ocked by
     'omp_set_nested_lock' or 'omp_test_nested_lock' before.  In
     addition, the lock must be held by the thread calling
     'omp_unset_nested_lock'.  If the nesting count drops to zero, the
     lock becomes unlocked.  If one ore more threads attempted to set
     the lock before, one of them is chosen to, again, set the lock to
     itself.

_C/C++_:
     _Prototype_:   'void omp_unset_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:   'subroutine omp_unset_nest_lock(nvar)'
                    'integer(omp_nest_lock_kind), intent(inout) :: nvar'

_See also_:
     *note omp_set_nest_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.5.