[Rcpp-devel] RCppParallel Example Crashing R (Cross-Post from SO)

[Justace Clutter]

I would say that was it...  Thanks for catching that.  Sometimes the
smallest thing can get you.  I have updated the SO question with the answer.

Now that I got this working I am seeing great speed improvements:

b1 = R native code
b2 = Rcpp non parallel
b3 = Rcpp parallel

  test replications elapsed relative user.self sys.self user.child sys.child
1 b1()           10 1760.65   78.776   1753.76     0.56         NA        NA
2 b2()           10  128.78    5.762    128.38     0.05         NA        NA
3 b3()           10   22.35    1.000    170.68     0.06         NA        NA


On Sun, Nov 23, 2014 at 9:15 PM, Yixuan Qiu <yixuan.qiu at cos.name> wrote:

> Hello Justace,
> It seems that you should write down j < end rather than j <= end.
>
>
> Best,
> Yixuan
>
> 2014-11-23 21:10 GMT-05:00 Justace Clutter <justacec at gmail.com>:
>
>> I posted the following to SO earlier this morning and it was suggested
>> that I repost this question to the rcpp-devel list for exposure.  For
>> reference, the original posting is at
>> http://stackoverflow.com/questions/27089888/rcppparallel-example-crashing-r
>> .
>>
>> I have been trying to parallelize one of my Rcpp routines.  In doing so I
>> have been trying to follow the [Parallel Distance Calculation](
>> http://gallery.rcpp.org/articles/parallel-distance-matrix/) example from
>> jjalaire.  Unfortunately, once I got everything coded up and started to
>> play around, my R session would crash.  Sometimes after the first
>> execution, sometimes after the third.  To be honest, it was a crap shoot as
>> to when R would crash when I ran the routine.  So, I have paired down my
>> code to a small reproducible example to play with.
>>
>> ***Rcpp File (mytest.cpp)***
>>
>> ------------------------------------------------------------------------------------------------------------
>>     #include <Rcpp.h>
>>     // [[Rcpp::depends(RcppParallel)]]
>>     #include <RcppParallel.h>
>>
>>     using namespace std;
>>     using namespace Rcpp;
>>     using namespace RcppParallel;
>>
>>     struct MyThing : public Worker {
>>       RVector<double> _pc;
>>       RVector<double> _pcsd;
>>
>>       MyThing(Rcpp::NumericVector _pc, Rcpp::NumericVector _pcsd) :
>> _pc(_pc), _pcsd(_pcsd){}
>>
>>       void operator()(std::size_t begin, std::size_t end) {
>>
>>         for(int j = begin; j <= end; j++) {
>>           _pc[j] = 1;
>>     //      _pcsd[j] = 1;
>>         }
>>       }
>>     };
>>
>>     // [[Rcpp::export]]
>>     void calculateMyThingParallel() {
>>
>>       NumericVector _pc(100);
>>       NumericVector _pcsd(100);
>>
>>       MyThing mt(_pc, _pcsd);
>>
>>       parallelFor(0, 100, mt);
>>     }
>>
>> ------------------------------------------------------------------------------------------------------------
>>
>>
>> ***R Compilation and Execution Script (mytest.R)***
>>
>> ------------------------------------------------------------------------------------------------------------
>>     library(Rcpp)
>>     library(inline)
>>
>>     sourceCpp('mytest.cpp')
>>
>>     testmything = function() {
>>       calculateMyThingParallel()
>>     }
>>
>>     if(TRUE) {
>>       for(i in 1:20) {
>>         testmything()
>>       }
>>     }
>>
>> ------------------------------------------------------------------------------------------------------------
>>
>> The error seems to be directly related to my setting of the _pc and _pcsd
>> variables in the `operator()` method.  If I take those out things
>> dramatically improve.  Based on the Parallel Distance Calculation example,
>> I am not sure what it is that I have done wrong here.  I was under the
>> impression that RVector<type> was thread safe.  Although that is my
>> impression, I know this is an issue with threads somehow.  Can anybody help
>> me to understand why the above code randomly crashes my R sessions?
>>
>> For information I am running the following:
>>
>>   - Windows 7
>>   - R: 3.1.2
>>   - Rtools: 3.1
>>   - Rcpp: 0.11.3
>>   - inline: 0.3.13
>>   - RStudio: 0.99.62
>>
>>
>> _______________________________________________
>> Rcpp-devel mailing list
>> Rcpp-devel at lists.r-forge.r-project.org
>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>
>
>
>
> --
> Yixuan Qiu <yixuan.qiu at cos.name>
> Department of Statistics,
> Purdue University
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/rcpp-devel/attachments/20141123/2c05266e/attachment-0001.html>