| lock_t | Basic lock, or spin-lock, used with LOCK() and related functions |
| mutex_t | Sleeping lock, used for mutual exclusion between upper-half instances. |
| sema_t | Semaphore object, used for general locking. |
| mrlock_t | Reader-writer locks, used with RW_RDLOCK() and related functions. |
| sv_t | Synchronization variable, used with SV_WAIT and related functions |
These lock types should be treated as opaque objects because their contents can change from release to release (and in fact their contents are different in IRIX 6.2 from previous releases).
The families of locking and synchronization functions contain functions for allocating, initializing, and freeing each type of lock. See "Waiting and Mutual Exclusion".