Green threads emulate multithreaded environments without relying on any native OS abilities, and they are managed in user space instead of kernel space, enabling them to work in environments that do not have native thread support.
[5] To avoid that problem, green threads must use non-blocking I/O or asynchronous I/O operations, although the increased complexity on the user side can be reduced if the virtual machine implementing the green threads spawns specific I/O processes (hidden to the user) for each I/O operation.
[citation needed] In the case of GHC Haskell, a context switch occurs at the first allocation after a configurable timeout.
[citation needed] Most Smalltalk virtual machines do not count evaluation steps; however, the VM can still preempt the executing thread on external signals (such as expiring timers, or I/O becoming available).
Unlike most green thread implementations, QKS also supports preventing priority inversion.