I'm looking for a way to cache objects in memory with a RESTful WCF service. The service is completely stateless and is hosted outside of an IIS. I want to implement the caching by myself, so memcached isn't an option.
Right now I'm thinking of hosting a separate stateful System.ServiceModel.ServiceHost that does all the caching. It'll communicate with the rest of the WCF methods through a separate port or by some other means. However I'm not sure if this is the ideal solution to my problem. Has anyone got any tips?
I understand your confusion between stateless service and a stateful host and how the two can interact.
In this code sample I demonstrate conceptually how an in-memory singleton (Caching mechanism, I refer to as CachingProvider henceforth) can be referenced by both the service class (the service instance more precisely during the lifecycle of the request) and the service host (in this case I chose it to be a Console Application)
I assume here, the service interface and class are both located within the console applicaiton project that hosts the service.
In this simple example, my primitive CachingProvider class basically acts as a counter of how many service calls are made to the GetData method, and the service host will poll the CachingProvider every 5 seconds to get the count of service calls made so far.
note: you can use the WCFTestClient utility to test this quickly.
Disclaimer: I by no means suggest that a complex Caching mechanism be implemented as simply as in this sample, this code is merely for demosntration purposes.
namespace ServiceHostConsole
{
[ServiceContract]
public interface ITestService
{
[OperationContract]
string GetData(int value);
}
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class TestService : ITestService
{
public TestService()
{
CachingProvider.CallCount++;
}
public string GetData(int value)
{
return string.Format("You entered: {0}", value);
}
}
//For demonstration purposes only
static class CachingProvider
{
static CachingProvider()
{
//private static constructor can initialize
//static cacheable resources
_callCounter = 0; //Trivial example of initialization
}
private static int _callCounter;
public static int CallCount
{
set { _callCounter = value; }
get { return _callCounter; }
}
}
class Program
{
static void Main()
{
using (var host = new ServiceHost(typeof(TestService), new Uri("http://localhost/TestService")))
{
host.Open();
//Example how the ServiceHost can report on a persistent in-memory object that is being
//updated each time the service is called.
new Timer(state => Console.WriteLine("# of service calls: {0}", CachingProvider.CallCount), null, 0, 5000);
Console.Read();
host.Close();
}
}
}
}
Related
I have a simple service interface I am using to synchronize data with a server via HTTP. The service interface has a method to start and stop the synchronization process. The idea is to start the synchronization process after the user signs in, and stop the synchronization at the end of the application before the user signs out. The synchronization service will check for new messages every few minutes, and then notify the ViewModel(s) of new/changed data using the MvxMessenger plugin.
What is the recommended way to ensure the synchronization service lives for the duration of the app? I am currently using a custom IMvxAppStart which registers the service interface as a singleton, and then holds a static reference to the service interface. Is that enough to keep the service alive for the lifetime of the app, or is there a better way?
public class App : MvxApplication
{
public override void Initialize()
{
...
RegisterAppStart(new CustomAppStart());
}
}
public class CustomAppStart : MvxNavigatingObject, IMvxAppStart
{
public static ISyncClient SynchronizationClient { get; set; }
public void Start(object hint = null)
{
SynchronizationClient = Mvx.Resolve<ISyncClient>();
ShowViewModel<SignInViewModel>();
}
}
public interface ISyncClient
{
void StartSync();
void StopSync();
bool IsSyncActive { get; }
}
You don't need a static property for this. When you register the Interface as a singleton, the IoC do the work for you. Example: In one of our apps wee need a state-property with important data for the whole lifetime of the app.
The models who need this state, just uses following code snippet:
protected IApplicationState AppState
{
get { return _appstate ?? (_appstate = Mvx.GetSingleton<IApplicationState>()); }
}
private IApplicationState _appstate;
But: You can do it also with a static property. But in this case you don't need a singleton-value in the IoC.
I have the following simple WCF library which was developed on Visual Studio 2008.
When running WCFTestClinet/javascript(with SOAP) that calls this wcf service I get false value for the following scenario:
1. GetNumber --> output: "Your number is 0"
2. SetNumber --> No output
3. GetNumber --> output: "Your number is 0" instead of output: "Your number is 8" !!!
Can anyone explain why is this happening and how can I solve it?
Thanks
public class Service1 : IService1
{
private int Number;
public string GetData(int value)
{
return string.Format("You entered: {0}", value);
}
public CompositeType GetDataUsingDataContract(CompositeType composite)
{
if (composite.BoolValue)
{
composite.StringValue += "Suffix";
}
return composite;
}
public string GetNumber()
{
return string.Format("Your number is : {0}", Number);
}
public void SetNumber()
{
Number = 8;
}
}
It's all about instances. One instance of your service will by default be instantiated per session; but depending on the configuration (for example using the BasicHttpBinding) the service may be instantiated per call (and/or not even support sessions at all).
Probably because you have configured your WCF service to be per call instead of per session.
Great answer telling the differences: https://stackoverflow.com/a/2542991/70386
How per call works: http://wcftutorial.net/Per-Call-Service.aspx
Per session: http://wcftutorial.net/Per-Session-Service.aspx
Is this in the same instance? As Number will always be set to 0 otherwise
I haven't used the SOAP WCF, but in my work with other web services my understanding is that each time an invocation is made to the service a new instance is created. This means that whatever you did on SetNumber is not there for the following GetNumber as it is a new instance.
If you wanted, you could make that value static to preserve the changes between calls.
This is because by default, WCF 3.5's instance mode is PerCall. This means that for every call WCF receives, it creates a new instance of the service class, performs the call, and then destroys that instance.
If you want to have shared values you can configure your service to be a singleton, like so:
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class Service1 : IService1
I have a Client Application, a server and another client, lets call it third party. I have a callback interface as part of my contract that is implemented both by the third party and the client.
The third party will call a server operation(method) then the server will trigger a callback but instead of calling the callback of the third party, it will call the callback implementation of the client.
Yes, you can absolutely do that.
The easiest way is to implement your service as a PerSession service, and capture the callback context on initialization/construction. Typically I will add the service object (which really represents a connection at that point) to an internal core object.
Then, when you get in a message from a client, you can make a call to any of the service objects (not through the contract), and internally forward the data to the associated client.
This is a pretty minimal implementation of the concept, without exception handling, and some pretty bad design (static class BAD!). I haven't tested this, but the principles should hold even if I missed crossing an i or dotting a t. This example also forwards the calls to all clients, but selecting an individual client follows the same basic pattern.
Trying to do this with a singleton service will be more difficult, and a per-call service obviously won't work :)
[ServiceContract(CallbackContract = typeof(ICallback))]
public interface IContract
{
[OperationContract(IsOneWay = true)]
void SendTheData(string s);
}
public interface ICallback
{
[OperationContract(IsOneWay = true)]
void ForwardTheData(string s);
}
[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant, InstanceContextMode = InstanceContextMode.PerSession)]
public class ServiceConnection : IContract
{
private ICallback m_callback;
public ServiceConnection()
{
m_callback = OperationContext.Current.GetCallbackChannel<ICallback>();
ServiceCore.Add(this);
}
public void SendTheData(string s)
{
ServiceCore.DataArrived(s);
}
public void SendToClient(string s)
{
m_callback.ForwardTheData(s);
}
}
static public class ServiceCore
{
static private List<ServiceConnection> m_connections = new List<ServiceConnection>();
public static void DataArrived(string s)
{
foreach(ServiceConnection conn in m_connections)
{
conn.SendTheData(s);
}
}
public static void Add(ServiceConnection connection)
{
m_connections.Add(connection);
}
}
From a quick read of the Microsoft Duplex service documentation I don't think that will do what you want. There could be some other clever Kung Fu WCF way to do it but in my case I created a "PassThruService" for the server that implemented the same contract as the real service and sent any requests received onto the client.
This is a part of my code that explains the thrust of it.
private const int OPERATION_TIMEOUT = 5000;
private MyServiceClient m_client = new MyServiceClient();
public bool IsAlive() {
try {
logger.Debug("PassThruService IsAlive.");
bool isAlive = false;
ManualResetEvent isAliveMRE = new ManualResetEvent(false);
m_client.IsAliveComplete += (s, a) => { isAlive = a.Result; isAliveMRE.Set(); };
m_client.IsAliveAsync();
if (isAliveMRE.WaitOne(OPERATION_TIMEOUT)) {
return isAlive;
}
else {
throw new TimeoutException();
}
}
catch (Exception excp) {
logger.Error("Exception PassThruService IsAlive. " + excp.Message);
throw;
}
I don't fully see what you're really asking here.... but I'll try to give some tips anyway.
Relaying messages or routing is not very well supported in WCF in .NET 3.5 - the infrastructure is there, but it's still a lot of work to set it up manually.
The best intro I know into this topic for WCF in .NET 3.5 is a two-part article by Michele Leroux Bustamante on MSDN magazine:
Building a WCF Router, Part 1
Building a WCF Router, Part 2
Part 2 has a section on duplex routers - does that help you in your quest at all??
WCF in .NET 4.0 promises to bring additional support for routing - there will be a RoutingService base class which can be leveraged to write routing services, and it will allow for configurable, content- or metadata-based routing - whatever it is that you need.
.NET 4.0 is scheduled to be released sometime later this year (2009) - hopefully! So while this is still the future, it's looking rosy!
Marc
I think I found the solution..
Here's the link.
http://msdn.microsoft.com/en-us/magazine/cc163537.aspx
Try to look at figure 6. That's what I'm trying to achieve.
Context:
I need to develop a monitoring server that monitors some of our applications (these applications are in c#). So I decided to develop the system with WCF which seems suitable for my needs.
These applications must register themselves to the monitoring server when they start. After that the monitoring server can call the methods Start or Stop of these applications.
Everything is completely executed on the same machine, nothing needs to be executed remotely.
So I developed a good prototype and everything works fine. Each application registers itself to the monitoring server.
Question:
ApplicationRegistrationService (see the code below) is the implementation of the monitoring service and it is a singleton instance due to the ServiceBehavior attribute.
Here my problem: I want to access the content of ApplicationRegistrationService per example, the number of connected applications from my server (ConsoleMonitoringServer in the example). But, I am not sure how to achieve this.
Do I need to create a channel in my server to the service like I did in my clients (ConsoleClient) or it exists a better way to achieve this?
Code:
The code is very simplified for the purpose of this question:
//The callback contract interface
public interface IApplicationAction
{
[OperationContract(IsOneWay = true)]
void Stop();
[OperationContract(IsOneWay = true)]
void Start();
}
[ServiceContract(SessionMode = SessionMode.Required,
CallbackContract = typeof(IApplicationAction))]
public interface IApplicationRegistration
{
[OperationContract]
void Register(Guid guid, string name);
[OperationContract]
void Unregister(Guid guid);
}
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single,
ConcurrencyMode = ConcurrencyMode.Multiple)]
public class ApplicationRegistrationService : IApplicationRegistration
{
//IApplicationRegistration Implementation
}
public class ApplicationAction : IApplicationAction
{
//IApplicationAction Implementation
}
Console application for this example
class ConsoleClient
{
static void Main(string[] args)
{
ApplicationAction actions = new ApplicationAction();
DuplexChannelFactory<IApplicationRegistration> appRegPipeFactory =
new DuplexChannelFactory<IApplicationRegistration>(actions,
new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/AppReg"));
IApplicationRegistration proxy = appRegPipeFactory.CreateChannel();
proxy.Register(Guid.Empty, "ThisClientName");
//Do stuffs
}
}
Console server for this example
class ConsoleMonitoringServer
{
static void Main(string[] args)
{
using (ServiceHost host = new ServiceHost(typeof(ApplicationRegistrationService),
new Uri[]{ new Uri("net.pipe://localhost")}))
{
host.AddServiceEndpoint(typeof(IApplicationRegistration),
new NetNamedPipeBinding(), "AppReg");
host.Open();
//Wait until some write something in the console
Console.ReadLine();
host.Close();
}
}
}
Finally, I find the answer and it was pretty easy. I just need to create the service instance and pass the reference to the constructor of ServiceHost.
So I need to replace the following code:
using (ServiceHost host = new ServiceHost(typeof(ApplicationRegistrationService),
new Uri[]{ new Uri("net.pipe://localhost")}))
by :
ApplicationRegistrationService myService = new ApplicationRegistrationService();
using (ServiceHost host = new ServiceHost(myService,
new Uri[]{ new Uri("net.pipe://localhost")}))
If you mean you'd like two way communication between your monitoring service and your registered services or nodes, then you probably should be using two way communication in WCF also known as duplex communication. Very cool stuff.
http://www.codeproject.com/KB/WCF/WCF_Duplex_UI_Threads.aspx
I am trying to migrate my .net remoting code to wcf but I'm finding it difficult. Can someone help me migrate this simple Remoting based program below to use WCF? The program implements a simple publisher/subscriber pattern where we have a single TemperatureProviderProgram that publishers to many TemperatureSubcriberPrograms that subcribe to the TemperatureProvider.
To run the programs:
Copy the TemperatureProviderProgram and TemperatureSubcriberProgram into seperate console application projects.
Copying to remaining classes and interfaces into a common Class Library project then add a reference to System.Runtime.Remoting library
Add a reference to the Class Library project from the console app projects.
Complie and run 1 TemperatureProviderProgram and multiple TemperatureSubcriberProgram.
Please note no IIS or xml should be used. Thanks in advance.
public interface ITemperatureProvider
{
void Subcribe(ObjRef temperatureSubcriber);
}
[Serializable]
public sealed class TemperatureProvider : MarshalByRefObject, ITemperatureProvider
{
private readonly List<ITemperatureSubcriber> _temperatureSubcribers = new List<ITemperatureSubcriber>();
private readonly Random randomTemperature = new Random();
public void Subcribe(ObjRef temperatureSubcriber)
{
ITemperatureSubcriber tempSubcriber = (ITemperatureSubcriber)RemotingServices.Unmarshal(temperatureSubcriber);
lock (_temperatureSubcribers)
{
_temperatureSubcribers.Add(tempSubcriber);
}
}
public void Start()
{
Console.WriteLine("TemperatureProvider started...");
BinaryServerFormatterSinkProvider provider = new BinaryServerFormatterSinkProvider();
provider.TypeFilterLevel = System.Runtime.Serialization.Formatters.TypeFilterLevel.Full;
TcpServerChannel tcpChannel = new TcpServerChannel("TemperatureProviderChannel", 5001, provider);
ChannelServices.RegisterChannel(tcpChannel, false);
RemotingServices.Marshal(this, "TemperatureProvider", typeof(ITemperatureProvider));
while (true)
{
double nextTemp = randomTemperature.NextDouble();
lock (_temperatureSubcribers)
{
foreach (var item in _temperatureSubcribers)
{
try
{
item.OnTemperature(nextTemp);
}
catch (SocketException)
{}
catch(RemotingException)
{}
}
}
Thread.Sleep(200);
}
}
}
public interface ITemperatureSubcriber
{
void OnTemperature(double temperature);
}
[Serializable]
public sealed class TemperatureSubcriber : MarshalByRefObject, ITemperatureSubcriber
{
private ObjRef _clientRef;
private readonly Random portGen = new Random();
public void OnTemperature(double temperature)
{
Console.WriteLine(temperature);
}
public override object InitializeLifetimeService()
{
return null;
}
public void Start()
{
BinaryServerFormatterSinkProvider provider = new BinaryServerFormatterSinkProvider();
provider.TypeFilterLevel = System.Runtime.Serialization.Formatters.TypeFilterLevel.Full;
int port = portGen.Next(1, 65535);
TcpServerChannel tcpChannel = new TcpServerChannel(string.Format("TemperatureSubcriber_{0}", Guid.NewGuid()), port, provider);
ChannelServices.RegisterChannel(tcpChannel, false);
ITemperatureProvider p1 = (ITemperatureProvider)RemotingServices.Connect(typeof(ITemperatureProvider), "tcp://localhost:5001/TemperatureProvider");
_clientRef = RemotingServices.Marshal(this, string.Format("TemperatureSubcriber_{0}_{1}.rem", Environment.MachineName, Guid.NewGuid()));
p1.Subcribe(_clientRef);
}
}
public class TemperatureProviderProgram
{
static void Main(string[] args)
{
TemperatureProvider tp = new TemperatureProvider();
tp.Start();
}
}
public class TemperatureSubcriberProgram
{
static void Main(string[] args)
{
Console.WriteLine("Press any key to start TemperatureSubcriber.");
Console.ReadLine();
TemperatureSubcriber ts = new TemperatureSubcriber();
ts.Start();
Console.ReadLine();
}
}
In WCF, with a "push" from the server you're really talking about duplex comms; the MarshalByRefObject is largely redundant here (AFAIK). The page here discusses various scenarios, including duplex/callbacks.
If the issue is xml (for some philosophical reason), then simply using NetDataContractSerializer rather than DataContractSerializer might help.
The other approach is to have the clients "pull" data periodically; this works well if you need to support basic http, etc.
What it sounds like you want to do is use WCF NetTcpBinding with Callbacks.
Take a look at this: http://www.codeproject.com/KB/WCF/publisher_subscriber.aspx
"Learning WCF" by Michele Bustamante is also very good. You can get Chpt1 for VS2008 at her website along with the code for the book. Chpt1 will explain/demo setting up connections and such. She also has downloadable sample code. One of the Samples is a DuplexPublishSubscribe.
You will need to modify your logic a bit. If you want to migrate this app to WCF. You will need to have clients pull data from the service at regular intervals.
You will also need a Windows service or application to host the WCF like the console you are using in the previous code.
Well I build real time systems so polling is not an option - I need to push data.
Also I am finding there is no WCF equivalent of System.Runtime.Remoting.ObjRef! This is an extremely useful type that encapsulates a service endpoint and can be serialise and passed around the network to other remoting service.
Think I’ll be sticking with good old remoting until the ObjRef equivalent is introduced.
Yes it is true, just one correction..
ObjRefs are created automatically when any MarshalByRefObject derived object is going outside the appdomain.
So in this case your ITemperatureProvider interface Subscribe method shoud take ITemperatureSubscriber instead of objref.
And then on client side just call p1.Subscribe(this) and the remoting layer will generate ObjRef from the object that will be serialized and sent. (sending b reference)