[straight-shoota]

concurrency != multi-threading.

Crystal's concurrency is based on fibers (green threads) which works very well even on a single thread (it scales to multiple threads, as well)

And for many use cases with high parallelization and little shared state (including web applications such as a search engine), multi-threading isn't necessary. Synchronization overhead is a serious performance killer. You can get much more performance out of running N processes with a single thread instead of a single process running N threads.

[zw963]

Hope a lot of people can see this, detailed explanation come from Crystal core developers.

because a lot of beginners complain that Crystal's fiber doesn't work on multiple cores/multiple threads and then give up using it, it's probably not as important as people think.

Even many beginners mistakenly believe that the Crystal language does not support the creation of operating system native Thread， this is a huge misunderstanding for Crystal.