System.ExecutionEngineException: Attempting to JIT compile method 'System.Linq.Enumerable:<ToLookup`2> - xamarin.ios

Question

here is my Code
public int GetUsersSqlCount()
{
// Here i get the Error
return this.GetUsersSql().Count();
}
public IEnumerable<CsUser> GetUsersSql()
{
return (from x in this._storage.CsUsers
join y in this._storage.CeMitarbs on x.MitNr equals y.MitNr
select x).OrderBy(x => x.KurzZch);
}
I get the following Error:
Unhandled Exception: System.ExecutionEngineException: Attempting to JIT compile method 'System.Linq.Enumerable:<ToLookup`2>m__5A<Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CeMitarb, System.Nullable`1<int>> (Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CeMitarb)' while running with --aot-only.
at System.Linq.Enumerable.ToLookup[CeMitarb,Nullable`1,CeMitarb] (IEnumerable`1 source, System.Func`2 keySelector, System.Func`2 elementSelector, IEqualityComparer`1 comparer) [0x00079] in /Developer/MonoTouch/Source/mono/mcs/class/System.Core/System.Linq/Enumerable.cs:2966
at System.Linq.Enumerable.ToLookup[CeMitarb,Nullable`1] (IEnumerable`1 source, System.Func`2 keySelector, IEqualityComparer`1 comparer) [0x00000] in /Developer/MonoTouch/Source/mono/mcs/class/System.Core/System.Linq/Enumerable.cs:2934
at System.Linq.Enumerable+<CreateJoinIterator>c__Iterator18`4[Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser,Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CeMitarb,System.Nullable`1[System.Int32],Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser].MoveNext () [0x00023] in /Developer/MonoTouch/Source/mono/mcs/class/System.Core/System.Linq/Enumerable.cs:1157
at System.Collections.Generic.List`1[Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser].AddEnumerable (IEnumerable`1 enumerable) [0x00000] in <filename unknown>:0
at System.Collections.Generic.List`1[Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser]..ctor (IEnumerable`1 collection) [0x00000] in <filename unknown>:0
at System.Linq.Enumerable.ToArray[CsUser] (IEnumerable`1 source) [0x00000] in <filename unknown>:0
at System.Linq.QuickSort`1[Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser]..ctor (IEnumerable`1 source, System.Linq.SortContext`1 context) [0x00000] in <filename unknown>:0
at System.Linq.QuickSort`1+<Sort>c__Iterator2F[Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CsUser].MoveNext () [0x00000] in <filename unknown>:0
at System.Linq.Enumerable.Count[CsUser] (IEnumerable`1 source) [0x00000] in <filename unknown>:0
at CSMobile.Logic.Forms.Login_Dal.GetUsersSqlCount () [0x00000] in /Volumes/Mobile2011/Mobile 2011/trunk/WinCE/CSMobile/CSMobile.Logic/Forms/Login.Dal.cs:38
at CSMobile.Logic.Forms.Login_Logic.GetUsers () [0x0001f] in /Volumes/Mobile2011/Mobile 2011/trunk/WinCE/CSMobile/CSMobile.Logic/Forms/Login.Logic.cs:198
at CSMobile.Logic.Forms.Login_Logic.Anmelden2 (Int32 selectedProduct) [0x00050] in /Volumes/Mobile2011/Mobile 2011/trunk/WinCE/CSMobile/CSMobile.Logic/Forms/Login.Logic.cs:416
at CSMobile.UI.Login.Logic_LoginStepCompleted (Login_StepResult result) [0x0003e] in /Volumes/Mobile2011/Mobile 2011/trunk/IOS/CSMobile/CSMobile.UI/Forms/Login.cs:325
at CSMobile.Logic.Forms.Login_Logic.Anmelden1 () [0x00084] in /Volumes/Mobile2011/Mobile 2011/trunk/WinCE/CSMobile/CSMobile.Logic/Forms/Login.Logic.cs:364
at CSMobile.UI.Login.StartLogin () [0x00000] in /Volumes/Mobile2011/Mobile 2011/trunk/IOS/CSMobile/CSMobile.UI/Forms/Login.cs:75
at CSMobile.UI.Login.Pad_Start_TouchUpInside (MonoTouch.Foundation.NSObject sender) [0x00000] in /Volumes/Mobile2011/Mobile 2011/trunk/IOS/CSMobile/CSMobile.UI/Forms/Login.cs:235
at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00042] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:29
at MonoTouch.UIKit.UIApplication.Main (System.String[] args) [0x00000] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:34
at CSMobile.UI.Application.Main (System.String[] args) [0x0000a] in /Volumes/Mobile2011/Mobile 2011/trunk/IOS/CSMobile/CSMobile.UI/Main.cs:18
[ERROR] FATAL UNHANDLED EXCEPTION: System.ExecutionEngineException: Attempting to JIT compile method 'System.Linq.Enumerable:<ToLookup`2>m__5A<Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CeMitarb, System.Nullable`1<int>> (Genesis.DataAccess.Schema.Mobile.V1.Wrapper.CeMitarb)' while running with --aot-only.

Answer 1

I think this limitation here is actually due to Generic Virtual Methods - http://docs.xamarin.com/ios/about/limitations#Generic_Virtual_Methods
There's a discussion of a very similar problem on the mailing list:
http://monotouch.2284126.n4.nabble.com/LINQ-JIT-error-again-td3800970.html;cid=1338984263803-35#a3800169
It didn't sound like that thread found a solution
It might be worth contacting Xamarin support directly on this one. http://bugzilla.xamarin.com/

Answer 2

Generics are a bit weird on MonoTouch due to AOT compilation. A true runtime / JIT is disallowed in iOS, so it must compile everything ahead-of-time.
In this particular case, your method which returns IEnumerable<CsUser> is most likely the culprit. Generic interfaces cause problems. Try changing your return type to a List<CsUser> or any other concrete class that implements IEnumerable<CsUser>.

Answer 3

OrderBy is known to fail in this scenario. This appears to be fixed in MonoTouch version 2.10 but unfortunately if you're using an engine like Unity, that only ships with 2.6 currently (as of 4.3.x).
https://bugzilla.xamarin.com/show_bug.cgi?id=2155#c11

Answer 4

I don't know a convenient solution for Xamarin at the moment.
However there is such a solution for Unity 3D.
You can try LINQ to iOS. It's a custom implementation of LINQ to Objects extension methods that works on iOS without JIT-compile errors. If you're using Xamarin you may try to take .dll from LINQ to iOS and use it in your project. After all, Xamarin and Unity both use Mono compiler.