[e-lang] What is defensive consistency?

[Tyler Close]

On 10/31/07, David Wagner <daw at cs.berkeley.edu> wrote:
> Last question: Can anyone suggest an example of a defensively consistent
> component that helps illustrate the concept?  MarkM's gives an example
> of a Counter that has an increment() method and nothing else, but I
> yearned for something that exposed some non-trivial challenges/issues.
> Can anyone give a slightly less trivial example that might help me to
> understand the concept of defensive consistency with a concrete example?

I think the observable, mutable slot is a useful example. There's a
write-up, adapted from MarkM's thesis, at:

http://waterken.sourceforge.net/javadoc/org/ref_send/promise/eventual/Eventual.html

At the top of the page is a version that exhibits all the failure
modes. Further down is a version that is defensively consistent:

http://waterken.sourceforge.net/javadoc/org/ref_send/promise/eventual/Eventual.html#_(T)

I think all the issues raised in your email can be explored using this example.

--Tyler

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