JRuby doesn't have a GIL to begin with so there's no requirement to use multiprocessing to host Rails apps etc. They're an improvement over a single GIL but no

JRuby doesn't have a GIL to begin with so there's no requirement to use multiprocessing to host Rails apps etc. They're an improvement over a single GIL but not by much. IIUC, they're like Racket's Places: a complete duplication of the VM but sharing an address space. The basic implementation doesn't really save much memory but it's a bit more convenient. There's been a couple of attempts to implement subinterpreters for CRuby too.