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Yeah, having each engine in its own process and doing IPC seemed like a huge ordeal that I wanted to avoid, but now I'm thinking it might not be so bad, and it would be easier and safer than fussing with classloaders. I brushed up on some RMI stuff last night, but even that requires some setup to get the RMI registry going and stuff, which I don't really want to force on people. I think just starting the separate processes with Runtime.exec and communicating with them over STDIN and STDOUT may be the simplest solution all around.