1. A method comprising: creating a persistent user-level thread to run on an operating-system-sequestered sequencer independently of context switch activities on an operating-system-scheduled thread running on an operating-system-visible sequencer, wherein the persistent user-level thread continues execution when the operating-system-scheduled thread is context switched; suspending running of the persistent user-level thread when the persistent user-level thread encounters an event to be handled by an operating system; and communicating to another operating-system-visible sequencer a control-transfer instruction, and executing the control-transfer instruction at a privileged level.