[rbehrends]

> Jikes RVM

The Jikes RVM is designed for research, not production. It's pretty impressive, but (inter alia) does not implement all of Java and does not support as many platforms.

> What's keeping this kind of GC technology back from the mainstream?

The fact that successful commercialization is possible; the GC tech that you see in Metronome and C4 is seriously non-trivial and not easy to reproduce unless you spend money on it; and it's also technology that businesses are willing to pay for.

At the same time, only a minority of open source use cases really require this kind of hard real-time GC, so there's little pressure to create an open source equivalent. Shenandoah is the one open source GC that does try to compete in this space, and it is trading away some performance for getting ultra-low pause times.

I'll add that this is difficult only because of concurrency and arbitrary sharing of data between threads. If you have one heap per thread, then it becomes much, much easier (and is a solved problem if soft real-time is all you need).