Set the number of threads using openmp with .Fortran?

understanding is that this should also work on windows, is that correct?*
If so, what should I do? differently?

To get it to work on Linux, I modified my R script as follows:

#' OpenMP Hello World
#'
#' @param nthreads The number of threads that you want to use
#' @example
#' hello(nthreads=2)
#' @export
#' @useDynLib helloOpenMP, .registration = TRUE

hello <- function(nthreads=4) {
   (OpenMPController::omp_set_num_threads(nthreads))
  .Fortran("hello")
  return('Each thread will say hi to you!')
}

> hello(nthreads = 2) Hello from           0
 Hello from           1
[1] "Each thread will say hi to you!"




you!" without the Hello from X

Thanks for your help,

Ignacio





On Sat, Feb 2, 2019 at 11:34 AM Ignacio Martinez <ignacio82 at gmail.com>
wrote:

>
>
> I was able to make some progress by using this
> <https://github.com/bert9bert/ParallelForest/blob/master/src/Makevars> as
> a reference. Now:
>
> *This is my makevars:*
> #####  Compiler flags  #####
> PKG_FCFLAGS = $(SHLIB_OPENMP_FFLAGS)
> PKG_LIBS = $(SHLIB_OPENMP_CFLAGS)
>
> #####  Phony target for R's build system to invoke  #####
> all: $(SHLIB)
>
> #####  Clean target  #####
> clean:
> rm -f *.o *.mod
>
> And when I run my hello world function all the threads are used
> regardless of what i specify:
>
> > hello(ncores = 2) Hello from           1
>  Hello from           3
>  Hello from           0
>  Hello from           9
>  Hello from           8
>  Hello from           2
>  Hello from           6
>  Hello from          10
>  Hello from          11
>  Hello from           5
>  Hello from           7
>  Hello from           4
> $ncores
> [1] 2
>
>
>
> What am I missing? My Fortran subroutine uses !$call
> omp_set_num_threads(ncores) to set the number of threads. Why is this
> not working? How can I fix it?
>
> Thanks a lot for the help
>
> Ignacio
>
>
> On Fri, Feb 1, 2019 at 4:51 PM Ignacio Martinez <ignacio82 at gmail.com>
> wrote:
>
>> Hi everybody,
>>
>> I'm trying to develop an R package with Fortran and OpenMP. I wrote a
>> simple hello world but I'm not able to set the number of threads. I found this
>> old email chain
>> <http://r.789695.n4.nabble.com/Set-the-number-of-threads-using-openmp-with-C-td2284685.html> and
>> I tried to set my compile instructions accordingly but i had no luck.
>>
>> *This is my makevars:*
>>
>> PKG_FCFLAGS="-fno-stack-protector"
>> F90FLAGS =  "-fopenmp"
>> LDFLAGS = "-fopenmp"
>>
>> *This is my Fortran module:*
>>
>> module hello_openmp
>>    use omp_lib
>>    implicit none
>>    contains
>>
>> subroutine hello(ncores) bind(C, name="hello_")
>>   use, intrinsic                                         ::
>> iso_c_binding, only : c_double, c_int
>>   integer(c_int), intent(in)                             :: ncores
>>   integer                                                :: iam
>>   ! Specify number of threads to use:
>>   !$call omp_set_num_threads(ncores)
>>   !$omp parallel private(iam)
>>   iam=omp_get_thread_num()
>>   !$omp critical
>>   write(*,*) 'Hello from', iam
>>   !$omp end critical
>>   !$omp end parallel
>> end subroutine hello
>>
>> end module hello_openmp
>>
>>
>> *and this is my R function:*
>>
>> #'@export
>> #'@useDynLib helloOpenMP, .registration = TRUE
>>
>> hello <- function(ncores=4) {
>>   .Fortran("hello", ncores = as.integer(ncores))
>> }
>>
>>
>> *Alas, when I call hello things only run with one thread:*
>>
>> > hello(ncores = 2)$ncores
>>  Hello from           0
>> [1] 2
>>
>>
>> Could you point me in the right direction? What am I missing?
>>
>>
>> Thanks,
>>
>>
>> Ignacio
>>
>>

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