Is it possible to run multiple instances of the same XPC service using the XPC APIs found in Foundation.framework (NSXPCConnection, etc.)? The docs don't provide much insight on this matter.
EDIT: Did a quick test, and it seems like only one instance of the service is running even though I created two XPC connections. Is there any way to have it run another instance?
A bit late, but the definitive answer to this question is provided in the xpcservice.plist manpage:
ServiceType (default: Application)
The type of the XPC Service specifies how the service is instantiated.
The values are:
• Application: Each application will have a unique instance of this service.
• User: There is one instance of the service process created for each user.
• System: There is one instance of the service process for the whole system. System XPC Services are restricted to reside in system frameworks and must be owned by root.
Bottom line: In most cases there is a single instance of an XPC Service and only in the case where different applications can connect to the same service (not even possible when the service is bundled with an app), will there be multiple instances (one-instance-per-app).
I believe XPC services designed for one instance per multiple connections. Probably, it is more convenient to manage named pipes with one running executable. So, the most likely it is impossible to create multiple instances simultaneously.
Since XPC services should have no state, it should not matter, whether one ore more instances are running:
XPC services are managed by launchd, which launches them on demand, restarts them if they crash, and terminates them (by sending SIGKILL) when they are idle. This is transparent to the application using the service, except for the case of a service that crashes while processing a message that requires a response. In that case, the application can see that its XPC connection has become invalid until the service is restarted by launchd. Because an XPC service can be terminated suddenly at any time, it must be designed to hold on to minimal state—ideally, your service should be completely stateless, although this is not always possible.
–– Creating XPC Services
Put all neccessary state information into the xpc call and deliver it back to the client, if it has to persist.
https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man5/xpcservice.plist.5.html
ServiceType key in XPCService dictionary: Application or User or System
But this ‘ServiceType’ is irrelevant… IF Service is embedded in an application bundle then it will only be visible to the containing application and will be, by definition, Applicaton-type services. A subsequent connection request from an application to a service will result in a new connection to an existing service.
I know I'm late to the party, but while you can't do this with plain XPC,
there's library (a component of OpenEmu) that should be able to do what you're asking: OpenEmuXPCCommunicator
Related
i can't find any good architecture explanation of how can WCF SHOULD be part of a main-server with multiple clients.
in my solution, i want to have a central WCF service (hosted in windows-service on windows server machine).
The central service is the only one that's connected to the DB.
all the clients, are connecting to this main service, login, and get having a duplex communication.
via that main service, one client can connect another one. or when one client using the main service to change the DB, the main service updates all other clients.
for doing that, i added in the main service the InstanceContextMode.Single attribute, and in the windows-service, i init ServiceHost with the WCF-service singleton.
it works. so so..
i can continue and search where the problems are, and how to fix them, but it looks like something here is not right, like i'm not supposed to do it this way.
i could really use an advice on how WCF service should be used as a main service with multiple clients, that require common memory.
it's basically for ~20 clients with not too intensive operations, but i still want the option to let them all communicate simultaneously with the main service, and not only one by one.
I'm writing an application which will use the Azure Service Bus. For local development I'm using Windows Server Service Bus to provide the same services (the code to use either is identical).
I want to write the application to be tolerant of transient errors when sending or receiving messages. To that end, I want to be able to test the fault-handling code can deal with the local Service Bus instance suddenly being unavailable during execution of various operations.
Ideally, I'd want to write some automated integration tests around these scenarios, but I appreciate that may not be practically achieved.
What can I do to simulate transient errors on my local Service Bus?
One easy thing would be to call the stop-sbservice (affects one node) or stop-sbfarm (affects the entire farm) cmdlets. This would let you simulate a servicebus outage locally. You can then call start-sbservice or start-sbfarm to bring the service back and validate that your code recovers properly. This approach also has the added benefit that you control when the service returns (compare to just crashing the process). This page has information on the available cmdlets.
If that's not enough, another approach that I've used in the past is to shut down the network interface, or, if the server is in another machine, put up a firewall on the ports used to communicate to service bus.
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.
Have a winform application and want to host a WCF service inside it. Do I need to host it in a seperate appdomain? Any recommendations?
You don't need to host it in separate domain but you must decide if you want service request to be processed by UI thread or different thread. It depends on the way you create ServiceHost instance or on ServiceBehavior applied to your service class.
When service is hosted in UI thread it can directly interact with UI but request processing is part of message loop and all service requests are processed by single thread (sequentially). When request is processed no other windows event (including UI events) can be processed = application freezes.
When service is hosted in different thread it behaves as in any other hosting environment but it can't directly interact with UI - you must use delegate invocation.
Ways to enforce service to run in own threads:
Create and open ServiceHost instance before you call Application.Run (start of Windows message loop)
Create and open ServiceHost instance in separate thread
Use [ServiceBehavior(UseSynchronizationContext = false)] on your service implementation
No, you don't have to host it in a separate AppDomain. Just host it. There's nothing terribly special about WinForms in this regard.
What's your app do? Is the service a part of the apps regular functions or a completly seperate logical entity?
If you want to be loading and unload resources (such as assemblies) related to your service without shutting your app down a seperate app domain would make this much easier, but otherwise I don't see much of a reason to complicate things.
Just my 2c. :-)
You can host in Win form but you have to keep it running throughout.
Also suggest you to host in IIS so any type of client avail your service.
First of all i will describe current state:
Server consists of several WCF services, hosted in one or several win services on diffirent machines.
Service responsible for recieving data from diffirent devices. Communication with devices is implemented using sockets. Service instance mode - singleton.
Data broker service - responsible for persisting data and sharing in by request. Instance mode - singleton.
Configuration service - responsible for changing configuration database and working with administration console(WPF app, like SSMS). Handles connections from console, subscriber management, etc. Instance mode - singleton.
Client access service - quite the same as above thith management of clients but also notifyes clients of new data, and acts like facade to service bus. And singleton again.
Identity management service - Checks permissions and returns result. Singleton.
All of those services are connected with NServiceBus and i realy like how it works at this moment.
But:
Too many singletons. Mainly because to use servicebus i must have single instance of it afaik. I dunno maybe i can use nservice bus in session mode, but dont know how to handle issue that all of those services will use one queue.
And what if i will have 300+ clients? singleton can become unresponsive..
And i wanted to ask for some critics about all of this and maybe some one could suggest something.
Thanks in advance.
Alexey
Alexey,
While you should only have one instance of the bus per process, you can put that instance in a globally accessible place (as shown in the AsyncPages sample), and use that from non-singleton objects like web pages and WCF services.
Also, it is probably not appropriate to have all your services using one queue. Without better understanding your situation, I'd give the default recommendation of one queue for each of the services you identified.
Hope that helps.