The System.Web.SessionState.SessionStateModule object calls the SessionStateStoreProviderBase.SetItemExpireCallback(SessionStateItemExpireCallback) method when the module is initialized to determine whether calls to the Session_OnEnd event are supported by the System.Web.SessionState.SessionStateStoreProviderBase implementation and to associate the System.Web.SessionState.SessionStateItemExpireCallback delegate with the Session_OnEnd event.

Custom session-state store provider implementers should use the SessionStateStoreProviderBase.SetItemExpireCallback(SessionStateItemExpireCallback) method to inform the System.Web.SessionState.SessionStateModule object whether calls to the Session_OnEnd event are supported and to set a local reference to the System.Web.SessionState.SessionStateItemExpireCallback delegate supplied by the expireCallback parameter. The custom implementation must decide when the local System.Web.SessionState.SessionStateItemExpireCallback delegate will be called. For example, the delegate could be called during the call to the SessionStateStoreProviderBase.RemoveItem(System.Web.HttpContext, string, object, SessionStateStoreData) method, which is called when a session is abandoned.