Parallel Programming in Fortran 95 using OpenMP - People

4.2. Lock routines 63
thread can perform the write process. Finally, since the lock is no longer needed after
the parallel region, it is eliminated with the aid of OMP destroy lock.
The previous example could also have been implemented using the OpenMP directive
!$OMP CRITICAL:
program Main
use omp_lib
implicit none
integer(kind = OMP_integer_kind) :: ID
!$OMP PARALLEL SHARED(LCK) PRIVATE(ID)
ID = OMP_get_thread_num()
!$OMP CRITICAL
write(*,*) "My thread is ", ID
!$OMP END CRITICAL
!$OMP END PARALLEL
end program Main
Looking at the previous example, the question rises about the necessity or use of the
run-time lock routines, if OpenMP directives are able of doing the same. Additionally to
the previously mentioned example with the matrix A, there are other cases where it is not
possible to emulate the effect of the lock routines using OpenMP directives. For example:
program Main
use omp_lib
implicit none
integer(kind = OMP_lock_kind) :: lck
integer(kind = OMP_integer_kind) :: ID
call OMP_init_lock(lck)
!$OMP PARALLEL SHARED(LCK) PRIVATE(ID)
ID = OMP_get_thread_num()
do while(.not.OMP_test_lock(lck))
... !work to do while the thread is waiting to get owner of the lock
enddo
... !work to do as the owner of the lock
!$OMP END PARALLEL
call OMP_destroy_lock(lck)
end program Main