pthread_mutex_unlock(3) on FreeBSD

The text 9b0c756942ce, as FreeBSD 3.2-RELEASE, FreeBSD 3.1-RELEASE, FreeBSD 3.0-RELEASE, FreeBSD 2.2.9-RELEASE, FreeBSD 2.2.8-RELEASE shipped it.

unlock a mutex

pthread_mutex_unlock(3) on FreeBSD now