Region System Calls
A region is a special type of a semaphore with only one unit. Regions are designed to be used by critical sections of code.
A thread that is “in control” of or waiting for a region cannot be suspended or deleted; so also, the process containing this thread cannot be deleted!
A thread that is in control of a region with a priority-based thread queue may have its thread priority dynamically adjusted by the INtime kernel to ensure that the thread releases the resource that is protected by the region.
Regions are released in the opposite order in which control was obtained.
The most recently obtained region is always released first.
An attempt to wait for a region that the thread already controls causes an error.