Question

What is the best way to understand the Java HotSpot VM? And if I want to make modifications to the source code and add my own features, what would be the best development environment (does ctags work well with the large code base, or do I need a full-blown IDE)?

Answer 1

I doubt that you would want to dive into the Hotspot code-base… I’m copying parts of my answer on from this question:

• Which JVM to choose for GC hacking?

I think the Maxine Research VM from Oracle Labs would be a good starting point. Here’s a quote from the first page of their wiki:

Project Overview

In this era of modern, managed languages we demand ever more from our virtual machines: better performance, more scalability, and support for the latest new languages. Research and experimentation is essential but no longer practical in the context of mature, complex, production VMs written in multiple languages.

The Maxine VM is a next generation platform that establishes a new standard of productivity in this area of research. It is written entirely in Java, completely compatible with modern Java IDEs and the standard JDK, features a modular architecture that permits alternate implementations of subsystems such as GC and compilation to be plugged in, and is accompanied by a dedicated development tool (the Maxine Inspector) for debugging and visualizing nearly every aspect of the VM’s runtime state.

Here’s an excelent video demonstrating its memory monitoring utilities:

• Introduction to the Maxine Inspector