Comment by sczi

In ruby async is based on stackful fibers. With https://github.com/socketry/async-debug you can see a tree of all fibers with their full call stack. It also avoids the problem people talk about in this thread with go of passing a context parameter everywhere for cancellation as you can kill or raise any exception inside another fiber. I haven't used them but PHP fibers are also supposedly stackful. And Java and every JVM language has them since project loom in JDK 21.