Comment by falserum
18 hours ago
Green threads don’t allocate stack frames and do not require such a massive context switch, which in turn allows for many more threads.
18 hours ago
Green threads don’t allocate stack frames and do not require such a massive context switch, which in turn allows for many more threads.
But if you happen to call a blocking syscall everything breaks.
That is not true of preemptive green threading systems. Go/Erlang/Haskell all run native foreign code on its own threads, and manage all internal I/O with async schedulers that never block. They also preempt user code in tight loops.
Those are the only mature languages that have all of these features.
Not sure if purposefully but you left out java. It doesn't preempt a CPU hot loop, but arguably you don't really want to disturb the CPU there / the whole "green thread" model doesn't make much sense with that kind of workload. That's why you have ordinary threads as well.
That's why higher level languages are in an advantage. E.g. in java - outside of FFI - syscalls are basically "only within" standard library functions. So it was possible to make them virtual thread aware, e.g. park a virt thread, use something like io uring for the actual IO call on the JVM level and resume it when it returns, doing work on another virt thread in the meanwhile.