ASP.NET Serious memory leak

vovachaka · **Posted:** Wed Sep 14, 2005 2:25 am

We built some very simple ASP.NET 1.1 application using NHibernate 0.9.0, npgsql 0.7.0 and postgresql 8.0.3.

Running test on a page where is just one session.CreateCreteria.List() statement for a 5min leads to asp.net process using ~500MB of memory comparing to ~40MB at the test start.

We used some profiler, so I`ll try to describe the situation in more details as possible, hoping some one could tell as whether it is a bug in NHibernate or our misuse.

Hnibernate configuration section in web.config looks like this:

Code:

<nhibernate>
    <add 
      key="hibernate.connection.provider"          
      value="NHibernate.Connection.DriverConnectionProvider" 
    />
    <add 
      key="hibernate.dialect"                      
      value="NHibernate.Dialect.PostgreSQLDialect" 
    />
    <add 
      key="hibernate.connection.driver_class"          
      value="NHibernate.Driver.NpgsqlDriver" 
    />
    <add 
      key="hibernate.connection.connection_string" 
      value="Server=localhost;Port=5432;User id=postgres;Password=postgres;Database=NUSA-dev;ENCODING=UNICODE" 
    />
  </nhibernate>

Nothing unusual...

A common mapping file looks like this:

Code:

<?xml version="1.0" encoding="utf-8" ?> 
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
   <class name="nusa.Data.Classes.Service, nusa" where="is_active='true'" table="service">      
       <id name="ID" column="id" type="Int32" unsaved-value="0"> 
         <generator class="sequence" >
            <param name="sequence">service_id_seq</param>
         </generator> 
      </id>
      <property name="GUID" column="guid"  /> 
      <many-to-one name="Table1" column="table1_id" />
      <many-to-one name="Table2" column="table2_id" />
      <many-to-one name="Person" column="person_id" />
      <property name="Number" column="number" type="Int32" /> 
      <property name="Timestamp1" column="timestemp_1" />
      <many-to-one name="Statuss" column="statuss_id" />
      <property name="Created" column="created" access="nosetter.camelcase" update="false" insert="false" />
      <property name="Modified" access="nosetter.camelcase" insert="false" column="modified" />
   </class>
</hibernate-mapping>

We use session per request model:

Code:

public class NHibernateHttpModule : IHttpModule 
      { 
         private static readonly ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
         // this is only used if not running in HttpModule mode
         private static ISession m_session;

         private static readonly string KEY = "NHibernateSession"; 
 
         public void Init(HttpApplication context) 
         { 
            context.EndRequest += new EventHandler(context_EndRequest); 
         } 
 
         public void Dispose() 
         { 
         } 
 
         private void context_BeginRequest(object sender, EventArgs e) 
         { 
            HttpApplication application = (HttpApplication)sender; 
            HttpContext context = application.Context; 
 
            context.Items[KEY] = BaseDataAccess.OpenSession(); 
         } 
 
         private void context_EndRequest(object sender, EventArgs e) 
         { 
            HttpApplication application = (HttpApplication)sender; 
            HttpContext context = application.Context; 
 
            ISession session = context.Items[KEY] as ISession; 
            if (session != null) 
            { 
               try 
               { 
                  session.Close(); 
               } 
               catch {
                  log.Error("Neizdevas nobeigt NHibernate sesiju");
               } 
            } 
 
            context.Items[KEY] = null; 
         } 
 
         public static ISession CurrentSession 
         { 
            get 
            { 

               if (HttpContext.Current==null)
               {
                  // running without an HttpContext (non-web mode)
                  // the nhibernate session is a singleton in the app domain
                  if (m_session!=null)
                  {
                     return m_session;
                  }
                  else
                  {
                     m_session = BaseDataAccess.OpenSession(); 

                     return m_session;
                  }
               }
               else
               {
                  // running inside of an HttpContext (web mode)
                  // the nhibernate session is a singleton to the http request
                  HttpContext currentContext = HttpContext.Current; 
            
                  ISession session = currentContext.Items[KEY] as ISession; 
 
                  if (session == null) 
                  { 
                     session = BaseDataAccess.OpenSession(); 
                     currentContext.Items[KEY] = session; 
                  } 
 
                  return session; 
               }
            } 
         } 
 
      }

BaseDataAccess.OpenSession:

Code:

public static ISession OpenSession()
      {
         Configuration config;
         ISessionFactory factory;
         ISession session;
   
         config = new Configuration();

         if (config==null)
         {
            throw new InvalidOperationException("NHibernate configuration is null.");
         }

         config.AddAssembly("nusa");
         
         factory = config.BuildSessionFactory();
         
         if (factory==null)
         {
            throw new InvalidOperationException("Call to Configuration.BuildSessionFactory() returned null.");
         }

         session = factory.OpenSession();

         factory.Close();

         if (session==null)
         {
            throw new InvalidOperationException("Call to factory.OpenSession() returned null.");
         }

         return session;
      }

Page that was tested contains:

Code:

IList operatoriList = NHibernateHttpModule.CurrentSession.CreateCriteria(typeof(SomeType))   
                  .AddOrder(Order.Asc("SomeProperty")).List();

As i told after 5 minutes of testing with Application Test Center using 10 simulated users we experianced huge memory leak.

You might find interesting what did profiler shows us:

Class(only anomalies =>1000 instances) Number of instances

Look like we or NHibernate do not close/dispose queries/instances or some thing else...

Any comments or suggestions?

vovachaka · **Posted:** Wed Sep 14, 2005 7:33 am

After hours of browsing internet, coding and testing...

We still don`t know what was wrong, but the following changes resolved memory leak. After about ten test each of them taking ~500MB of memory before, now do just a ~150MB memory peak running in a row.

BaseDataAccess do not contains OpenSession any more, and NHibernateHttpModule now look like this:

Code:

using NHibernate.Cfg;
   using System;
   using System.Web;   
   using NHibernate;
   using log4net;
       
      /// <summary>
      /// Summary description for NHibernateHttpModule.
      /// </summary>
      public class NHibernateHttpModule : IHttpModule 
      { 
         private static readonly ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
         // this is only used if not running in HttpModule mode
         private static ISession m_session;

         private static ISessionFactory factory;
         private static Configuration config;

         private static readonly string KEY = "NHibernateSession"; 
 
         public void Init(HttpApplication context) 
         { 
            context.EndRequest += new EventHandler(context_EndRequest); 
         } 

         private static ISession OpenSession()
         {
            
            ISession session;
   
            if (config == null)
               config = new Configuration();

            if (config==null)
            {
               throw new InvalidOperationException("NHibernate configuration is null.");
            }

            config.AddAssembly("nusa");
         
            if (factory == null)
               factory = config.BuildSessionFactory();
         
            if (factory==null)
            {
               throw new InvalidOperationException("Call to Configuration.BuildSessionFactory() returned null.");
            }

            lock (typeof(NHibernateHttpModule))
            {
               session = factory.OpenSession();
            }

            if (session==null)
            {
               throw new InvalidOperationException("Call to factory.OpenSession() returned null.");
            }

            return session;
         }
 
         public void Dispose() 
         { 
            if (factory != null)
               factory.Close();
         } 
 
         private void context_BeginRequest(object sender, EventArgs e) 
         { 
            HttpApplication application = (HttpApplication)sender; 
            HttpContext context = application.Context; 
 
            context.Items[KEY] = OpenSession(); 
         } 
 
         private void context_EndRequest(object sender, EventArgs e) 
         { 
            HttpApplication application = (HttpApplication)sender; 
            HttpContext context = application.Context; 
 
            ISession session = context.Items[KEY] as ISession; 
            if (session != null) 
            { 
               try 
               { 
                  session.Close(); 
               } 
               catch {
                  log.Error("Neizdevas nobeigt NHibernate sesiju");
               } 
            } 
 
            context.Items.Remove(KEY); 
         } 
 
         public static ISession CurrentSession 
         { 
            get 
            { 

               if (HttpContext.Current==null)
               {
                  // running without an HttpContext (non-web mode)
                  // the nhibernate session is a singleton in the app domain
                  if (m_session!=null)
                  {
                     return m_session;
                  }
                  else
                  {
                     m_session = OpenSession(); 

                     return m_session;
                  }
               }
               else
               {
                  // running inside of an HttpContext (web mode)
                  // the nhibernate session is a singleton to the http request
                  HttpContext currentContext = HttpContext.Current; 
            
                  ISession session = currentContext.Items[KEY] as ISession; 
 
                  if (session == null) 
                  { 
                     session = OpenSession(); 
                     currentContext.Items[KEY] = session; 
                  } 
 
                  return session; 
               }
            } 
         } 
 
      }     

Try to find differences your self :)

sergey · **Posted:** Wed Sep 14, 2005 8:24 am

How did your BaseDataAccess.OpenSession look before? It almost looks as if you were creating a new ISessionFactory for each request.

By the way, you don't need a lock around factory.OpenSession, it's a thread-safe operation. And you need a lock around the code building the session factory, otherwise you might accidentally create several instances of the factory.

Dan · **Joined:** Thu Aug 25, 2005 5:05 am **Posts:** 6

In the first version you created a factory per request.

In the second version you reparse your domain assembly per request.

Try changing your OpenSession in the second version to:

Code:

         private static ISession OpenSession()
         {
            
            lock (typeof(NHibernateHttpModule))
            {
               if (factory == null)
               {
                  Configuration config = new Configuration();
               
                   config.AddAssembly("nusa");
               
                   factory = config.BuildSessionFactory();
               }
            }
   
            return factory.OpenSession();

         }

Edit: Oops, sergey was right (below), I put the lock in the wrong place.

sergey · **Posted:** Wed Sep 14, 2005 11:38 am

You need to extend that lock to cover the "if (factory == null)", otherwise it doesn't really help anything.

jnapier · **Joined:** Sat Sep 10, 2005 3:46 pm **Posts:** 178

It seems like a bad design to have your http module opening factories and sessions for you. You should at least move the OpenSession operation back out to the data access class.

I never liked the idea of having the BeginRequest opening sessions. What if you naviagate to a page that doesn't need a session?
I see this httpmodule design passed all around the internet and wonder why people do it.

I believe the Provider pattern works so good for handling sessions. this is the architecture.

abstract SessionProvider
HttpSessionProvider
StaticSessionProvider

SessionManager

You provide configuration for the provider that you want to use in your config file. then you can swap out strategies by editing the config file. This works great when you have an app with different UI's. I consider NUnit another UI so it works great for running test code also.

You just ask the Session manager for sessions and its smart enough to know how to use the correct provider. I've even extended this so that the SessionProvider is hooked to a ConnnectionProvider. This way the correct connection string can be determined at runtime based on the environment the app is running in: local, integration, staging productions, etc...

tinomen · **Joined:** Tue May 24, 2005 12:55 pm **Posts:** 56

Quote:

I see this httpmodule design passed all around the internet and wonder why people do it.

I think most are using it because someone provided the code to use it and the session-per-request is a good solution. Post the code to use your implementation of the Provider pattern and you might find people using the Provider pattern more often. I personally would be interested as I don't use the HttpModule method either.

jnapier · **Joined:** Sat Sep 10, 2005 3:46 pm **Posts:** 178

I will post some code shortly. There are a bunch of differenet classes in this implementation and theres to much to post here so I'll try to trim it down to the main code elements.

Just to clarify, I do use an httpmodule when implmenting my HttpSessionProviderClass, but its only to close out a session that hasn't been closed.

I'll get the code out as soon as I can.

shadow · **Joined:** Wed Sep 07, 2005 9:23 pm **Posts:** 3

Dear Dan,

Your suggested modification would be:

Code:

         private static ISession OpenSession()
         {
           if (factory == null)
               lock (typeof(NHibernateHttpModule))
               {
                  Configuration config = new Configuration();
               
                   config.AddAssembly("nusa");
               
                   factory = config.BuildSessionFactory();
               }
            }
   
            return factory.OpenSession();

         }

I

sergey · **Posted:** Mon Sep 19, 2005 3:44 am

It should be:

Code:

lock(typeof(NHibernateHttpModule))
{
    if (factory == null)
    {
    ...
    }
}

xor · **Posted:** Wed Sep 21, 2005 8:43 am

Sergey, one little correction: MS warns agains locking on the type object. It could create cross-AppDomain deadlocks. Use static locker object instead. Original article could be found on the MSDN site (i think it was published in the Dr.GUI's column).

tinomen · **Joined:** Tue May 24, 2005 12:55 pm **Posts:** 56

When I get some time I want to start a wiki page about session management. there are various forumn posts that should be compiled together. For now there is the Using NHibernate with ASP.Net which lightly covers session handling. There is a link there about singletons that everone should read. I recently switched to using a nested singleton because a co-worker confirmed that the double-check locking mechanism does not work in .NET. This page also gives some explanation why xor is right.

michael1d · **Joined:** Mon Jun 20, 2005 8:47 pm **Posts:** 11

I was reading this about using lock:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/cpconthreadingdesignguidelines.asp

So maybe

Code:

System.Threading.Interlocked.CompareExchange(ref x, y, null);

would be a better alternative.

Kalle · **Posted:** Fri Sep 30, 2005 5:11 am

Im a little bit confused after browsing the site. On the pages that cover SysCache http://wiki.nhibernate.org/display/NHC/SysCache+Usage it states that "The default ISessionFactory implementation is not threadsafe so be sure to acquire a lock on this while creating new ISession instances". To me it sound like you also have to sycnchronize the session creation part :

Code:

lock(myLock){
    return factory.OpenSession(); 
}

That is not right is it?

/Kalle

sergey · **Posted:** Fri Sep 30, 2005 5:39 am

I too think it's wrong, see my comment there.