You could likely use System/identityHashCode to count the similarity of
objects all the objects.
I created a small function that only honors the "clojure-visible"
structure, and exposes every item in a tree structure (apart from the
arrays in PersistentVectors and some PersistentMaps)
(defn steam-roller [l]
"gives a representation of all object pointers in a
nested structure by both adding pointers to everything seqable
as well as its contents
it also takes out keys and vals of maps, as well as the whole map"
(let [l [l]]
(loop [l1 l l2 '()]
(cond
(sequential? (first l1)) (recur (concat (first l1) (rest l1)) (cons
(first l1) l2))
(map? (first l1)) (recur (concat (keys (first l1)) (vals (first l1))
(rest l1)) (cons (first l1) l2))
(empty? l1) (reverse l2)
:else (recur (rest l1) (cons (first l1) l2))))))
(inspired by slovic's version of flatten at
http://clojuredocs.org/clojure_core/clojure.core/flatten)
Example output is:
(steam-roller *[:a :b {:c 2 3 4}]*)
-> (*[:a :b {:c 2, 3 4}]* :a :b {:c 2, 3 4} :c 3 2 4)
You could then make some trivial statistics collection like
(map #(System/identityHashCode %) (steam-roller {1 2 3 4}))
-> (359344022 504432400 1778018115 1172818142 256714182)
where (set) gives the unique HashCodes.
The reasoning behind not taking out mapEntries of maps, but just the keys
and vals is that maps usually is k-v-pairs in an Object-array or a shallow
tree of those Objectarrays.
This does *not* take care about either implementation details in either
PersistentVector or rrb-vector. I guess one could use
https://github.com/arohner/clj-wallhack or https://github.com/zcaudate/iroh
to walk around inside the inners of PersistentVector and rrb-vector.
The conclusion of this is I think the easiest way to make this work is to
just run the algorithm in both versions and watch the object allocation
statistics closely in VisualVM or similar. My intuition is that the there
will be a lot of copied arrays, but that's quite quick (not as quick as
shuffling longs with sun.misc.Unsafe, though).
/Linus
2014-08-11 14:56 GMT+02:00 Paul Butcher <p...@paulbutcher.com>:
> Is there any way to benchmark the degree of structural sharing achieved by
> a Clojure algorithm? I'm evaluating two different implementations of an
> algorithm, one which uses zippers and one which uses rrb-vector. It would
> be great if there were some way to quantify the degree to which they both
> achieved (or didn't) structural sharing.
>
> --
> paul.butcher->msgCount++
>
> Silverstone, Brands Hatch, Donington Park...
> Who says I have a one track mind?
>
> http://www.paulbutcher.com/
> LinkedIn: http://www.linkedin.com/in/paulbutcher
> Skype: paulrabutcher
>
> Author of Seven Concurrency Models in Seven Weeks: When Threads Unravel
> http://pragprog.com/book/pb7con
>
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