On Tue, Dec 28, 2010 at 8:57 PM, Mark Engelberg <mark.engelb...@gmail.com>wrote:
> Just for fun, I was curious to see what it would be like,
> performance-wise, to simulate a synchronized mutable hash map by
> putting a clojure hash map inside an atom, and making this accessible
> to Java code via the map interface.
>
;; ~50ms-60ms
(dotimes [_ 10]
(let [m (atom {})
r (range 1e5)]
(time
(doseq [i r]
(swap! m assoc i 2)))))
;; same as above
(dotimes [_ 10]
(let [m {}
r (range 1e5)]
(time
(loop [m m r r]
(if (nil? r)
m
(recur (assoc m (first r) 2) (next r)))))))
(def ^java.util.Map j (. java.util.Collections synchronizedMap
(java.util.HashMap.)))
;; ~10ms
(dotimes [_ 10]
(time (doseq [i (range 1e5)] (.put j i 2))))
So it's about 5X-6X slower for 1e5. But it looks to me there's no overhead
from atom operations.
I note that for 1e3 keys the difference is around 2X.
Of course this isn't much of a comparison IMO because the Java HashMap isn't
persistent. The Clojure version can add many keys as an atomic operation.
Much more useful if you're using a map as some kind of in-memory data store.
David
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