Static class variable behavior in ASP.NET 2.0?

Question

If I've got this class defined as part of an app in ASP.NET 2.0:

public class Foo
{
   private static int _seed = 100;
   private static object myLock = new object();
   public Foo()
   {
      lock (myLock)
      {
         this.MyInt = _seed;
         _seed++;
      }
   }

   public int MyInt {get; set;}
}

(Edit: updated to account for thread safety concerns as pointed out by answers)

How will that static member behave? Will it start at 100 and increment separately for every session, or will it increment separately for every page refresh, or is it global...?

Note: I'm asking this because I'm using classes to model data for the first time in my ASP.NET app, and I've already discovered that C#'s by-reference nature appears to be ignored by ViewState serialization, so I want to know what other weirdness I can expect. For example, if I have this class defined (assume Bar is another class):

public class OtherFoo
{
   public List<Bar> Bars {get; set;}
}

and I do this on my page:

OtherFoo _myFoo = new OtherFoo();
//Code here to instantiate the list member and add some instances of Bar
Bar b = _myFoo.Bars[0];
ViewState["myFoo"] = _myFoo; //Assume both are [Serializable]
ViewState["myBar"] = b;

When I get those out of ViewState on the next postback, b and _myFoo.Bars[0] are no longer the same object.

John Saunders · Accepted Answer · 2011-06-21 20:13:07Z

3

ASP.NET is not magic. It doesn't magically turn the C# programming language (or any other language) into a language that is aware of web development (sessions, requests, etc).

Your code will behave exactly as it would in any other kind of application, with the addition that it can be called by multiple threads at the same time (so that using "++" is not safe).

Again, there is no magic. Just like every other application, the lifetime of a static is restricted to the lifetime of the AppDomain in which the type containing the static is loaded.

An AppDomain in an ASP.NET application is created the first time the application is accessed (unless the IIS settings force it to pre-start), and only ends at certain times, like when an assembly in the bin folder is changed, or the web.config is changed, or when the IIS settings say that the AppPool needs to be recycled.

edited Jun 21, 2011 at 20:13

answered Jun 21, 2011 at 19:54

John Saunders

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1 Comment

Tom Hamming Over a year ago

I didn't mean to suggest that it was. I know that if this was in a local app, the static variable would increment continuously through the life of that launch of the app. What I'm not sure about is whether that "life of that launch of the app" corresponds to a session (which is what I'm hoping for...this example does not illustrate how I'm using this concept). But thanks for pointing out the thread safety concern too.

Elian Ebbing · Accepted Answer · 2011-06-21 20:08:14Z

1

It will increase the seed every time the constructor is invoked. Note that this can happen in multiple threads, so you better make it thread safe.

Deserialization will cause the (default) constructor to be invoked. If you serialize it to the ViewState, then ASP.NET will deserialize the object on postback, and thus invoke the constructor.

Please note that the C# language and the asp.net framework are on a whole other level. The framework is written (largely) in C#, and it will do a lot for you behind the scenes, but it still follows the rules of the language and the runtime.

Serialization is nothing more than encoding the information of an object (or graph of objects) to a stream. If you deserialize it, you will have the same information back, but it is not the same object you started with. Again, it is no magic, you could write your own serialization library using attributes and reflection.

answered Jun 21, 2011 at 20:08

Elian Ebbing

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2 Comments

Tom Hamming Over a year ago

The key question is: will it start the seed at 100 and then increase it continuously throughout eternity, or will it reset to 100 for every session, or something like that?

Elian Ebbing Over a year ago

No, static fields will exist during the lifetime of the application. Note that you can configure IIS to restart your application after a number of requests is reached, or after a certain interval. This will of course reset the static fields.

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