[kevinpet]

I've never heard of a JVM that uses this kind of GC. As far as I know, every Sun JVM has used explicit "this is a pointer" to identify things for GC.

[r00tbeer]

Ah, you're right. Its only the thread stacks that were conservatively scanned, not all of memory (see "Mostly Accurate Stack Scanning" for some indirect evidence of such). Its not clear to me if modern JVMs are still conservatively scanning stacks or not. But clearly its much less of a problem than conservatively scanning all of memory.