As I mentioned in my previous post, online resources on Hosting are pretty scarce.
Also, writing an Host for the CLR requires some in-depth knowledge of topics you do not usually see in your day-to-day programming, like for example IO completion ports. Same for AppDomains: there is plenty of documentation and resources compared to Hosting, but still some more advanced feature, and the underlying mechanisms (how does it work? How does a thread interact and knows of AppDomains?) are not something you can find in a forum.
Luckily, I have been coding for enough time to have a programming library at home. Also, I have always been the kind of guy that wants to know not only how to use stuff, but how they really work, so I had plenty of books on how the CLR (and Windows) work at a low level. All the books I am going to list were already in my library!
The first one, a mandatory read, THE book on hosting the CLR:
Then, a couple of books from Richter:
The first one is very famous. I have the third edition (in Italian! :) ) which used to be titled "Advanced Windows". It is THE reference for the Win32 API.
If you go anywhere near CreateProcess and CreateThread, you need to have and read this book.
The second one has a title which is a bit misleading. It is acutally a "part 2" for the first one, focused on highly threaded, concurrent applications. It is the best explanation I have ever read of APCs and IO Completion Ports.
A couple of very good books on the CLR to understand Type Loading and AppDomains.
A "softer" read before digging into...
...the Internals. You need to know what a TEB is and how it works when you are chasing Threads as they cross AppDomains.
And you need all the insider knowledge you may get, if you need to debug cross-thread, managed-unmanaged transitions. And bugs spanning over asynchronous calls.
My edition of the first book is actually called "Inside Windows NT". It is the second edition of the same book, which described the internals of NT3.1 (which was, despite the name, the first Windows running on the NT kernel), and was originally authored by Helen Custer. Helen worked closely with Dave Cutler's original NT team. My edition covers NT4, but it is still valid today. Actually, it is kind of fun to see how things evolved over the years: you can really see the evolution, how things changed with the transition from 32 to 64 bits (which my edition already covers, NT4 used to run on 64 bit Alphas), and how they changed it for security reasons. But the foundations and concepts are there: evolution, not revolution.
And finally two books that really helped me while writing replacements for the ITaks API. The first one to tell me how it should work, the second one telling me how to look inside the SSLCI for the relevant parts (how and when the Hosting code is called).
Of course, I did not read all these books before setting to work! But I have read them over the years, and having them in my bookshelf provided a quick and valuable reference during the development of my host for Pumpkin.
This is one of the (few) times when I'm grateful to have learned to program "before google", in the late '90/early '00. Reading a book was the only way to learn. It was slow, but it really fixed the concepts in my mind.
Or maybe I was just younger :)