Priority Semaphores
Bernd Freisleben · The Computer Journal · 1989
Neither low-level mechanisms such as semaphores nor higher-level mechanisms such as path expressions provide a simple means of solving synchronisation problems involving the scheduling of processes or classes of processes according to different priorities. This paper presents a new set of primitives which are easy to use and simple to implement. Their use is described in terms of the familiar reader–writer problem and the general scheduling problem involving arbitrary levels of priority with support for pre-emption and shared access by certain process classes. An efficient implementation, which reduces to a minimum the number of calls required to the process scheduler, is then described.