dll - (Windows) How to make auto-update function for plugin?

Question

I have a question. I'm writing a plugin (.dll) for an application (.exe). And I want to code auto-update function for my plugin but I catched an issue, it could not apply. Because my plugin has loaded while application is running, in run-time it cannot replace. It just apply until application has exited. So, how can I do it?

This is my code: http://codepad.org/4a22ccMa

Thanks!

Answer 1

^{(this answers the original question, which has been edited to something completely different)}

It depends upon the operating system (which I guess might be Windows, since you speak of DLLs; on Linux you have shared objects (in ELF) with a different semantics). Read Levine's book Linkers and Loaders.

You might read more about Dynamic Software Updates. This is a entire research subject with a lot of scientific literature about it. Read e.g. the paper about Kitsune: Efficient, General-purpose Dynamic Software Updating for C (at least to understand several issues in your question).

On Linux, you could rename(2) the old .so and dlopen(3) the new one (and probably dlclose the older one, but you should do that later, when no active call frame on the call stack points into the old plugin), and my manydl.c example shows that you practically can dlopen a big lot (more than a million in practice) of shared objects.

On Windows (which I don't know) you probably need to dynamically load the new version of the plugin in a different file path. Probably, restarting your program after a plugin update should make things much easier.

^{(if you can afford that, switching to Linux might be very helpful, because I guess that it is much easier)}

Notice that in some languages (and some of their implementations) replacing some code is much easier than in C or C++ on Windows. I guess that in CLR (managed code, e.g. in C#) or in a JVM (e.g. in Java, Scala, Clojure) it should be easier. And in Common Lisp (at least with SBCL) it is quite easy (in particular since Common Lisp is an homoiconic language).

Take care of the continuation, i.e. of the call stack. You'll understand that your question (also related to orthogonal persistence & application checkpointing) is much deeper and more difficult than you have imagined. And upgrading classes and their instances is also very difficult.