WCF Singleton question

[Grofit]

Hey,

I have a number of services within the same project, and i have some data that i would like to be shared in one place, so all the services in the project can access it. Im not really sure if it is possible but can i just simply do something like define a static object in the singleton service then from another service just do something like:



ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
class MySingleton : IMyContract
{
static MyClass m_Object;

public MySingleton( )
{
m_Object = new MyClass();
}
}

class MyPerCall : IMyOtherContract
{
public int GetSomeData()
{
return MySingleton.m_Object.SomeIntProperty;
}
}


I dont mind using named pipes or whatever if needed, i just want the fastest way of being able to have a few persistant objects that are partially accessible to other services.

[Grofit]

Quick bump, just so i can get any useful intel before i try implementing something like this later one...

[dannystommen]

When you search msdn on singleton you will find the next example
http://msdn.microsoft.com/en-us/library/ms998558.aspx

Implementing this in you case would mean


public class MySingleton : IMyContract
{
private static MySingleton instance;
private static readonly object _lock = new object();
public static MySingleton Instance
{
get
{
lock(_lock){
if (instance == null)
{
instance = new MySingleton ();
}
return instance;
}
}
}
}

[boudino]

1. I would prefer to use WCF's itself to manage lifecycle services, including singleton.
2. I would delegate the share data other than service implementatin class, which can be singleton.
3. I would think about using RDBM for storing shared data.

[Grofit]

Ah all good stuff guys thanks alot... i basically have some server logic already, but it has hooks where data needs to be fed in and gets fed out, so i want to basically wrap it in a WCF singelton that stores the main object as a wrapper, then have lots of smaller WCF services to make use of each chunk of relevent data in the object...

So an example would be something like pulling a name and an ID from the object to use in a service that displays other stuff from the DB pertaining to the ID... if that makes sense...

One other thing that im just curious about:

When you search msdn on singleton you will find the next example
http://msdn.microsoft.com/en-us/library/ms998558.aspx

Implementing this in you case would mean


public class MySingleton : IMyContract
{
private static MySingleton instance;
private static readonly object _lock = new object();
public static MySingleton Instance
{
get
{
lock(_lock){
if (instance == null)
{
instance = new MySingleton ();
}
return instance;
}
}
}
}




In this example wouldnt the WCF service create its own instance when its called, so when you try to get the instance you would have 2 singletons going? or can you just do something like:


public class MySingleton : IMyContract
{
private static readonly object _lock = new object();
public static MySingleton Instance
{
get { return this; }
}
}

[dannystommen]

In this example wouldnt the WCF service create its own instance when its called, so when you try to get the instance you would have 2 singletons going? or can you just do something like:


public class MySingleton : IMyContract
{
private static readonly object _lock = new object();
public static MySingleton Instance
{
get { return this; }
}
}


[/QUOTE]

Have you tried to compile it? You will get an error : "Keyword 'this' is not valid in a static property, static method, or static field initializer"

[Grofit]

Have you tried to compile it? You will get an error : "Keyword 'this' is not valid in a static property, static method, or static field initializer"

hahah i cant believe i didnt realise that when typing, could you do something like OperationContext.CurrentHost or something like that? (i cant remember exact syntax). I dont have anything against changing the constructor to assign to the _instance if needed...

Although saying that im just assuming that it has made 2 singleton instances in your previous example, one for the WCF service and one for the _instance, so if im wrong then there is no problem...

Also im not at my dev computer atm im at work, i just like to think ahead so whatever knowledge i get from you guys i will be using when i try to implement later.

[Arjay]

I'd separate the WCF class implementation with the underlying functionality implementation.

Just create the WCF Service as you've mentioned...

[ServiceBehavior( InstanceContextMode = InstanceContextMode.Single )]

and then have its methods call into the static singleton class as Danny described. What that class does internally is up to you (internally it can call another WCF class).