Clojure: input-stream slower than reader

Question

I'm trying to read bytes from input-stream and it much slower than reading chars with reader. I can't figure out why it is so. Look at the test:

(defn r1
  [input]
  (loop []
    (when-not (= -1 (.read ^java.io.InputStream input))
      (recur))))

(defn r2
  [input]
  (loop []
    (when-not (.read input)
      (recur))))

(dotimes [_ 10] 
   (time (with-open [is (clojure.java.io/input-stream "15mb.log")]
     (r1 is))))

"Elapsed time: 111.608991 msecs"
"Elapsed time: 95.45663 msecs"
"Elapsed time: 148.789867 msecs"
"Elapsed time: 97.580527 msecs"
"Elapsed time: 113.093759 msecs"
"Elapsed time: 108.306019 msecs"
"Elapsed time: 107.71069 msecs"
"Elapsed time: 104.833343 msecs"
"Elapsed time: 174.701027 msecs"
"Elapsed time: 141.969629 msecs"

(dotimes [_ 10]
   (time (with-open [r (clojure.java.io/reader "15mb.log")]
      (r2 r))))

"Elapsed time: 0.635769 msecs"
"Elapsed time: 0.422315 msecs"
"Elapsed time: 0.355953 msecs"
"Elapsed time: 0.336128 msecs"
"Elapsed time: 0.333523 msecs"
"Elapsed time: 0.339613 msecs"
"Elapsed time: 0.329693 msecs"
"Elapsed time: 0.234213 msecs"
"Elapsed time: 0.209742 msecs"
"Elapsed time: 0.199334 msecs"

As far as I know clojure.java.io/input-stream uses BufferedInputStream and clojure.java.io/reader uses BufferedReader so there no reason to so dramatical difference in speed. Do I miss something?

Are you sure your r2 is correct? Didn't you use .readLine there? (testing if the result is falsy instead of comparing it to -1 would indicate it) — Piotrek Bzdyl
– Piotrek Bzdyl, Commented Mar 16, 2017 at 16:30

Josh · Accepted Answer · 2017-03-16 22:08:04Z

1

Your test is flawed. Both BufferedReader and BufferedInputStream return -1 at the end of the stream. So, your test for r2 should also be (when-not (= -1 (.read ....

While the below method of testing is not accurate down to very small millisecond levels, it's accurate enough for this test, and a test using the very good criterium benchmark library for clojure yields similar results. Posting the test again more compactly, for easy copy/paste:

(let [testfile "zerofile"]    ; $ dd if=/dev/zero of=zerofile bs=1k count=1k
  (map (fn [func label]
         (println label)
         (dotimes [_ 3]
           (time (with-open [data (func testfile)]
                   (while (not= -1 (.read data)))))))
    [clojure.java.io/input-stream,  clojure.java.io/reader]
    ["Input Stream:" "\nReader:"]))

One result:

Input Stream:
"Elapsed time: 624.01494 msecs"
"Elapsed time: 650.407183 msecs"
"Elapsed time: 627.244097 msecs"

Reader:
"Elapsed time: 706.776733 msecs"
"Elapsed time: 691.887275 msecs"
"Elapsed time: 703.918226 msecs"

edited Mar 16, 2017 at 22:08

answered Mar 16, 2017 at 21:47

Josh

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1 Comment

Eugene Aksenov Over a year ago

Thanks for your help, I see now. I'm exit too soon with a reader in my example.

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