Question

I’m implementing a compacting garbage collector for my own personal use in C++0x, and I’ve got a question. Obviously the mechanics of the collector depend upon moving objects, and I’ve been wondering how to implement this in terms of the smart pointer types that point to it. I’ve been thinking about either pointer-to-pointer in the pointer type itself, or, the collector maintains a list of pointers that point to each object so that they can be modified, removing the need for a double de-ref when accessing the pointer but adding some extra overhead during collection and additional memory overhead. What’s the best way to go here?

Edit: My primary concern is for speedy allocation and access. I’m not concerned with particularly efficient collections or other maintenance, because that’s not really what the GC is intended for.

Answer 1

This is a pretty straight-forward question so here’s a straight-forward answer:

Mark-and-sweep (and occasionally mark-and-compact to avoid heap fragmentation) is the fastest when it comes to allocation and access (avoiding double de-refs). It’s also very easy to implement. Since you’re not worried about collection performance impact (mark-and-sweep tends to freeze up the process in a nondeterministically), this should be the way to go.

Implementation details found at:

• http://www.brpreiss.com/books/opus5/html/page424.html#secgarbagemarksweep
• http://www.brpreiss.com/books/opus5/html/page428.html