[IronPython] parallel importing

[Kamil Dworakowski]

Importing time is such a pain that I wanted to do it in parallel on
many threads. I figured that if the modules where imported in such a
way that:

no two threads import the same module at the same time

everything would be fine. To ensure that condition, it is enough to
build a dependency graph and import based on that.

I did it: Resolver One start up time improved by 20% on a two-core
machine. But it crashes, surprisingly on single core machines it is
more often (6 crashes on 200 starts).

So far I have identified two causes for crashes:

1. One thread imports a module with class B inside while another is
importing a module with class C inside. If B and C are subclasses of
A, it can result in IndexOutOfRangeException being raised, when, under
the hood, IronPython.Runtime.Types.DynamicType.AddSubclass is being
executed.

2. Attributes on .NET modules are loaded lazily, so importing
namespaces only is not enough. Attribute getting from reflected
packages is not thread safe. Looks like I would have to import every
class explicitly (would that be enough?).

Second cause would be pretty easy to address, but I'm not so sure
about the first one. Are there any more potential points of problems?
I am beginning to think I was to optimistic about all of this
importing on multiple cores, but if these are the only ones it could
probably be still fixed.

If anyone is interested the code for it is on github:
http://github.com/luntain/ipy-parallel-import.

--
Kamil Dworakowski
Resolver Systems Ltd.