Nhibernate，SQL Server和IIS 7.5连接泄漏：从应用程序池获取连接之前超时

Question

I have an MVC application deployed on 3 separate servers (Test, Staging and Production Environment). Test and Staging server are doing fine but occassionally, the production server do pull this error

System.InvalidOperationException Timeout expired. The timeout period elapsed prior to obtaining a connection >from the pool. This may have occurred because all pooled connections were in >use and max pool size was reached.

The full stack trace as captured by elmah is as shown below.

The production server is on SQL Server 2008 and IIS 7.5.

My Nhibernate Driver connector is as shown below

 <?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property    name="dialect">NHibernate.Dialect.MsSql2008Dialect,NHibernate</property>
    <property name="adonet.batch_size">0</property>
    <property name="show_sql">true</property> 
    <mapping assembly="BusinessLogic"/>
</session-factory>
</hibernate-configuration>

Here is my Get current session Method

 public static ISession GetCurrentSession()
        {
            HttpContext context = HttpContext.Current;
            ISession currentSession = context.Items[CURRENT_NHIBERNATE_SESSION_KEY] as ISession;

            if (currentSession == null)
            {
                currentSession = sessionFactory.OpenSession();
                context.Items[CURRENT_NHIBERNATE_SESSION_KEY] = currentSession;
            }
            if (currentSession.Connection.State == System.Data.ConnectionState.Closed)
            {
                currentSession = sessionFactory.OpenSession();
            }
            if (!currentSession.IsConnected)
            {
                currentSession = sessionFactory.OpenSession();
            }
            if (!currentSession.IsOpen)
            {
                currentSession = sessionFactory.OpenSession();
            }
            if (currentSession.IsDirty())
            {
                currentSession.Clear();
            }

            return currentSession;
        }

I used IRepository pattern for all my business logic. One of my method is shown here:

 public IList<CourseRequirement> getCourseRequirement(int requirementId)
            {
                ISession  session = _courseRequirment.CurrentSession;
                var cr = session.QueryOver<CourseRequirement>().Where(x => x.RequirementId == requirementId);
                return cr.List<CourseRequirement>();
            }

In addition, I am using autofac for dependency injection. I can also see this in the inner exception every time it happens.

System.InvalidOperationException: An error occurred when trying to create a controller of type 'ASSEMBLY.Controllers.AccountController'. Make sure that the controller has a parameterless public constructor. ---> Autofac.Core.DependencyResolutionException: An exception was thrown while invoking the constructor 'Void .ctor()' on type 'NHibernateRepository`2'. ---> Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached. (See inner exception for details.) ---> System.InvalidOperationException: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.

What I have done

I have checked these link , link and many more. Others like how-to-fix-sql-connection-leaks-in-this-code suggested putting the sql in using statements. Almost, all the links suggested connection leak in the application and recommends putting all transaction in a using statement.

Implement that implies rewriting most methods in my business logic.

I am worried because this is not the only application I have written this way and besides Test and staging environment are fine. From logging report, this often happens when the site is on low traffic eg 6:00 am, 3.00 am but the time is not fixed.

Kindly help

Update This is my autofac Dependency resolver(I can see from the inner exception that autofac could not instantiate some services occasionally

 public class FormDependencyResolver
    {
        public static void RegisterDependencies()
        {

            var builder = new ContainerBuilder();

            builder.RegisterControllers(typeof(MvcApplication).Assembly);


            builder.Register(c =>
                //register FakeHttpContext when HttpContext is not available
                HttpContext.Current != null ?
                (new HttpContextWrapper(HttpContext.Current) as HttpContextBase) :
                (new FakeHttpContext("~/") as HttpContextBase))
                .As<HttpContextBase>()
                .InstancePerLifetimeScope();
            builder.Register(c => c.Resolve<HttpContextBase>().Request)
                .As<HttpRequestBase>().InstancePerLifetimeScope();

            builder.Register(c => c.Resolve<HttpContextBase>().Response)
                .As<HttpResponseBase>()
                .InstancePerLifetimeScope();
            builder.Register(c => c.Resolve<HttpContextBase>().Server)
                .As<HttpServerUtilityBase>()
                .InstancePerLifetimeScope();
            builder.Register(c => c.Resolve<HttpContextBase>().Session)
                .As<HttpSessionStateBase>()
                .InstancePerLifetimeScope();



            builder.RegisterGeneric(typeof(NHibernateRepository<,>)).As(typeof(IRepository<,>)).InstancePerLifetimeScope();
            builder.RegisterType<AsyncService>().As<IAsyncService>().InstancePerLifetimeScope();//.InstancePerLifetimeScope();
            builder.RegisterType<SMSSender>().As<ISMSSender>().InstancePerLifetimeScope();
            builder.RegisterType<SMSAccount>().As<ISMSAccount>().InstancePerLifetimeScope();
            builder.RegisterType<BusinessLogic.Services.AuthenticationService>().As<IAuthenticationService>().InstancePerLifetimeScope();
            builder.RegisterType<PageHelper>().As<IPageHelper>().InstancePerLifetimeScope();

            builder.RegisterType<UtilityService>().As<IUtilityService>().InstancePerLifetimeScope();
            builder.RegisterType<WebWorker>().As<IWebWorker>().InstancePerLifetimeScope();
            builder.RegisterType<DateTimeHelper>().As<IDateTimeHelper>().InstancePerLifetimeScope();
            builder.RegisterType<UserService>().As<IUserService>().InstancePerLifetimeScope();
            builder.RegisterType<AuditService>().As<IAuditService>().InstancePerLifetimeScope();
            builder.RegisterType<HtmlHelper>().InstancePerDependency();
            builder.RegisterType<PaymentService>().As<IPaymentService>().InstancePerLifetimeScope();

            IContainer container = builder.Build();
            DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

        }
    }

Answer 1

You are opening new session instances in each of those if statements. Several of them can be executed at once because there are not else statements. The previously opened session would go out of scope without calling Dispose() .

The code below is everything you should need. Just make sure to dispose the session instance at the end of the HTTP request.

private static readonly object syncObject = new Object();

public static ISession GetCurrentSession()
{   
     lock (syncObject)
     {
         HttpContext context = HttpContext.Current;
         ISession currentSession = context.Items[CURRENT_NHIBERNATE_SESSION_KEY] as ISession;

         if (currentSession == null)
         {
             currentSession = sessionFactory.OpenSession();
         }

         context.Items[CURRENT_NHIBERNATE_SESSION_KEY] = currentSession;    

         return currentSession;
     }
}