Comment by nsm
I’m confused about the assertion that green threads perform badly. 3 of the top platforms for high concurrency servers use or plan to use green threads (Go, Erlang, Java). My understanding was that green threads have limitations with C FFI which is why lower level languages don’t use them (Rust). Rust may also have performance concerns since it has other constraints to deal with.
Green threads have issues with C FFI mostly due to not being able to preempt execution, when the C thing is doing something that blocks. This is a problem when you have one global pool of threads that execute everything. To get around it you essentially need to set up a dedicated thread pool to handle those c calls.
Which may be fine - go doesn't let the user directly create thread pools directly but do create one under the hood for ffi interaction.