ASP.NET静态对象行为

Question

I have the following class as part of an asp.net application.

public sealed class SomeClass    
 {
    private static string appId = Guid.NewGuid().ToString();

    public static ReadSomethingFromDb(){}

    public static WriteSomethingToDb(){}
}

There are more than one application instances in the same application pool, and they all access the same database. I want the operations performed by the above class to be uniquely tied to the instance that performed it, hence the use of the appId. So adding a record to the database would for example contain a name, address and appId. This has been simplified for discussion purposes.

Assuming that I have two instances running at mysite.a and mysite.b the above class would generate two different guids.

My problem is that mysite.a sometimes produces more than one guid, which is unexpected.

Thank you in advance

Answer 1

That will get a new Guid per AppDomain ; you'll have new AppDomain s whenever:

• the app-pool recycles
• different machines
• you reboot the server
• you edit a file such as web.config
• IIS just feels like spawning another one

In short, this isn't a very robust way of proving that one app is the same (although it indicate different applications clearly).

Why not just something like the site path or IIS name as an identifier?

Answer 2

A new AppDomain is created under various circumstances. For instance, when the web.config is changed. At that time, no new requests are scheduled for the original AppDomain; and all new requests are sent to the new one.

During the transition, both AppDomains will still be running.

Answer 3

after Marc's comment i ended up using this at application start which seems to work

string applicationId = Environment.MachineName+""
    +System.Web.HttpContext.Current.Request.ApplicationPath;

this covered me as there is a chance of a multi machine setup plus the application instances which depends on the path.