94.574 Elements of Computer Systems

SCE 574

186

Co-routines (cont.)

äA routine gives up control explicitly by branching to another routine

äIn the example:

äEach routine is only aware of one entry point for each other routine

äThere could be more

äThe scheduler decides on the order of execution

äCould describe the scheduler using a finite state machine/state transition diagram

äThese details could be hard-coded into the routines

äAdvantage: faster execution

äDisadvantage: more difficult to maintain

äCommunication can take place via variables in a data segment

äCo-routines of this nature are usually written in assembler

äNeed access to registers to save context and do branching

äA single stack used in a high level language would get in the way

äWhy? We have not explicitly distinguished threads of control