I have tried this with no luck. 2015-07-14 14:34 GMT+03:00 Romain Francois <rom...@r-enthusiasts.com>:
> Or just use a std::vector<double> for sg. That should do it. > > Romain > > Envoyé de mon iPhone > > > Le 14 juil. 2015 à 13:21, JJ Allaire <jj.alla...@gmail.com> a écrit : > > > > The examples in the RcppParallel documentation assume that access to > > vectors and matrixes are *aligned* (i.e. fall into neat buckets > > whereby reading and writing doesn't overlap between worker instances). > > Your example appears to access arbitrary elements of sg (depending on > > what's passed in gi) which probably creates overlapping reads/writes. > > You should also study the documentation for join carefully. > > > > There's nothing incorrect about RcppParallel's behavior here, rather > > you need to think more carefully about the access patterns of your > > data and how they might conflict. You may need to introduce locking to > > overcome the conflicts, which in turn could kill the performance > > benefit you gain from parallelism. No easy answers here :-\ > > > >> On Tue, Jul 14, 2015 at 7:15 AM, Danas Zuokas <danas.zuo...@gmail.com> > wrote: > >> Yes it is the same question on SO and I did consider RHertel's comments. > >> But this problem (sums by group id) is not parallelFor it is > parallelReduce: > >> I split vector, calculate sums and then aggregate those sums. > >> Please correct me if I am wrong. > >> > >> 2015-07-14 13:54 GMT+03:00 Dirk Eddelbuettel <e...@debian.org>: > >>> > >>> > >>> On 14 July 2015 at 09:25, Danas Zuokas wrote: > >>> | I have written parallel implementation of sums in groups using > >>> RcppParallel. > >>> > >>> Isn't this the same question as > >>> > >>> > http://stackoverflow.com/questions/31318419/when-calling-same-rcpp-function-several-times-different-results-are-returned > >>> > >>> You got some excellent comments there by SO user 'RHertel'. Did you > >>> consider those? > >>> > >>> Dirk > >>> > >>> | // [[Rcpp::depends(RcppParallel)]] > >>> | #include <Rcpp.h> > >>> | #include <RcppParallel.h> > >>> | using namespace Rcpp; > >>> | using namespace RcppParallel; > >>> | > >>> | struct SumsG: public Worker > >>> | { > >>> | const RVector<double> v; > >>> | const RVector<int> gi; > >>> | > >>> | RVector<double> sg; > >>> | > >>> | SumsG(const NumericVector v, const IntegerVector gi, NumericVector > >>> sg): v(v), gi(gi), sg(sg) {} > >>> | SumsG(const SumsG& p, Split): v(p.v), gi(p.gi), sg(p.sg) {} > >>> | > >>> | void operator()(std::size_t begin, std::size_t end) { > >>> | for (std::size_t i = begin; i < end; i++) { > >>> | sg[gi[i]] += v[i]; > >>> | } > >>> | } > >>> | > >>> | void join(const SumsG& p) { > >>> | for(std::size_t i = 0; i < sg.length(); i++) { > >>> | sg[i] += p.sg[i]; > >>> | } > >>> | } > >>> | }; > >>> | > >>> | // [[Rcpp::export]] > >>> | List sumsingroups(NumericVector v, IntegerVector gi, int ni) { > >>> | NumericVector sg(ni); > >>> | SumsG p(v, gi, sg); > >>> | parallelReduce(0, v.length(), p); > >>> | > >>> | return List::create(_["sg"] = p.sg); > >>> | } > >>> | > >>> | It compiles using Rcpp::sourceCpp. Now when I call it from R > >>> sumsingroups(1:10, > >>> | rep(0:1, each = 5), 2) several times I get the right answer (15 40) > and > >>> then > >>> | something different (usually some multiplicative of the right > answer). > >>> Running > >>> | > >>> | > >>> | res <- sumsingroups(1:10, rep(0:1, each = 5), 2) > >>> | for(i in 1:1000) { > >>> | tmp <- sumsingroups(1:10, rep(0:1, each = 5), 2) > >>> | if(res[[1]][1] != tmp[[1]][1]) break > >>> | Sys.sleep(0.1) > >>> | } > >>> | > >>> | breaks at random iteration returning > >>> | > >>> | $sg > >>> | [1] 60 160 > >>> | > >>> | or > >>> | > >>> | $sg > >>> | [1] 30 80 > >>> | > >>> | I am new to Rcpp and RcppParallel and do not know what could cause > such > >>> | behavior. > >>> | > >>> | Things that did not help: > >>> | > >>> | 1. Added for (std::size_t i = 0; i < sg.length(); i++) sg[i] = 0; to > >>> both of > >>> | constructors. > >>> | 2. Changed names so that they are different in Worker definition > and in > >>> | function implementation. > >>> | > >>> | _______________________________________________ > >>> | Rcpp-devel mailing list > >>> | Rcpp-devel@lists.r-forge.r-project.org > >>> | > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel > >>> > >>> -- > >>> http://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org > >> > >> > >> > >> _______________________________________________ > >> Rcpp-devel mailing list > >> Rcpp-devel@lists.r-forge.r-project.org > >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel > > _______________________________________________ > > Rcpp-devel mailing list > > Rcpp-devel@lists.r-forge.r-project.org > > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel >
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