program main

c*********************************************************************72
c
cc MAIN is the main program for HELLO.
c
c  Discussion:
c
c    HELLO is a "Hello, World" program for OpenMP.
c
c    But we demonstrate a few simple features of OpenMP, including:
c
c    How you get the "include" file.
c    How you measure wall clock time.
c    How you find out how many processors are available.
c    How you find out which thread you are in a parallel section.
c    How you find out how many threads are available in a parallel section.
c    How you set the number of threads.
c
c  Licensing:
c
c    This code is distributed under the GNU LGPL license. 
c
c  Modified:
c
c    20 July 2008
c
c  Author:
c
c    John Burkardt
c
      include 'omp_lib.h'

      integer id
      integer proc_num
      integer thread_num
      double precision wtime
      double precision wtime1
      double precision wtime2

      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'HELLO'
      write ( *, '(a)' ) '  FORTRAN77/OpenMP version'

      wtime1 = omp_get_wtime ( )
c
c  How many processors are available?
c
      proc_num = omp_get_num_procs ( )

      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) '  The number of processors available:'
      write ( *, '(a,i8)' ) '  OMP_GET_NUM_PROCS () = ', proc_num
c
c  How many threads are available by default or environment setting?
c
c$omp parallel private ( id )

      id = omp_get_thread_num ( )
      thread_num = omp_get_num_threads ( )

      if ( id .eq. 0 ) then

        write ( *, '(a)' ) ' '
        write ( *, '(a)' ) '  Calling OMP_GET_NUM_THREADS inside a '
        write ( *, '(a)' ) '  parallel region, we get the number of'
        write ( *, '(a,i3)' ) '  threads is ', thread_num

      end if

      write ( *, '(a,i8,a,i8)' )
     &  '  This is process ', id, ' out of ', thread_num

c$omp end parallel
c
c  Request double the number of threads.
c
      thread_num = 2 * thread_num

      write ( *, '(a)' ) ' '
      write ( *, '(a,i8,a)' ) '  We request ', thread_num, ' threads.'

      call omp_set_num_threads ( thread_num )
c
c  Now how many threads do we see?
c
c$omp parallel private ( id )

      id = omp_get_thread_num ( )
      thread_num = omp_get_num_threads ( )

      if ( id .eq. 0 ) then

        write ( *, '(a)' ) ' '
        write ( *, '(a)' ) '  Calling OMP_GET_NUM_THREADS inside a '
        write ( *, '(a)' ) '  parallel region, we get the number of'
        write ( *, '(a,i3)' ) '  threads is ', thread_num

      end if

      write ( *, '(a,i8,a,i8)' )
     &  '  This is process ', id, ' out of ', thread_num

c$omp end parallel

c
c  Finish up by measuring the elapsed time.
c
      wtime2 = omp_get_wtime ( )
      wtime = wtime2 - wtime1

      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'HELLO'
      write ( *, '(a)' ) '  Normal end of execution.'

      write ( *, '(a)' ) ' '
      write ( *, '(a,g14.6)' ) '  Elapsed wall clock time = ', wtime

      stop
      end