reading up on Singleton concurrency in WCF web services and thinking I might need to switch to this instead. This way I can open the COBOL VM and keep it alive forever and eliminate my code shutting down the VM in my methods. The only data I need to share between requests is the status of the COBOL VM.
My alternative I'm thinking of is creating a server process that manages opening the VM and keeping it alive and allowing the web service to make read/write requests through that process instead.
Does this sound like the right path? I'm basically looking for a way to keep the Virtual Machine alive in a WCF web service situation and just keep executing code against it. The COBOL VM system sends me back locking information on the read/writes which I can use to handle retries or waits against.
Thanks,
Martin
The web service is now marked as:
[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single)]
From what I understand, this only allows a single thread to run through the web service at a time. Other requests are queued until the first completes. This was a quick fix that works in my situation because my web service doesn't require high concurrency. There are never more than a handful of requests coming in at a time.
I have an IIS hosted WCF service, and a client Windows application which, upon the first use of the day, takes a while to respond to the first service call. I believe this to be because IIS shuts down services which are not used for a period of time (and the delay is the restart time for the service). I was wondering whether I could alleviate this by making an asynch call when my application starts up (just to, potentially, get the service to start). I therefore, upon application start, created a "fire and forget" background thread which just opens a connection to the service. The intention being that when my application has finished its own startup, and wants to use the WCF service, the thread will (probably) have finished and the service startup delay will not be encountered by the user.
Is this reasonable ? Is opening a channel to the WCF service enough, on its own, to start the service, or do I need to write some dummy method and call that ?
Thanks
Ross
Check if you really want your app to handle this task and checkout the AppWarm-Up Module for IIS, maybe you can use this without adding code to your serivce.
Is this reasonable ?
It doesn't sound like a good approach to me. If you have control over how the service is hosted I would advise you to self-host it.
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'm curious to know how I would go about setting up my service to stop cleanly on the server the service will be installed on. For example when I have many clients connecting and doing operations every minute and I want to shut-down the service for maintenance, how can I do this in the "OnStop" event of the service to then let the main service host to deny any new client connections and let the current connections finish before it actually shuts down its services to the client, this will ensure data isn't corrupted on the server as the server shuts down.
Right now I'm not setup as a singleton because I need scalability in the service. So I would have to somehow get my service host to do this independently of knowing how many instances are created of the service class.
You just have to call Dispose on the ServiceHost instance that you create. Once you do that, you will not accept any more clients and the service will continue to finish the operations for clients that are already connected.
I've been wondering the same thing. I found this article which has a pretty in-depth description of how to properly Close/Dispose as ServiceHost or Client.
http://www.danrigsby.com/blog/index.php/2008/02/26/dont-wrap-wcf-service-hosts-or-clients-in-a-using-statement/
In order to accomplish this. I had to create a service reference of itself and in the Windows Service OnStop initiate a new connection and change values in the WCF Service to "shut down" (this was just a shared boolean that the service was online or offline) the service so new clients wouldn't be able to connect (A function the client would call to see if the server was online or offline) and the existing connections would have time to finish up, then after all clients disconnect, continue to shut down the WCF Service using the .Close method.
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.