how to build an object graph

After reading the article (Jeffrey's) about GC, I wonder how to build
a object graph to see what object is still alive and if so which
object is referring to them.

This is also important in practice. Since in a application where large
scale computation is going on, it's important to know which object are
kept alive incidently.

I've seen CLR profiler. But I wonder if I can build something myself
simular.