Locks rec_mutex. If rec_mutex is already locked by another
thread, the current thread will block until rec_mutex is
unlocked by the other thread. If rec_mutex is already locked
by the current thread, the 'lock count' of rec_mutex is increased.
The mutex will only become available again when it is unlocked
as many times as it has been locked.
Locks rec_mutex. If rec_mutex is already locked by another thread, the current thread will block until rec_mutex is unlocked by the other thread. If rec_mutex is already locked by the current thread, the 'lock count' of rec_mutex is increased. The mutex will only become available again when it is unlocked as many times as it has been locked.