Appendix B:

Anatomy of a context switch between two user-level strands

• Suppose a user-level strand is executing in domain a.
• Clocktick event occurs. Suspended state pointer ( S) points to this state ( X). When event handling is finished, ^S will be resumed.
• The handler for Clocktick is a piece of the global scheduler that has registered to be executed in its own domain g.
• Scheduler raises Stop. Stop handler executes in its registered domain a, and saves away as much state as it needs.
• Back to the scheduler in domain g. Scheduler changes the saved state pointer S to point to a context that will execute an idle loop.
• Scheduler changes the current domain to destination domain b.
• Scheduler raises Run.
• The Run handler should now change S to something that will resume a user-level computation.