RavenDB - EmbeddableDocumentStore already disposed or NRE

Question

This question is about creating a single instance of the Raven document store in the lifetime of a ASP.Net MVC application and subsequently using a new IDocumentSession per request to serve the client with. I believe to have followed the recommended procedure described at http://ravendb.net/kb/3/using-ravendb-in-an-asp-net-mvc-website I'm still experiencing errors once the site is deployed.

My code looks as follows. The HepApp class contains the document store and is referenced by the application:

internal class HepApp
{
    internal static readonly Object padlock = new object();
    private static IDocumentStore _DB;

    internal IDocumentStore DB
    {
        get
        {
            if (_DB == null)
            {
                lock (padlock)
                {
                    if (_DB == null)
                    {
                        _DB = new EmbeddableDocumentStore().Initialize();
                        return _DB;
                    }
                }                    
            }
            return _DB;
        }
    }

    public IDocumentSession GetSession()
    {
        return DB.OpenSession();
    }
}

My MVC Controller:

public class HomeController : Controller
{
    IDocumentSession RavenSession;

    public HomeController()
    {
    }

    protected void Init()
    {
        RavenSession = MvcApplication.HepApp.GetSession();
    }

    protected override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        base.OnActionExecuting(filterContext);
        Init();
    }

The application class Global.asax binds to:

public class MvcApplication : System.Web.HttpApplication
{
    static readonly Object padlock = new object();
    static HepApp _HepApp;

    internal static HepApp HepApp
    {
        get
        {
            if(_HepApp == null)
            {
                lock(padlock)
                {
                    if(_HepApp == null)
                    {
                        _HepApp = new HepApp();
                    }
                }
            }

            return _HepApp;
        }
    }

When the application starts the document store should be initialized and live for the remainder of the application's lifetime. For each request a new Session object is created. At least, that's the idea. Instead null reference errors occur in OnActionExecuting (though I suspect the HomeController.Init method but it doesn't appear on the stack) or the EmbeddableDocumentStore object is reported als already disposed. Confusingly, these errors only crop up after the application has been running for a while which might suggest it's an app pool recycle issue

EDIT: The errors differ but all seem to indicate a problem with the instantiation of the database store :

[EsentFileAccessDeniedException: Cannot access file, the file is locked or in use] [InvalidOperationException: Could not write to location: \192.168.0.100\localuser\x\App_Data/Raven. Make sure you have read/write permissions for this path.]

System.InvalidOperationException: Could not write to location: \192.168.0.100\localuser\x\App_Data/Raven. Make sure you have read/write permissions for this path. ---> Microsoft.Isam.Esent.Interop.EsentFileAccessDeniedException: Cannot access file, the file is locked or in use at Microsoft.Isam.Esent.Interop.Api.Check(Int32 err) at Microsoft.Isam.Esent.Interop.Api.JetInit(JET_INSTANCE& instance) at Raven.Storage.Esent.TransactionalStorage.Initialize(IUuidGenerator uuidGenerator, OrderedPartCollection1 documentCodecs) --- End of inner exception stack trace --- at Raven.Storage.Esent.TransactionalStorage.Initialize(IUuidGenerator uuidGenerator, OrderedPartCollection1 documentCodecs) at Raven.Database.DocumentDatabase..ctor(InMemoryRavenConfiguration configuration, TransportState transportState) at Raven.Client.Embedded.EmbeddableDocumentStore.InitializeInternal() at Raven.Client.Document.DocumentStore.Initialize() at HEPlaceHolder.HepApp.get_DB() in e:\projects\HEPlaceHolder\HEPlaceHolder\Logic\HepApp.cs:line 27 at HEPlaceHolder.Controllers.HomeController.OnActionExecuting(ActionExecutingContext filterContext) in e:\projects\HEPlaceHolder\HEPlaceHolder\Controllers\HomeController.cs:line 31 at System.Web.Mvc.Controller.System.Web.Mvc.IActionFilter.OnActionExecuting(ActionExecutingContext filterContext) at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.InvokeActionMethodFilterAsynchronouslyRecursive(Int32 filterIndex) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass33.b__31(AsyncCallback asyncCallback, Object asyncState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters, AsyncCallback callback, Object state) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.b__19(AsyncCallback asyncCallback, Object asyncState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction(ControllerContext controllerContext, String actionName, AsyncCallback callback, Object state) at System.Web.Mvc.Controller.b__1c(AsyncCallback asyncCallback, Object asyncState, ExecuteCoreState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Controller.BeginExecuteCore(AsyncCallback callback, Object state) at System.Web.Mvc.Controller.b__14(AsyncCallback asyncCallback, Object callbackState, Controller controller) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Controller.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) at System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.b__4(AsyncCallback asyncCallback, Object asyncState, ProcessRequestState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

[ObjectDisposedException: The document store has already been disposed and cannot be used Object name: 'EmbeddableDocumentStore'.] Raven.Client.DocumentStoreBase.EnsureNotClosed() +82 System.Web.Mvc.Async.WrappedAsyncResultBase`1.Begin(AsyncCallback callback, Object state, Int32 timeout) +128

[NullReferenceException: Object reference not set to an instance of an object.] HEPlaceHolder.Controllers.HomeController.OnActionExecuting(ActionExecutingContext filterContext) in e:\projects\HEPlaceHolder\HEPlaceHolder\Controllers\HomeController.cs:31 System.Web.Mvc.Controller.System.Web.Mvc.IActionFilter.OnActionExecuting(ActionExecutingContext filterContext) +10

System.InvalidOperationException: Could not open transactional storage: \192.168.0.100\localuser\x\App_Data/Raven\Data ---> Microsoft.Isam.Esent.Interop.EsentTempPathInUseException: Temp path already used by another database instance at Microsoft.Isam.Esent.Interop.Api.Check(Int32 err) at Microsoft.Isam.Esent.Interop.Api.JetInit(JET_INSTANCE& instance) at Raven.Storage.Esent.TransactionalStorage.Initialize(IUuidGenerator uuidGenerator, OrderedPartCollection1 documentCodecs) --- End of inner exception stack trace --- at Raven.Storage.Esent.TransactionalStorage.Initialize(IUuidGenerator uuidGenerator, OrderedPartCollection1 documentCodecs) at Raven.Database.DocumentDatabase..ctor(InMemoryRavenConfiguration configuration, TransportState transportState) at Raven.Client.Embedded.EmbeddableDocumentStore.InitializeInternal() at Raven.Client.Document.DocumentStore.Initialize() at HEPlaceHolder.HepApp.get_DB() in e:\projects\HEPlaceHolder\HEPlaceHolder\Logic\HepApp.cs:line 27 at HEPlaceHolder.Controllers.HomeController.OnActionExecuting(ActionExecutingContext filterContext) in e:\projects\HEPlaceHolder\HEPlaceHolder\Controllers\HomeController.cs:line 31 at System.Web.Mvc.Controller.System.Web.Mvc.IActionFilter.OnActionExecuting(ActionExecutingContext filterContext) at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.InvokeActionMethodFilterAsynchronouslyRecursive(Int32 filterIndex) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass33.b__31(AsyncCallback asyncCallback, Object asyncState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters, AsyncCallback callback, Object state) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.b__19(AsyncCallback asyncCallback, Object asyncState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction(ControllerContext controllerContext, String actionName, AsyncCallback callback, Object state) at System.Web.Mvc.Controller.b__1c(AsyncCallback asyncCallback, Object asyncState, ExecuteCoreState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Controller.BeginExecuteCore(AsyncCallback callback, Object state) at System.Web.Mvc.Controller.b__14(AsyncCallback asyncCallback, Object callbackState, Controller controller) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.Controller.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) at System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.b__4(AsyncCallback asyncCallback, Object asyncState, ProcessRequestState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallBeginDelegate(AsyncCallback callback, Object callbackState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase1.Begin(AsyncCallback callback, Object state, Int32 timeout) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

EDIT: Whenever the bin folder is updated with a tweaked version to debug the problem the site will initially run ok, presumably because the application is reset.