timer-wheel

2017-02-27

Timer Wheel

A portable Common Lisp timer wheel implementation. A timer wheel provides an efficient mechanism to implement tick-based timer routines. The portable part of this is the backend using Boreaux Threads to run a background thread operating the wheel.

Note that this package uses the internal-real-time to manage inter-tick timing intervals. Thus the correctness of the interval depends on how the specific lisp implementation implements internal-real-time. For instance, SBCL currently uses gettimeofday internally which means that a leap-second can stop time.

References

For the original reference I used, see "Real-Time Embedded Systems" by Xiaocong Fan, chapter 22.3. For some background on timers in Linux - http://www.elinux.org/Kernel_Timer_Systems - https://lkml.org/lkml/2005/10/19/46.

Example

(asdf:load-system :timer-wheel.examples)

;; Increment and print a counter value every tick with two different counters.
;; A third counter triggers the completion of the test.
(tw.examples:test 100 1500)

Testing

I've tested on Windows with SBCL 1.3 and CCL 1.11. I could get a timer wheel running with a resolution of 20 milliseconds without overruns (Nothing else going on). If you start loading up the garbage collector, I'm guessing that you'll start getting overruns. Test to determine what works.

TODO

  • Add a hierarchical timer wheel
  • Add OS specific timer back-ends?
  • HW timer backends?
Author
Nick Patrick <npatrick04@gmail.com>
License
MIT