omp_unset_nest_lock– Unset nested lock
A nested lock about to be unset must have been locked by
omp_test_nested_lock before. In addition, the lock must be held by the
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.
OpenMP specification v4.5, Section 3.3.5.