Java - Base Six

Tungsten FSM: A lightweight Java finite state machine library

James Furness — Sun, 05 Dec 2010 18:36:00 +0000

I recently came across Tungsten FSM whilst looking for an off the shelf FSM implementation. Ideally I was looking for something which was a lightweight and no-frills but robust FSM implementation, and Tungsten FSM seemed to exactly fit the bill. All configuration is done in code, so no messing around with XML files, and the implementation itself is only a handful of classes with only one dependency (log4j).

All in all worked out very well, and it seems to do exactly what it promises. The support for sub-states is useful to cut down on config bloat by defining common transitions on a parent state.

If I were to nitpick it would have been nice to see generics used to avoid needing to cast the entities/events, however this would arguably bloat the Tungsten source somewhat. It would have also been nice to be able to specify an “ignore” type transition which could be specified on a parent state to ignore an event rather than having to define transitions on all sub states of the parent state for an event in order to ignore it and stay in the same state.

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Calculating floating point epsilon/precision in Java

James Furness — Thu, 24 Jun 2010 10:25:44 +0000

Floating point arithmetic/rounding can be somewhat painful, made worse by the fact that the epsilon (error) in the machine representation of floating point varies depending on the exponent (i.e. how large/small the number being represented is):

Normalized numbers when Base = 2, Precision = 3, Exponents = -1 to 2 [Goldberg91]

A very comprehensive paper (from which the above image is taken) is available here. In previous teams we have implemented our own functions to derive an approximation of the epsilon from the number to be represented, however I discovered recently to my surprise that such a function was added to Java in 1.5: Math.ulp!

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JMM Synopsis

James Furness — Tue, 15 Sep 2009 10:32:49 +0000

Useful synopsis of the Java Memory Model from Doug Lea – in particular the clearest explanation I have found so far of the meaning of “happens-before”, and some useful definitions which helped to get a concrete idea of the semantics around safe-publication of variables through Thread.start()…

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NonBlockingHashMap

James Furness — Mon, 15 Jun 2009 08:12:31 +0000

Just came across this, looks like it has been around on Sourceforge for a while as part of lib-high-scale. Designed for large numbers of CPUs (e.g. Azul hardware), but microbenchmarks claim a small improvement over ConcurrentHashMap even on 2 CPUs.

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