I was coming up with some performance tests for Clojure, going back
and forth between different JVM languages (JRuby, Scala) and mainly
looking at pure Java code. So far I have found that clojure is about
5-10 times as slow as comparable code in Clojure. Of course this is
before any optimizations.
Here is my question, do you have any code both Clojure and Java where
there is a one to one match between code where Clojure runs as fast as
Java. It could be anything.
Here is one example:
This is code from clojure/contrib to convert a list of data into a
frequency count map. Pretty standard stuff.
(defn frequencies
"Returns a map from distinct items in coll to the number of times
they appear."
[coll]
;;;;;;;;;
(reduce (fn [counts x]
(assoc counts x (inc (get counts x 0))))
{} coll))
(dotimes [x 4]
(println "i: " (int (Math/pow 10.0 x)))
(time
(dotimes [_ (int (Math/pow 10.0 x))]
(let [a (for [_ (range 1000)] (random-string 3))]
(frequencies a)))))
----------------------
public static Map frequencies(final List list) {
final Map map = new HashMap();
// Simple Box and then unbox the count as the value for this
map //
for (Iterator it = list.iterator(); it.hasNext(); ) {
final Object o = it.next();
final String s = o.toString();
Integer prev = (Integer) map.get(s);
if (prev == null) {
// Put a new value on th map
final Integer count = ONE;
map.put(s, count);
} else {
final Integer inc = new Integer(prev.intValue() + 1);
map.put(s, inc);
} // End of the if - else //
}
return map;
}
----------------------
Clojure Results (same machine 1.5 JDK)
i: 1
"Elapsed time: 51.657859 msecs"
i: 10
"Elapsed time: 212.568221 msecs"
i: 100
"Elapsed time: 1623.107702 msecs"
i: 1000
"Elapsed time: 16356.185166 msecs"
(used:2M/0M [2M,63M ])
Done
Performing simple garbage collection cooldown
(used:2M/0M [2M,63M ])
(used:2M/0M [2M,63M ])
-------------
Here are the Java results.
14.631606999999999 ms
4.828342999999999 ms
i: 10
Elapsed time: 9.803628 msecs
i: 100
Elapsed time: 97.562451 msecs
i: 1000
Elapsed time: 972.775771 msecs
(used:1M/0M [1M,63M ])
(used:1M/0M [1M,63M ])
(used:1M/0M [1M,63M ])
NOTE:!!! This is just one example. All my other examples, ended up
the same way. I hope you don't nitpick this one.
I know we should take performance tests with a grain a salt. But at
the same time, I feel we should at least try to measure the speed of
some of our code. I haven't found many speed tests out there on
clojure.
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