WebAPI memory leak in BuildManager - asp.net-web-api

Question

I have a precompiled web app (32 bit) where the memory usage slowly rises until I get OutOfMemoryExceptions. Using a profiler, I've observed that the prime suspect is strings in System.Web.VirtualPath objects, which are in turn stored in the _localResourcesAssemblies Hashtable in a System.Web.Compilation.BuildManager object.
Those entries seem to get added in batches of about 50 MB, once every 4-6 hours. I'm stuck -- I have no clue what is calling into the BuildManager which adds those entries. Looking at the entries, they contain paths that match valid routes of an attribute-routed controller (or parent paths of valid route paths).
No files should be changing in the application's directory.
I set up a simple web app with similar routes to see if I could reproduce the problem, but I haven't been able to reproduce the problem on the test app.
Any ideas on how I can find what is calling into the BuildManager (sealed class, probably singleton) object?

Answer 1

Workaround: Remove the Microsoft.AspNet.WebPages nuget package (and pages that depend on it, including the Microsoft.AspNet.WebApi.HelpPage package).
We finally got a stack trace with the Out of Memory coming from the true cause of the problem (most of our traces were in our own code where we allocate several MB at a time). Stack trace posted below.
We were able to find that the WebPages HTTP module gets added dynamically and registers the callback which was adding every url path to a cache in BuildManager, and due to our 32 bit memory space and huge number of unique paths, this would eventually run us out of memory.
As promised, the stacktrace that finally was able to lead us to the cause of the issue:
Exception type: OutOfMemoryException
Exception message: Exception of type 'System.OutOfMemoryException' was thrown.
at System.Collections.Hashtable.rehash(Int32 newsize, Boolean forceNewHashCode)
at System.Collections.Hashtable.expand()
at System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add)
at System.Collections.Hashtable.set_Item(Object key, Object value)
at System.Web.Compilation.BuildManager.EnsureFirstTimeDirectoryInit(VirtualPath virtualDir)
at System.Web.Compilation.BuildManager.GetBuildResultFromCacheInternal(String cacheKey, Boolean keyFromVPP, VirtualPath virtualPath, Int64 hashCode, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVPathBuildResultFromCacheInternal(VirtualPath virtualPath, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound)
at System.Web.Compilation.BuildManager.GetObjectFactory(String virtualPath, Boolean throwIfNotFound)
at System.Web.WebPages.BuildManagerWrapper.GetObjectFactory(String virtualPath)
at System.Web.WebPages.BuildManagerWrapper.ExistsInPrecompiledSite(String virtualPath)
at System.Web.WebPages.BuildManagerWrapper.Exists(String virtualPath)
at System.Web.WebPages.VirtualPathFactoryManager.Exists(String virtualPath)
at System.Web.WebPages.DefaultDisplayMode.GetDisplayInfo(HttpContextBase httpContext, String virtualPath, Func`2 virtualPathExists)
at System.Web.WebPages.DisplayModeProvider.GetDisplayInfoForVirtualPath(String virtualPath, HttpContextBase httpContext, Func`2 virtualPathExists, IDisplayMode currentDisplayMode, Boolean requireConsistentDisplayMode)
at System.Web.WebPages.DisplayModeProvider.GetDisplayInfoForVirtualPath(String virtualPath, HttpContextBase httpContext, Func`2 virtualPathExists, IDisplayMode currentDisplayMode)
at System.Web.WebPages.WebPageRoute.GetRouteLevelMatch(String pathValue, String[] supportedExtensions, Func`2 virtualPathExists, HttpContextBase context, DisplayModeProvider displayModeProvider)
at System.Web.WebPages.WebPageRoute.MatchDefaultFiles(String pathValue, String[] supportedExtensions, Func`2 virtualPathExists, HttpContextBase context, DisplayModeProvider displayModes, String currentLevel)
at System.Web.WebPages.WebPageRoute.MatchRequest(String pathValue, String[] supportedExtensions, Func`2 virtualPathExists, HttpContextBase context, DisplayModeProvider displayModes)
at System.Web.WebPages.WebPageRoute.DoPostResolveRequestCache(HttpContextBase context)
at System.Web.WebPages.WebPageHttpModule.OnApplicationPostResolveRequestCache(Object sender, EventArgs e)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)