A timer wheel implementation with BORDEAUX-THREADS backend.

timer-wheel

# 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](https://sourceforge.net/p/sbcl/mailman/message/35583449/) 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
```lisp
(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?


timer-wheel

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