So I was wrote a function that read a InputStream into a
FileOutputStream.
I noticed (after my CPU fan kept turning on) that it was taking
upwards of 70% of my Athlon 64 X2 +5000!
Heres that version:
(defn read-bytes-to-file [istream filename]
(with-open [ostream (new FileOutputStream filename)]
(let [buffer (make-array (. Byte TYPE) 4096)]
(loop [b-read (. istream (read buffer))]
(if (neg? b-read)
nil
(do (.write ostream buffer 0 b-read)
(recur (.read istream))))))))
user> (time-test (read-bytes-to-file (.openStream (new URL "http://
imgs.xkcd.com/comics/google_trends.png")) "/dev/null"))
"Elapsed time: 1183.442361 msecs"
"Elapsed time: 533.216065 msecs"
"Elapsed time: 502.899459 msecs"
"Elapsed time: 499.715278 msecs"
"Elapsed time: 505.39608 msecs"
nil
This version is actually the result of me messing around with it for a
while (Trying Buffering and such).
Then I read a post here and tried this:
(defn read-bytes-to-file [istream filename]
(with-open [ostream (new FileOutputStream filename)]
(let [buffer (make-array (. Byte TYPE) 4096)]
(loop [b-read (. istream (read buffer))]
(if (pos? b-read)
(do (.write ostream buffer 0 b-read)
(recur (.read istream)))
nil)))))
and got this:
(time-test (read-bytes-to-file (.openStream (new URL "http://
imgs.xkcd.com/comics/google_trends.png")) "/dev/null"))
"Elapsed time: 423.394728 msecs"
"Elapsed time: 186.605035 msecs"
"Elapsed time: 201.295071 msecs"
"Elapsed time: 201.775338 msecs"
"Elapsed time: 197.739148 msecs"
nil
It also only uses up to 2 percent of the CPU. So I guess its really
important to make the then of an if the most likely case. Anybody know
why?
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