SPINNING LOCKS
                spinlock_lock, spinlock_trylock, spinlock_unlock
                                 +------------+
                                 | spinlock_t |
                                 +------------+

                                   WAIT QUEUES
                         waitq_sleep_timeout, waitq_wakeup
                                   +---------+
                                   | waitq_t |
			           +---------+
				  /           \
               SEMAPHORES        /             \  CONDITION VARIABLES
 semaphore_down_timeout, semaphore_up    condvar_wait_timeout, condvar_signal
            +--------------+   /                 \   +-----------+
            | semaphore_t  |<-+                   +->| condvar_t |
            +--------------+                         +-----------+
                   |                                       ^
		   |                                       |
                   |                                +------+
                   V                               /           
                MUTEXES                           / READERS/WRITERS LOCKS
    mutex_lock_timeout, mutex_unlock   rwlock_reader/writer_lock_timeout, rwlock_unlock
              +---------+                       /        +----------+
	      | mutex_t |------------------------------->| rwlock_t |
	      +---------+                     /          +----------+
	           |                         /
		   +------------------------+