In theory, every runtime (including JVM or even C!) implementation could be implemented with arbitrary user-space preemption, but it’s rather expensive, incurs

In theory, every runtime (including JVM or even C!) implementation could be implemented with arbitrary user-space preemption, but it’s rather expensive, incurs a lot of overhead. So, languages/platforms that (to some degree) optimize for performance (definitely C, but also Golang, JVM) avoid that. In particular, tight loops suffer - to support preemption, basically in every loop you need an extra condition, to check whether enough time has passes for the task to be interrupted. This turns out to be expensive enough that basically your language is useless for any kind of mathematical computations (all vector & matrix math and a lot of statistics is full of loops within loops). Golang in particular dealt with this issue extensively, not just because of starvation, but also because of GC - in order to enable garbage collection of global objects, all threads need to be paused and their local variables & stacks snapshoted. Doing that efficiently is hard. I think they were trying to make threads arbitrarily preemptable with OS signals, but that requires extreme care with implementation (you need to know where local variables are stored at every instruction!) and is not portable (no signals on Windows). E.g. https://github.com/golang/proposal/blob/master/design/24543-non-cooperative-preemption.md https://github.com/golang/proposal/blob/master/design/24543-...