That's all fine and dandy but irrelevant since Crystal doesn't have a GIL (or, indeed, an interpreter). Threading does imply parallelism in this context.
Indeed, and there seems to have been some work done to great effect[0]. Unfortunately the corresponding branch is quite stale[1].
Anyway, my comment was more about the fact that the "Concurrency / Add multithreading support" section of the roadmap was quite unclear about parallelism. Mentioning MRI's GIL was merely an example as to why any kind of thread interlocking could turn things into non- (or very limited) parallelism, hence patagonia's question being quite legitimate.
