There are none, or you're not aware of their existence?

There are no production implementations of GC algorithms that don't stop the world at all. I know this because I have some expertise in GC algorithms.

I'm curious why you don't consider C4 to be production grade

Azul C4 is not a pauseless GC. In the documentation it says "C4 uses a 4-stage concurrent execution mechanism that eliminates almost all stop-the-world pauses."

Except the documentation says

> C4 differentiates itself from other generational garbage collectors by supporting simultaneous-generational con- currency: the different generations are collected using concurrent (non stop-the-world) mechanisms

It doesn't matter at all. C4 uses STW.

I wish I could have learned more from this interaction than it doesn't matter.

I have heard (and from when I investigated) erlangs GC is 'dont stop the world'.

Maybe my definition is bad though.