Before posting, I had repeated this multiple times, running this code inside a sandbox.
After seeing your reply, I tried but couldn't repro it at the command line. I could still repro it in the sandbox. But with a fresh sandbox, now I can't repro it anymore. I guess some mysterious bit of state was causing this (but only for the first call to vector-length??). I know the rule -- only do serious profiling at the command line. In this case I didn't expect it would matter. I figured "some number vs. some smaller number" could be due to environment overhead, but not "some number vs. 0". However I was wrong. On Sat, Mar 8, 2014 at 1:57 PM, Laurent <laurent.ors...@gmail.com> wrote: > I get : > >> (let ((v (time (make-vector 50000000 0)))) > (time (vector-length v)) > (time (vector-length v)) > (time (vector-length v)) > (void)) > cpu time: 188 real time: 191 gc time: 12 > > cpu time: 0 real time: 0 gc time: 0 > cpu time: 0 real time: 0 gc time: 0 > cpu time: 0 real time: 0 gc time: 0 > > Which seems consistent to me. > > Are you trying on the command line? > > Laurent > > > On Sat, Mar 8, 2014 at 7:35 PM, Greg Hendershott <greghendersh...@gmail.com> > wrote: >> >> As for length: >> >> (for ([i 3]) (collect-garbage)) >> (let ((ls (time (make-list 50000000 0)))) >> (time (length ls)) >> (time (length ls)) >> (time (length ls)) >> (void)) >> >> It's what I would expect: >> >> cpu time: 6733 real time: 6744 gc time: 6419 >> cpu time: 141 real time: 141 gc time: 0 >> cpu time: 145 real time: 145 gc time: 0 >> cpu time: 142 real time: 142 gc time: 0 >> >> - - - - - >> >> Next, thinking about 50000000 elements made me think about vectors, >> vector? and vector-length. >> >> This: >> >> (for ([i 3]) (collect-garbage)) >> (let ((v (time (make-vector 50000000 0)))) >> (time (vector-length v)) >> (time (vector-length v)) >> (time (vector-length v)) >> (void)) >> >> prints: >> >> cpu time: 182 real time: 183 gc time: 1 >> cpu time: 315 real time: 315 gc time: 314 >> cpu time: 0 real time: 0 gc time: 0 >> cpu time: 0 real time: 0 gc time: 0 >> >> Huh? The first call to vector-length takes even longer than making >> the vector (and, seems to be almost entirely gc). >> >> I would have guessed that make-vector would create a structure with >> the length already stored in it, and all vector-length calls would be >> essentially 0. >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users > > ____________________ Racket Users list: http://lists.racket-lang.org/users
