Parallel Programming in Fortran 95 using OpenMP - People

64 4. The OpenMP run-time library
In this example all the other threads, which do not own the lock, are not idle; instead,
they are performing another task. This is something not possible to achieve using OpenMP
directives. For certain problems, this possibility can be very useful, since the latency times
due to synchronizations are filled in with work.
In the previous two examples simple locks are used. Nestable locks are useful when a
subroutine needing them may be called from different locations inside a program. Then,
it is not necessary to worry about who is calling. For example:
module data_types
use omp_lib, only: OMP_nest_lock_kind
implicit none
type number
integer :: n
integer(OMP_nest_lock_kind) :: lck
end type number
end module data_types
!---------------------------------------------------------!
program Main
use omp_lib
use data_types
implicit none
type(number) :: x
x%n = 0
call OMP_init_lock(x%lck)
!$OMP PARALLEL SECTIONS SHARED(x)
!$OMP SECTION
call add(x,20)
!$OMP SECTION
call substract(x,10)
!$OMP END PARALLEL
call OMP_destroy_lock(lck)
end program Main
!---------------------------------------------------------!
subroutine add(x,d)
use omp_lib
use data_types
implicit none
type(number) :: x
integer :: d
call OMP_set_nest_lock(x%lck)
x%n = x%n + d
call OMP_unset_nest_lock(x%lck)
end subroutine add