I hadn’t done any profiling on EZWeb in a while, so I thought that I had better do some.  I like Application Center Test that comes with VS 2003 EA, and I also watch my performance counters while it’s running.  I tell you, it’s easy to cause a memory leak in .Net.  I predict that fixing .Net memory leaks will be a sizable consulting niche in the near future as more .Net apps go into production.  Especially web applications where the Page object is being created and handed over to the garbage collector many hundred times per second.  I found a really nasty memory leak in EZWeb this morning, and it can happen to anyone with normal code.  If you are currently using version 0.9 or 1.0 of EZWeb, I’ll tell you what code to change to fix it, and I’m going to post a v1.1 release to GotDotNet as well.  So, here is the scenario.  I define my own user object, and to conform to Forms-based authentication, I never wanted my User property to be null – System.Web.UI.Page.User is never null.  If no one is authenticated, it comes back with an empty GenericPrincipal object.  I created an “Empty” property of my User (WebPrincipal) object much like string.Empty and Color.Empty, so whenever there is no user logged in, the User will be WebPrincipal.Empty:

protected static WebPrincipal m_empty = WebPrincipal.InstantiateEmpty();

Then I have my Empty property, so I can test against WebPrincipal.Empty because as a static member, there will only be one instance.  Well, I forgot about some code from when my User property was null:

        private void SetUserEventListeners()


        {


            if(m_user != null)


            {


                m_user.LoggingOut += new EventHandler(User_LoggingOut);


                m_user.LoggedOut += new EventHandler(User_LoggedOut);


            }


        }

So, this is what happens:  m_user is an instance of WebPrincipal.Empty (a referenced by a static member that lives as long as the AppDomain).  I am adding delegates in my Page class to events of WebPrincipal.Empty, so a persistent instance is maintaining references to methods of my Page class (EVERY SINGLE INSTANCE OF MY PAGE CLASS).  What does this mean?  It means that the garbage collector see that references are held to the Page instances, so it doesn’t garbage collect them.  The gen 2 heap keeps getting bigger and bigger and bigger. 

So watch out for this in your code.  If you have long-lived objects that have references to short-lived objects, those short-lived objects become long-lived!

To fix this code, I only wire up event handlers when the User object is an actual good instance of WebPrincipal:

        private void SetUserEventListeners()


        {


            if (m_user.Identity.IsAuthenticated)


            {


                m_user.LoggingOut += new EventHandler(User_LoggingOut);


                m_user.LoggedOut += new EventHandler(User_LoggedOut);


            }


        }

The Empty instance will have it’s IsAuthenticated property as false, so if it is true, then I know I have a good instance.  Now I profile the app, and my gen 2 managed heap stays right where it should be.