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