WCF服务的多个应用程序域导致并发问题

Question

I have a WCF Service Endpoint that is defined with the following ServiceBehavior attribute.

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Multiple)]

I am having issues with a call within my service that needs to guarantee that an object is only created once. The following code is called within my service.

public class MySingletonDataProvider{
     private static MySingletonDataProvider _instance;
     private static readonly object _lock = new object();

     public static MySingletonProvider Create(){

          lock(_lock){

              if(_instance == null){
                 _instance = new MySingletonProvider();
                 Log.Info("New Instance Created " + AppDomain.CurrentDomain.FriendlyName");
              }

              return _instance;
          }
     }
}

When this is hit, we are typically getting 3-5 logs such as the following:

- "New Instance Created 123252352323623"
- "New Instance Created 423523562362362"
- "New Instance Created 235623623462366"

Showing that multiple AppDomains are able to execute the code within the lock. This is causing huge issues. What is the solution so that I can guarantee that this instance is only created once?

Answer 1

CLR creates new MySingletonDataProvider instance for each AppDomain, thus you have separate locking objects. I'd suggest to use some kind of inter-process synchronization primitives, as mutexes, for example. http://msdn.microsoft.com/en-us/library/system.threading.mutex.aspx