Thanks guys. I had a feeling that it wasn't doing the calculation twice the way it was coded in the book.
Ryan On Tuesday, July 23, 2013 11:23:21 AM UTC-4, Lars Nilsson wrote: > > On Tue, Jul 23, 2013 at 11:12 AM, Baishampayan Ghose > <b.g...@gmail.com<javascript:>> > wrote: > > It's definitely got to do with the code, the right way to test it out > > will be to wrap the form in a function and then calling it twice. Like > > so - > > > > (time > > (let [x (fn [] (Thread/sleep 2000) > > (+ 1 1))] > > [(x) (x)])) > > ;=> "Elapsed time: 4002.0 msecs" > > ;=> [2 2] > > > > Hope that helps. > > > > Regards, > > BG > > > > > > On Tue, Jul 23, 2013 at 8:34 PM, Ryan Moore > > <nicla...@gmail.com<javascript:>> > wrote: > >> There is an example in the book The Joy of Clojure on p.262 that uses > >> futures that I evaluated in the REPL. > >> > >> user> (time > >> (let [x (future (do (Thread/sleep 2000) > >> (+ 1 1)))] > >> [@x @x])) > >> "Elapsed time: 2000.809 msecs" > >> [2 2] > >> > >> I figured that taking out the future would cause the execution to take > twice > >> as long, however, when I try this: > >> > >> user> (time > >> (let [x (do (Thread/sleep 2000) > >> (+ 1 1))] > >> [x x])) > >> "Elapsed time: 2000.512 msecs" > >> [2 2] > >> > >> as you see it takes about the same amount of time. Does this have > something > >> to do with the REPL evaluating things or maybe the newer version of > Clojure > >> handles things differently from the Joy of Clojure book? > > Can also show the difference using two different vars > > (time (let [x (future (do (Thread/sleep 2000) (+ 1 1))) > y (future (do (Thread/sleep 3000) (+ 2 2)))] > [@x @y])) > > "Elapsed time: 3003.802 msecs" > [2 4] > > (time (let [x (do (Thread/sleep 2000) (+ 1 1)) > y (do (Thread/sleep 3000) (+ 2 2))] > [x y])) > > "Elapsed time: 5003.049 msecs" > [2 4] > > Basically, [x x] doesn't do the evaluation, it happens in the let once > for x. For [@x @x] the thread is kicked off once to do the > computation, and the first @x waits for the result (if not already > available) while the second @x uses the cached value. > > In my modified version, the second case the two Thread/sleep happens > in sequence, while in the first they take place in parallel thanks to > the futures. > > Lars Nilsson > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
