Thanks Carl and Robby for the explanations. I'm learning a great deal. I'm working with Tim Brown to learn how to use places.
-Joe On Thu, Jul 25, 2013 at 11:36 PM, Carl Eastlund <c...@ccs.neu.edu> wrote: > Joe, > > There are multiple concurrency and parallelism tools in Racket. If you > want concurrency but aren't concerned about parallelism, there are software > threads in Racket that will all run in the same OS thread ( > http://docs.racket-lang.org/reference/threads.html). If you want a tool > that supports both concurrency and parallelism, there are places, which > each run in a separate OS thread but have limited communication with each > other (http://docs.racket-lang.org/reference/places.html). What you're > using, futures, are a mechanism for parallelism without concurrency -- they > simulate deterministic, sequential behavior by only running in parallel as > long as known-pure operations are used, which is why so many operations > cause them to stop running in parallel ( > http://docs.racket-lang.org/reference/futures.html). > > Racket does not currently have what many other languages do, which is a > thread library that uses native OS threads with shared memory. As I > understand the issue, we have avoided that primarily because it complicates > the garbage collector's job, and often requires a "stop the world" approach > to garbage collection. Hopefully one of the options above will suffice for > your project. > > Carl Eastlund > > On Fri, Jul 26, 2013 at 12:43 AM, Joe Gilray <jgil...@gmail.com> wrote: > >> Hi Robby, >> >> Please pardon my ignorance, but is there an easy to use thread library >> with Racket? I've used threads in other environments and I don't recall so >> many restrictions. >> >> For example, how would you do something like a %-done meter if you have >> very limited ability to instrument the code you are metering? >> >> Thanks, >> -Joe >> >> >> On Thu, Jul 25, 2013 at 5:40 PM, Robby Findler < >> ro...@eecs.northwestern.edu> wrote: >> >>> hashes are definitely not future-safe, unfortunately. >>> >>> Robby >>> >>> >>> On Thu, Jul 25, 2013 at 6:50 PM, Joe Gilray <jgil...@gmail.com> wrote: >>> >>>> Here is an update: >>>> >>>> I rewrote gcd and used a hash-table for the squares check. The >>>> hash-table change sped up the sequential code about 10x! Then I tried >>>> using future / touch and it seems to improve the performance a little, but >>>> there is quite a bit of blocking (on >= and hash-ref) still. >>>> >>>> New code below. >>>> >>>> -Joe >>>> >>>> ; function that searches for progressive numbers for a given range of b >>>> values >>>> (define (find-progressive-num2 b-start b-end b-incr lim ht) >>>> (define (mgcd a b) (if (= b 0) a (mgcd b (modulo a b)))) >>>> (for/sum ([b (in-range b-start b-end b-incr)]) >>>> (let loopa ([a (add1 b)] [suma 0]) >>>> (cond >>>> [(> (mgcd a b) 1) (loopa (add1 a) suma)] >>>> [(>= (* a a a b) lim) suma] >>>> [else >>>> (let loopc ([c 1] [sumc 0]) >>>> (define n (+ (* a a a c c b) (* c b b))) >>>> (cond >>>> [(>= n lim) (loopa (add1 a) (+ suma sumc))] >>>> [(hash-has-key? ht n) (loopc (add1 c) (+ sumc n))] >>>> [else (loopc (add1 c) sumc)]))])))) >>>> >>>> ;(require future-visualizer) >>>> (define (euler141b) >>>> (define lim 1000000000000) >>>> (define ht (make-hash)) >>>> (for ([i (in-range 1 1000000)]) (hash-set! ht (sqr i) 1)) >>>> ; (visualize-futures >>>> (let ([f1 (future (λ () (find-progressive-num2 1 1000 4 lim ht)))] >>>> [f2 (future (λ () (find-progressive-num2 2 1000 4 lim ht)))] >>>> [f3 (future (λ () (find-progressive-num2 3 1000 4 lim ht)))]) >>>> (+ (find-progressive-num2 4 1000 4 lim ht) (touch f1) (touch f2) >>>> (touch f3)))) >>>> >>>> >>>> On Wed, Jul 24, 2013 at 9:46 PM, Robby Findler < >>>> ro...@eecs.northwestern.edu> wrote: >>>> >>>>> You might try places. Writing your own gcd seems straightforward. I'm >>>>> not sure about integer-sqrt?, tho. Maybe you could make a table or >>>>> something if you know there are not that many numbers. >>>>> >>>>> Or maybe someone will adjust the runtime to make those future safe! >>>>> >>>>> Robby >>>>> >>>>> >>>>> On Wed, Jul 24, 2013 at 11:34 PM, Joe Gilray <jgil...@gmail.com>wrote: >>>>> >>>>>> So I should write my own (gcd ) and (square? ) functions? >>>>>> >>>>>> I can try that, but isn't there a simple way to use threads? >>>>>> >>>>>> Thanks, >>>>>> -Joe >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> On Wed, Jul 24, 2013 at 7:47 PM, Robby Findler < >>>>>> ro...@eecs.northwestern.edu> wrote: >>>>>> >>>>>>> When I run this, the future visualizer shows that gcd and >>>>>>> square-number? block the futures. square-number? is implemented in TR >>>>>>> and >>>>>>> if you take it, you find that integer-sqrt also blocks the futures. I'm >>>>>>> not >>>>>>> sure if those functions can be made to run safely in futures or not. >>>>>>> >>>>>>> Robby >>>>>>> >>>>>>> >>>>>>> On Wed, Jul 24, 2013 at 7:26 PM, Joe Gilray <jgil...@gmail.com>wrote: >>>>>>> >>>>>>>> I have a ProjectEuler problem that I wanted to speed up so I >>>>>>>> thought I would try to speed it up with future / touch. >>>>>>>> >>>>>>>> I tried the following: >>>>>>>> >>>>>>>> ; function that searches for progressive numbers for a given range >>>>>>>> of b values >>>>>>>> (define (find-progressive-num b-start b-end b-incr lim) >>>>>>>> (for/sum ([b (in-range b-start b-end b-incr)]) >>>>>>>> (let loopa ([a (add1 b)] [suma 0]) >>>>>>>> (cond >>>>>>>> [(> (gcd a b) 1) (loopa (add1 a) suma)] >>>>>>>> [(>= (* a a a b) lim) suma] >>>>>>>> [else >>>>>>>> (let loopc ([c 1] [sumc 0]) >>>>>>>> (define n (+ (* a a a c c b) (* c b b))) >>>>>>>> (cond >>>>>>>> [(>= n lim) (loopa (add1 a) (+ suma sumc))] >>>>>>>> [(square-number? n) (loopc (add1 c) (+ sumc n))] >>>>>>>> [else (loopc (add1 c) sumc)]))])))) >>>>>>>> >>>>>>>> ; ProjectEuler problem #141 >>>>>>>> ; n = q * d + r >>>>>>>> ; q/d = d/r = a/b (where a and b are relatively prime) >>>>>>>> ; so d = a*r/b and q = a^2 * r / b^2 >>>>>>>> ; since a and b are coprime r must be divisible by b^2 or r = c*b^2 >>>>>>>> ; substituting: d = a*c*b and q = a^2*c >>>>>>>> ; n = a^3 * c^2 * b + c * b^2 >>>>>>>> (define (euler141) >>>>>>>> (define lim 10000000000) >>>>>>>> (let ([f1 (future (λ () (find-progressive-num 1 1000 2 lim)))]) >>>>>>>> (+ (find-progressive-num 2 1000 2 lim) (touch f1)))) >>>>>>>> >>>>>>>> Unfortunately this runs no faster than the sequential version. I >>>>>>>> tried using the future-visualizer but I couldn't understand what it was >>>>>>>> telling me (I guess some operation is blocking). I also tried finer >>>>>>>> grained threads (one for each value of b), but that did no better. >>>>>>>> >>>>>>>> Can anyone give me some pointers to successfully using future / >>>>>>>> touch? >>>>>>>> >>>>>>>> Thanks, >>>>>>>> -Joe >>>>>>>> >>>>>>>> ____________________ >>>>>>>> Racket Users list: >>>>>>>> http://lists.racket-lang.org/users >>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> >> >
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