program openmp

!=========================================================================!
! OpenMP es un paradigma de programacion paralela de memoria compartida   !
! Se insertan secciones de codigo paralelo entre las directivas:          !
!    !$OMP PARALLEL                                                       !
!      .....                                                              !
!    !$OMP END PARALLEL                                                   !
! Se compila con la opcion: -fopenmp                                      !
!=========================================================================!

use omp_lib

integer :: nthreads, id
integer :: temp,suma
integer :: n=1000
integer,dimension(1000) :: vector,vector1

suma = 0

!$OMP PARALLEL PRIVATE(nthreads) 
id=omp_get_thread_num()      ! obtengo el thread id de turno
if (id == 0 ) then
   nthreads=omp_get_num_threads()   ! Para el thread root (0), obtengo la cantidad de threads
   print*, "Soy thread root (0). el nro de threads es: ",nthreads
end if
print*, "Hola mi thread id: ", id
!$OMP END PARALLEL



!============ ejemplo de parelizacion de un loop`========
!$OMP PARALLEL
!$OMP DO
do i = 1,n
   vector(i) = i
end do
!$OMP END DO
!$OMP END PARALLEL

print *,"vector: ",vector
print*,
print*,



!============ ciertas vars deben ser protegidas en el espacio de memoria del thread ============
!$OMP PARALLEL  PRIVATE(temp) SHARED(vector,vector1,n)
!$OMP DO
do i=1,n
   temp = vector(i)*2
   vector(i) = temp
   vector1(i) = vector(i)+3 
end do
!$OMP END DO
!$OMP END PARALLEL

print*,"vector: ",vector
print*,"-----------------------------------------"
print*,
print*,"vector1: ",vector1

!================== operaciones de reduccion ======================
! puede ser necesario tener variables que dependan del flujo del loop 
! la operacion de reduccion pemite reducir los valores de los distintos threads en uno unico
!$OMP PARALLEL
!$OMP DO REDUCTION(+:suma)
do i = 1,n
   suma = suma + vector(i)
end do

!$OMP END DO
!$OMP END PARALLEL
 print*, "suma: ",suma

end program openmp