Solaris™ Internals: Core Kernel Components

3.7. Turnstiles and Priority Inheritance

A turnstile is a data abstraction that encapsulates sleep queues and priority inheritance information associated with mutex locks and reader/writer locks. The mutex and RW lock code use a turnstile when a kernel thread needs to block on a requested lock. The sleep queues implemented for other resource waits do not provide an elegant method of dealing with the priority inversion problem through priority inheritance. Turnstiles were created to address that problem.

Priority inversion describes a scenario in which a higher-priority thread is unable to run because a lower-priority thread is holding a resource it needs, such as a lock. The Solaris kernel addresses the priority inversion problem in its turnstile ...