MonoTouch JIT Error in Release mode on Linq Method

Question

I currently have some code as shown below that uses Linq to organize some IEnumerables for me. When executing this code on the device in release mode (iOS 5.0.1, MonoTouch 5.0.1, Mono 2.10.6.1) I get the exception

Attempting to JIT compile method 'System.Linq.OrderedEnumerable`1:GetEnumerator()' while running with --aot-only.

The code that generates this error is

// List<IncidentDocument> documents is passed in
List<LibraryTableViewItemGroup> groups = new List<LibraryTableViewItemGroup>();
List<DocumentObjectType> categories = documents.Select(d=>d.Type).Distinct().OrderBy(s=>s.ToString()).ToList();
foreach(DocumentObjectType cat in categories)
{
    List<IncidentDocument> catDocs = documents.Where(d => d.Type == cat).OrderBy(d => d.Name).ToList();
    List<LibraryTableViewItem> catDocsTableItems = catDocs.ConvertAll(d => { return new LibraryTableViewItem{ Image = GetImageForDocument(d.Type), Title = d.Name, SubTitle = d.Description}; });
    LibraryTableViewItemGroup catGroup = new LibraryTableViewItemGroup{ Name = GetCatName(cat), Footer = null, Items = catDocsTableItems };
    groups.Add (catGroup);
}

This error doesn't happen in the simulator for Release|Debug configurations, or on the device for the Debug configuration. I've seen a couple of similar threads on SO here and here, but I'm not sure I understand how they apply to me on this particular issue.

It seems to me that I'm telling the compiler to AOT everything, so wouldn't it need to discover the types beforehand? I see the workarounds, but I fail to understand why they are necessary in Release/Device only. If I tell Linq to generate a list of a concrete type like .ToList<DocumentObjectType>() instead of .ToList() is taht a sufficient clue to the compiler to AOT those types properly? — pseabury
No, because the problem is IOrderedEnumerable<T>, not List<T>. Although I don't know how you can create an IOrderedEnumerable<DocumentObjectType> without orderby.. — TheNextman

poupou poupou · Accepted Answer · 2011-11-19T17:03:56

It could be a few things.

There are some limitations when using full AOT to build iOS applications, i.e. ensuring that nothing will be JITted at runtime (an Apple restriction). Each one is different even if the message looks identical (i.e. many causes will lead to this). However there are generally easy workarounds we can suggest for them;
It could also be a (known) regression in 5.0.1 (which is fixed in 5.0.2). This produced a few extra AOT failures that are normally not issues (or already fixed issues).

I suggest you to update to MonoTouch 5.0.2 to see if it compiles correctly your application. If not then please fill a bug report on http;//bugzilla.xamarin.com and include a small, self-contained, test case to duplicate the issue (the above is not complete enough). It seems an interesting test case if it works when debugging is enabled.

MonoTouch JIT Error in Release mode on Linq Method

1 Answers