Unlocks rec_mutex. If another thread is blocked in a
glib.rec_mutex.RecMutex.lock call for rec_mutex, it will become unblocked
and can lock rec_mutex itself.
Calling glib.rec_mutex.RecMutex.unlock on a recursive mutex that is not
locked by the current thread leads to undefined behaviour.
Unlocks rec_mutex. If another thread is blocked in a glib.rec_mutex.RecMutex.lock call for rec_mutex, it will become unblocked and can lock rec_mutex itself.
Calling glib.rec_mutex.RecMutex.unlock on a recursive mutex that is not locked by the current thread leads to undefined behaviour.