Yes, "pauseless" is another keyword I forgot to mention. Azul uses a read barrier which I guess makes it so slow that noone uses it (and the same ideas haven't

Yes, "pauseless" is another keyword I forgot to mention. Azul uses a read barrier which I guess makes it so slow that noone uses it (and the same ideas haven't made their way into JDK collectors). The previous version required hardware-supported read barrier, now AFAIK they only require a Linux kernel extension.