Deadlock issue

I logged an issue on Codeplex (#6449) about the previous deadlock bug I
encountered, and I have come up with a patch which should fix the issue,
which I’ve submitted as a pull request:

To explain the patch:

I did some more research, and it appears as though there was already a
lock order implicitly specified when locking both ClassHierarchyLock and
ModuleCacheLock - the hierarchy lock must come first: (refer
RubyContext.cs line 1051)

I then traced through all the Locks in RubyContext - The majority are
simple operations and don’t require any modification, so I added
I followed the usage of ModuleCacheLock, and made sure the hierarchy
was acquired first if it might need to be acquired in a nested call.

  • This amounts to a couple of calls to GetOrCreateClassNoLock, which
    requires both the module cache lock and the hierarchy lock

Also added a comment above ModuleCacheLock explaining the lock order,
a RequiresClassHierarchyLock to GetOrCreateClassNoLock to clarify these

I’ve run some heavily multithreaded test code I have and the changes
to make no appreciable difference to the performance or multi threading
capability of IronRuby