R devel - Feb 2019 - Set the number of threads using openmp with .Fortran?

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

	[[alternative HTML version deleted]]

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
>
>
	[[alternative HTML version deleted]]

I got this to work on Linux but it is not working on Windows. *My
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!"



Alas, on Windows the same command just returns "Each thread will say hi to
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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