omp_unset_lock– Unset simple lock
A simple lock about to be unset must have been locked by
omp_test_lock before. In addition, the lock must be held by the
omp_unset_lock. Then, the lock becomes unlocked. If one
or 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.