Thanks for the replies. Regarding the answer by Dirk, I didn't feel like I still understood the reasoning why mclapply or foreach cannot handle XPtr objects. Instead of cluttering the SO question with comments I was getting the impression that this was a limitation inherited with R objects (which XPtr is supposed to be a proxy for an R object according to Dirk's comment). If this is not the case, I could repost this on Rcpp-devel unless it could be migrated.
Regards, Charles On Thu, May 12, 2016 at 8:11 AM, Mark van der Loo <mark.vander...@gmail.com> wrote: > Charles, > > 1. Perhaps this question is better directed at the R-help or > R-pacakge-devel mailinglist. > > 2. It basically means that R itself can only evaluate one R expression at > the time. > > The parallel package circumvents this by starting multiple R-sessions and > dividing workload. > > Compiled code called by R (such as C++ code through RCpp or C-code through > base R's interface) can execute multi-threaded code for internal purposes, > using e.g. openMP. A limitation is that compiled code cannot call R's C API > from multiple threads (in many cases). For example, it is not thread-safe > to create R-variables from multiple threads running in C. (R's variable > administration is such that the order of (un)making them from compiled code > matters). > > I am not very savvy on Rcpp or XPtr objects, but it appears that Dirk > provided answers about that in your SO-question. > > Best, > Mark > > > > > > > > > > > Op do 12 mei 2016 om 14:46 schreef Charles Determan <cdeterma...@gmail.com > >: > >> R Developers, >> >> Could someone help explain what it means that R is single threaded? I am >> trying to understand what is actually going on inside R when users want to >> parallelize code. For example, using mclapply or foreach (with some >> backend) somehow allows users to benefit from multiple CPUs. >> >> Similarly there is the RcppParallel package for RMatrix/RVector objects. >> But none of these address the general XPtr objects in Rcpp. Some readers >> here may recognize my question on SO ( >> >> http://stackoverflow.com/questions/37167479/rcpp-parallelize-functions-that-return-xptr >> ) >> where I was curious about parallel calls to C++/Rcpp functions that return >> XPtr objects. I am being a little more persistent here as this limitation >> provides a very hard stop on the development on one of my packages that >> heavily uses XPtr objects. It's not meant to be a criticism or intended >> to >> be rude, I just want to fully understand. >> >> I am willing to accept that it may be impossible currently but I want to >> at >> least understand why it is impossible so I can explain to future users why >> parallel functionality is not available. Which just echos my original >> question, what does it mean that R is single threaded? >> >> Kind Regards, >> Charles >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
